July 19, 2017 • 49 mins
In an effort to understand meteorology, we first must understand how weather works. What are the complex variables that determine weather patterns?
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Episode Transcript
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Speaker 1 (00:04):
Text with technology with tech Stuff from stuff works dot com.
Hey there, and welcome to tech Stuff. I'm your host,
Jonathan Strickland. I'm a senior writer here with how stuff
works dot com, and today I wanted to talk about
something I got to do. Those pretty cool just last week,
(00:26):
well last week as of the time I'm recording this,
I got to go visit the Weather Company to do
some interviews about meteorology and also ibm s Watson platform.
And it was a really cool experience to actually get
to walk around and see the various people who work
on weather science and try to figure out what was
(00:48):
the weather doing right now and was it going to
do next. I even managed to cause some problems for
the Weather Channel, but that wasn't entirely my fault. Uh
Now to explain us, the Weather Channel and the Weather
Company used to be the same entity, but then IBM
acquired the product and technology divisions of the Weather Company
(01:10):
and they bought those sections, but they didn't buy the
television broadcast business. So now they are two independent businesses.
One of them is run by IBM, the other one
is its own standalone weather broadcast service. That being said,
they still work very closely together. The Weather Channel still
gets a lot of its data and it's information from uh,
(01:32):
the Weather Company, so it's not like they are completely
independent of each other, and they both still exist in
the same building. They both are located out of the
same headquarters building here in Atlanta, Georgia. So there is
a Weather Channel studio that is in part of this building,
and there's the Weather Company offices that's on different floors
(01:55):
of the building, and UH they kind of co occupy
space even though they are no longer corporately speaking anyway
the same entity. So I thought it'd be fun to
do an episode about meteorology and weather models. This is
gonna be a two part episode because I have to
cover the science behind weather first and then talk about
(02:18):
meteorology to let you understand how meteorologists base their forecasts
off of weather conditions. You have to understand the complexities
of whether before you can really get a grip on
what it is that meteorologists do. And so in order
to do that, this episode is gonna be a little
less about tech and more about science in order for
(02:41):
us to have a deeper understanding of meteorology. In the
next episode, I should I should also mention We've covered
this topic in Tangential Ways and Older Tech Stuff episodes,
but it was more than overdue for a revisit. So
that's why we're going to talk about it today. We're
gonna really look at how weather systems actually work. Uh.
(03:07):
And before I get too far, I guess I should
actually explain what I meant when I said I caused
some problems for the Weather Channel. So while I was
at their headquarters, I was getting ready to shoot a
video interview with a man named Dale Eck, who is
the director of the Weather Forecast Center for the Weather Company.
(03:27):
So this guy is the head meteorologist in charge. He's
been doing work in meteorology for thirty years, and he
has a desk that's very close to the broadcast studio
for the Weather Channel. The broadcast studio has glass walls,
so you can see right through the walls. If you
ever watch a broadcast on the Weather Channel and they
(03:47):
shoot from inside the studio, you'll see people walking in
the background. You'll see desks and monitors and lots of
of colorful imagery because people have got a lot of
weather maps up in the background, so all of that's real.
Those are the actual people who work at the company. Uh,
and that's where we were shooting our videos. We were
(04:09):
shooting off to one side of this studio, and while
we're getting ready to shoot, we had set up the camera.
I was miked. We had a shotgun mike so that
we can pick up Mr X his his contributions. We
were off to one side of the studio, so we're
up against where the glass walls are, but we weren't
(04:32):
directly across from where the cameras were set up. Um,
they did have sets where they could pivot around where
we would have essentially been in the background for those
those shots if they had set something up, but they
were mostly shooting directly against the back wall of the
studio and we were on one of the sidewalls. So
we're getting ready to shoot, and one of the the
(04:55):
employees over at the Weather Company very helpfully pointed out
a bank of light switches that were in control of
production lights. So flipping those switches would turn several lights
on in the area we were standing in That would
end up providing a lot more light for our video,
and that is really important if you're shooting video, you
(05:17):
need good lighting. So after being told about them, we
turned them on. We being my producer, turned them on,
and you know, he was essentially told to do it,
so that's what he did. And it didn't take very
long before a floor manager for the Weather Channel, very
calmly walked up and asked us to knock that off.
(05:38):
Although I should say she was incredibly friendly and professional.
She wasn't mean about it at all, but explained that
the light that we had created was bleeding into the set.
You know, it's a glass wall, lights just passing right
through it, so it was affecting the shot for the
actual Weather Channel, you know, the nationally televised Weather Channel broadcast.
(06:03):
So my little YouTube video that I was shooting was
impacting a nationally broadcast television scene. So that was a
little bit of a Oopsie Daisy moment for me and
my team. The nice thing is it was probably pretty
subtle and it probably didn't have that big of an
(06:24):
impact at all, but still it made us feel like
we were kind of jerk faces. And if you were
watching the Weather Channel last week or this would that
would have been, um, you know, this is June right now,
so it would have been June Thursday. If you were
watching the Weather Channel, you know, trying to keep up
(06:47):
to date with Tropical Storm Cindy, and you were wondering,
why is the lighting going all crazy in this broadcast?
That was us are bad, But I have to really
thank everyone who works for the Weather Channel and the
Weather Company. They were very generous with their time and
(07:08):
they gave us lots of leeway to shoot really cool video.
So it was a great visit and it helped me
appreciate the complexities of meteorology on a deeper level. So
let's now talk about weather forecasting. It's an interesting business.
At a very very high level, like a super simplistic level.
(07:31):
Weather forecasting, at least in the recent past, involved taking
lots of observations, comparing those observations of present conditions to
things that had happened before in the past, researching what
followed those similar conditions when they did happen before, and
then making a guess as to what is going to
(07:51):
happen next based upon past experience. That's a drastic oversimplification,
and really it's saying that it's about pattern recognition, and like,
let's say, if you notice that when the temperature goes
up at a certain time of day, with these other
factors in place, the chance of rain increases drastically based
upon past experience. You might use that to help forecast
(08:15):
the weather and say there's a good chance that's going
to rain later today because these other factors are at play,
and other times when that has happened, it's rained. But
let me give you a more simple example about how
this might work out. Let's say you've got some basic
meteorological gear, like some sensors, a barometer, wind speed, indicator,
(08:39):
wind direction. You know how much humidity is in the air.
You know the temperature because you've got a thermometer, all
these sort of things. These are the typical sensors you
would find at a weather observation point. You've kept a
log book of weather for this particular location that goes
back two decades, so you've got twenty years of information
(09:01):
at your disposal, twenty years of collections of data points
and what was actually happening with the weather. You make
your observation in the morning, you note the temperature, the
air pressure, You've got all these different factors, and then
you look at your log books and you look for
days that are similar to the conditions you are currently observing.
(09:27):
Then you look to see what happened later on those
previous days. So if you had one hundred mornings that
are similar to the conditions of the morning you are
concerned with, like this morning, you wake up, this morning,
you take readings, you find one other, one other examples
in your log book that are similar to today, and
(09:47):
then you notice that on seventy of those one days
it rained. You could say there's a seventy chance of rain.
That seventy of the time, when conditions were the way
they are right now, it rained. Of those days where
the conditions were exactly the way they are right now,
it did not rain. And I don't really mean exactly.
(10:10):
I guess I should say approximately, because weather is incredibly
complicated and to have two weather systems behave exactly the
same way under the same circumstances is pretty unlikely. But this,
again is a drastic oversimplification of how weather forecasts work.
(10:30):
It does give you a basic idea of the the
principle behind meteorological forecasts, at least until more recently we
get into weather simulation and huge amounts of data processing.
Today that gets a lot more sophisticated than just what
are the conditions today and what happened on previous occasions
(10:52):
when those conditions were present. But keep in mind meteorology
is constantly evolving. It has ever reached a perfect level status,
as anyone who has depended upon a weather forecast knows,
you've probably in the past looked at a weather forecast
and said, oh, there's no chance of rain, and then
a thunderstorm pops up. Well, that's because weather is really
(11:15):
complicated and sometimes a hyper local event can occur that
is impossible to really predict when you're looking at, say
a regional weather forecast, because your fidelity doesn't get that small.
You can't predict everything that happens within that region with
perfect accuracy. You're giving more of an overall look for
(11:37):
the region as a whole. So it gets really complex.
There are a lot of different variables, and there's a
lot of different technology that goes into gathering the information
about those variables and then crunching those numbers to make
some meaning out of it, which is why it's an
ideal topic or text stuff. Now, if we are to
(12:00):
understand really how meteorology works, we've we've got to take
a deep looking at a look at whether or not
a deep looking that makes no sense, but a deep
look at whether. We at least need to get as
deep in understanding for whether as we can in a
casual podcast setting. So the first step is acknowledging the
difference between weather and climate. This is important because I
(12:23):
see these two concepts conflated all the time, and frequently
it pops up in in political discussions because you have
people with agendas who want to push specific action items
that favor their philosophy over the action items of people
who oppose their philosophy. And frequently in those discussions, people
(12:47):
will start to make generalizations about weather and climate that are,
if not untrue, at least inaccurate. So let's settle that.
And I know all of you know this, but it's
good to at least start with the baseline. So whether
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refers to the current state of the atmosphere, it's it's timely.
It's either something that's happening right now, like you're talking
about the weather right now, you're talking about a weather forecast.
You're talking about something that's going to happen within the
next day to ten days maybe or maybe a little
further out, but that's about it. Or you're talking about
what has happened over the past few days, but that's
(13:29):
about it. Like it's about a month or so of
time stretching backward and forward uh in total from where
you are right now, So it's very timely. Climate, however,
is about whether patterns over vast spans of time or
at least several years, if not decades of time. So
(13:50):
climate is more about general weather patterns and how they
behave over these these uh the span of years. So
climate change is very gradual. That means that you're not
likely to notice climate change on a day to day basis,
which means that if you use an argument like global
(14:13):
warming isn't real because it's snowed last winter, that's a
fallacious argument because you're talking there about whether not climate
climate would be a gradual change, which over the course
of several years might mean that after several years it's
snowing less and less, or the snow is not lasting
(14:33):
very long, the the period of time where it does
snow is decreasing, like it's becoming more concentrated in a
narrower span of days. Those are the sort of things
we might see as a result of climate change over
the course of several years. But we humans aren't very
good at conceptualizing that. We tend to focus on stuff
(14:55):
that we've recently observed, but particularly when it's something that's
happening at at times. So if you were to have
an unusually mild summer, you might think, well, that says
that climate change is is bogus because I should it
should be much hotter than that. That's not taking into
(15:15):
account the long term changes in trends. So again, climate
is the long view, whether is what is happening right now?
Now that we've established that, we can get past those
weird straw man arguments people make that tried to discredit
(15:36):
one another for whatever philosophy they have using weather in
place of climate, it just doesn't work. Climate change, by
the way, is a real thing. Uh, it is a
scientific consensus has found that climate change is real and
that humans have had an impact, a significant impact on
climate change. And consensus is no small matter getting scientists
(15:59):
to agree to some thing. That's I mean, science is
all about questioning claims and putting them to the test.
That's how science works is you make an observation or
you make a prediction, and then you test it over
and over and over again to see if it holds true.
If you get to a scientific consensus where a lot
of scientists, the vast majority of them all agree on something,
(16:20):
that's a powerful statement, although we often will see that dismissed.
Uh So, again, this isn't to get political. This is
just stating a scientific fact, not a political effect. Climate
change is real, humans have an impact on it. What
does that mean politically, Well, that's a totally different discussion.
(16:41):
So there's probably people out there who wish that climate
change wasn't a real thing, that this was all just
a manufactured story. But if wishes were horses, beggars would ride.
As my old social studies teacher would say, So, climate
describes weather trends over many, many years, and weather describes
changing atmospheric conditions on a much shorter time span. And
(17:03):
our atmosphere is where weather happens. Again, not a big shock.
This is elementary school science. It's made up of a
lot of gases our atmosphere. The big one, of course,
is nitrogen, that makes up about of the atmosphere. Then
comes oxygen, which is my personal favorite. I'm totally breathless
(17:23):
without oxygen. It makes up about of the art's atmosphere,
and then you've got less than a percent of argone
point zero three carbon dioxide, and the rest of it
is made up of small amounts of water, vapor, hydrogen, ozone, neon, helium, crypton,
and xenon. Our atmosphere is pretty thick, and there's not
(17:47):
really a hard barrier between the top of the atmosphere
in the beginning of space. It's kind of a fuzzy barrier,
and there's not like you can't point to a specific
height above the Earth and say, specifically, at this point
the atmosphere ends, and this is just empty space beyond it.
The best you can do is do an estimation. So
(18:09):
generally speaking, the atmosphere pretty much peters out into nothing
once you reach about six hundred miles or one thousand
kilometers above sea level, So you gotta go at sea
level six d miles up and you're pretty much at
the point where you're not going to find any molecules
of any significant number that represent an atmosphere. Gravity holds
(18:33):
the gases down to the planet, which I'm sure seems
pretty obvious. Without gravity, the atmosphere would dissipate into space,
but don't worry, so would we. So the gases wouldn't
be lonely for very long. It's a moot point because
we do have gravity, so we're good. The atmosphere is
also a very heavy thing. Collectively, if you take all
(18:55):
of the other's atmosphere, it weighs five point five quadrillion uns.
That's four point nine nine quadrillion metric tons. Again, that's collective.
That's all the atmosphere that surrounds our planet. Obviously, you
are not walking around with a few quadrillion tons of
weight on top of you. This weight of the atmosphere
(19:17):
creates atmospheric pressure. The pressure is different at various altitudes,
which makes sense. If you are on top of a mountain,
you actually have less atmosphere above you, like there's less
air between you and outer space. If you're on top
of a mountain, then if you were standing in the
middle of a valley, there would be more air between
(19:38):
you and outer space. Because again remember we're measuring that
by sea level, so your altitude makes a big difference.
You would have a lower atmospheric pressure at a high
altitude than you would somewhere with a low altitude. The
pressure also compresses the gases in the atmosphere, so air
closer to the surface of the planet is more dense
(20:00):
than air that's near the edges of space, and all
the weight above that low altitude air is forcing the
various molecules to get all chummy with each other. So
you've got denser air closer to the surface. So I've
got more to say about atmospheric pressure and it's rolling
weather in just a minute. But before I jump into that,
(20:21):
let me take a breath and thank our sponsor. All right,
So let's say you are at sea level. The average
atmospheric pressure at sea level is fourteen point seven pounds
or six point seven kilograms per square inch. As you
(20:42):
climb in altitude, the pressure and density of the air
around you decreases until you reach a point where it
would be quite difficult to breathe, and you need to
breathe in more in order to get enough oxygen so
that you can continue, you know, living. So you might
take a lungfull and not get enough oxygen to remain
(21:03):
conscious if you're at a high enough altitude, which is
part of the reason why mountain climbers have to tackle
really tall mountains and stages. They have to have camps
where they take a break and acclimate to the lower
air pressure and lower air density of higher altitudes. So
gravity obviously plays a big part in weather systems keeping
(21:24):
our atmosphere nice and in place. The Sun obviously also
contributes to our weather patterns. The Sun is the direct
source for most of the energy here on Earth. Some
of the energy of the Sun gives off warms our
atmosphere directly, but most atmospheric warming actually comes not from
sunlight coming down to Earth, but rather the heat that
(21:45):
is radiated off of Earth. The heat that the Earth
has absorbed from the Sun. So the plant itself absorbs
heat and then releases that heat later on. That tends
to be what heats up most of the atmosphere. The
reason this happens is because the type of radiation that
we're talking about radiation from the Sun is short wave
(22:06):
radiation that easily passes through the gases the atmosphere and
then it gets absorbed by the planet. When the planet
emits heat, it's emitting long wave radiation. Long wave radiation
gets absorbed readily by the atmosphere, so the atmosphere warms
from the ground up. And that also explains why if
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you were to climb a mountain as you would climb
in elevation, the temperature would decrease to a point anyway
in the troposphere. So there are four layers of Earth's atmosphere,
and you classify those four layers by temperature ranges. The
layers aren't uniform. Their thickness varies a bit as you
(22:50):
go from region to region around the Earth, but they're
roughly outer shells of Earth. The innermost one is the atmosphere,
as the level closest to the surface of the Earth.
It ends somewhere around seven miles or eleven kilometers above
sea level on average. Throughout the troposphere, as you climb altitudes,
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the temperature drops. That's one of the markers for the
troposphere that all stops when you pass the tropo pause.
That is the boundary between the troposphere and the stratosphere.
That is the next layer out from the troposphere. The
tropospheres where all of Earth's weather happens. It also accounts
for eighty percent of the air in our atmosphere. The
(23:35):
other three layers contain the remaining twenty of the air
in our atmosphere. Now, remember our atmosphere extends all the
way up to six hundred miles above sea level, whereas
the troposphere ends at seven miles above sea level. So
within those first seven miles out of six hundred, you
(23:56):
have eighty percent of the air in our atmosphere. That
tells you how densely packed those gases are. The stratosphere
extends from the tropopause up to about thirty miles above
sea level or forty eight kilometers. For the first few miles,
the temperature of the stratosphere remains pretty stable with regards
to the tropopause below. So remember you climb up through
(24:18):
the troposphere, the temperature starts to go down. When you
hit the tropopause, the temperature pretty much stabilizes, and then
you're in the stratosphere and the temperature remains stable for
the first several miles, but then the temperatures actually start
to increase. It starts to get warmer as you move
through the stratosphere. This is because at those upper levels
(24:39):
of the stratosphere you can find ozone. Ozone can absorb
ultra violet radiation from the Sun. Unlike most of the
other gases, it actually can absorb some of those short
wave radiations. So the ozone heats up, which means the
upper levels of the stratosphere are also warmer than the
lower levels. Above the amosphere is the miso sphere, where
(25:02):
temperatures decline again, getting to be the coldest temperatures in
Earth's atmosphere. Those temperatures hovered around minus degrees fahrenheit or
minus nineties celsius. And the final layer of the atmosphere
is the thermosphere, which shares its outer body with space,
and the air here is not dense at all. It's
(25:24):
actually pretty widely spread out. The molecules are very thin like,
it's very thinly populated, the opposite of very dense. In
other words, the interesting thing here is that the thermosphere
technically gets really freaking hot. We're talking like degrees fahrenheit
(25:44):
or shundred degrees celsius. But because those molecules are so
few and far between, it would not feel hot to
you because you wouldn't be in contact with these highly
energized molecules. They're spread too far apart from each other.
It's kind of like being inside and an enormous arena
stadium and there are a dozen ping pong balls flying around.
(26:05):
The Odds of any of those ping pong balls actually
making contact with you are pretty low. Because you're in
a big area with these tiny things moving around, it's
just not likely that you're gonna encounter one of them.
Same thing is kind of true with molecules out in
uh the the thermosphere. So while those molecules will be
quite warm and you're not likely to run into them.
(26:28):
Now back here on the surface, where we have the
troposphere to deal with, you've got atmospheric pressure, you've got temperature.
These two factors affect atmospheric movement. As gases heat up,
the molecules in those gases move around more, they spread out,
they become less dense. When the density changes enough so
that the air above is more dense than the air below,
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that denser air is going to sink down and displace
the warm air that is there. You might have heard
the phrase warm air rises, Well, it's true, but it's
really probably more accurate to say cold air sinks. If
you were to have a very dense fluid and you
put it on top of a less dense fluid, you'd
(27:12):
see the dense fluids sink down to the bottom and
the less dense fluid would rise to the top. Same
thing is true with atmospheres and our atmosphere is a fluid,
so these denser, colder areas sink down and that pushes
the warm air up to the top. So this way
you get some fluid movement in our atmosphere as different
(27:34):
areas start to warm up or cool down. Now, as
that warm air does rise, it actually starts to cool
down because it's going up in altitude. And remember and
those altitudes in the troposphere. The higher you go, the
cooler it gets. So the warm air initially gets pushed
up by colder air, but then the warm hair itself
begins to cool and it has a tendency to sink again. Now,
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if everything we're equal, if our planet did not rotate,
if we didn't have any uh variation in parts of
the plant that warmed or cooled, if it all warmed
or cooled at the same time, our atmosphere behavior would
be really simple. It would expand when sun was hitting it,
(28:17):
and it would contract when the sun wasn't hitting it.
So you would just see the atmosphere kind of breathe
that would move out and in based upon the warming
and cooling, and that's all it would do. You wouldn't
get a whole lot of other movement there, but that's
not our reality. The reality is we have a lot
of other factors at play that create the the conditions
(28:39):
that allow wind to generate. So regions of the Earth
warm at different rates at different speeds, and thus regions
of our atmosphere end up warming at those different speeds,
and that regional variation causes a lot of churning in
the atmosphere, which creates pressure differentials between regions, thus leading
(29:00):
to wind. So let's take a city and countryside example
to kind of understand what I mean by this. If
you have a city, the city heats up faster than
the countryside would during the day due to a lot
of the materials in the city, you know, concrete, blacktop,
these sort of materials soak up a lot of heat,
so they're going to get much warmer than the countryside wood,
(29:21):
which doesn't have those sort of materials all through it.
So you've probably heard of the island effect, which is
where you get an island of heat because you've got
a bunch of of mass that just absorbs heat readily
in one space, and it creates an island effect within
the region. That's what we're talking about here. The city
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ends up soaking up a lot of heat and then
releases that heat. Over the course of many hours. As
cities radiate heat, that heat warms the atmosphere that's surrounding
the city's That warm air is less dense than the
cold air that's further on the outskirts of the city,
out in the countryside, So the warm air is an
area of low pressure because it's less dense. It's actually
(30:04):
exerting less pressure on the city because it weighs less.
It is less dense than the cold air that's around it,
or the relatively cold air compared to the city's air.
So the cold air blows into the city because it
wants to move from an area of high pressure to
an area of low pressure, sort of that. In tropic movement,
the warm air is forced upwards in an updraft and
(30:29):
starts to climb up into the upper levels of the troposphere.
As it does so, it starts to cool, and once
it cools enough, it needs to come back down. But
because cities soak up so much heat, and because the
updraft can be so powerful, the cold air can't just
sink back down to where it was. It actually has
to move outward and then sink down further out from
(30:51):
where the city is. It's almost like a fountain. You
would see the water of the fountain come up in
a column and then spread out in a fan the
top and come back down to the base of the fountain.
That's sort of what's happening, except with atmosphere, not with water,
although it could be with water. We'll get into rain
in just a second. So at night the city would
(31:13):
cool faster than the countryside does, and then the trend
would reverse itself. We would have winds that are originating
essentially from the city moving out to the countryside. This
little system is what we would call a convection cell,
and convection is when the movement of mass or circulation
of atmosphere transfers heat through some sort of substance. In
(31:34):
this case, we're talking about the planet and the atmosphere.
On a larger scale, forces affect these movements to generate
massive weather weather patterns. The poles are areas of high
pressure and the equator is an area of low pressure.
You've got a lot warmer air moist air in the equator,
a lot cold or dry air over at the poles.
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And if that was all there were to it, we
would see winds coming from the north and south and
converging towards the equator. But there are a lot of
other areas of high and low pressure across the surface
of the Earth. It's not just the polls and the equator.
There's a lot of variation there due to tons of
different stuff, including topography like mountains and valleys, that sort
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of thing, deserts. So you have lots of areas of
high and low pressure across the surface of the Earth,
which creates natural pressure gradients, and that generates wind. Wind
from high pressure areas cycle inward to low pressure areas.
In fact, we call a low pressure center a cyclone.
Now it's not the same thing as cyclones that are
(32:36):
also known as hurricanes, slightly different, although there is a
circular motion to it. That's where you get that cyclone
name there. High pressure centers are anti cyclones, as an
anti not as an anti cyclone the sister of my father,
who we don't talk about. It's a different thing entirely.
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High pressure air moves in a down undraft as low
pressure air moves in an updraft, and Earth's rotation also
gets into the game. This is where we get the
Coriolis effect. In the northern hemisphere, wind deflects towards the right.
In the southern hemisphere it's deflected to the left. The
Coriolis effect really influences large fluid masses, by the way,
(33:18):
so it does not necessarily affect which way the water
goes down a sink or a toilet, despite what the
Simpsons would have you believe. Uh, there are a lot
of other smaller things that can affect the way water
drains down the drain and is not the Coriolis effect.
Coriolis effect is really for very big systems, not for
small systems like a a sink full of water or
(33:42):
a tub full of water. But the Coriolis effect does
break the two big convection cells that otherwise would exist,
you know, the ones that would be the North and
South hemispheres, and it ends up creating three different types
of convection cells. You get two of each type. You
have two polar cells to Hadley cells, and two Feral cells.
(34:05):
And the Hadley and Feral cells are named after meteorologists
who discovered them. This is the important thing, really is
to remember that these convection cells have a really big
impact on on larger weather trends, global weather trends now
where the wind blows down here near the surface, air
encounters resistance in the form of friction, but a bit
(34:27):
higher up in the atmosphere that's not a problem. So
jet streams shoot around at fairly high altitudes we're talking
twenty thoty five thou feet or between six and fourteen kilometers,
and they don't encounter this friction. They move it incredible speeds.
They can carry temperature changes effectively around the world. So
you'll see things about jet stream and how that will
(34:48):
affect local weather patterns depending upon where you live. High
altitude winds, the coreolas, affected pressure gradients are the three
big influencers of wind generation on a global scale. But
remember regional geography, coastlines, mountains, valleys, all of that also
has an effect. Regional heating and cooling has an effect.
(35:09):
So these big factors are the major variables, but they're
not the only ones. And now you're starting to see
all the complications that come into just describing weather, let
alone predicting it. But that covers wind. Rain is pretty
easy to explain. The water cycle on Earth is pretty
(35:31):
much a closed system. Water evaporates into the atmosphere. Water
vapor condenses as it cools down, so it condenses from
water vapor and turns into liquid water. It starts to
cling to specs of stuff in the atmosphere, little particles
of dust. Uh. That ends up becoming the nucleic sites
for rain drops. If it is able to accumulate enough
(35:51):
water vapor. The cooling happens. Once water vapor rises high
enough into the air, and with enough cooling water vapor,
you get clouds. Wind will push and reshape the clouds,
moving them to different locations. And if you get enough
water vapor condensing around those nucleic sites, it becomes too
heavy to remain aloft by the winds alone, and it
(36:13):
starts to fall. And that's when you get rain, or
if it's really cold, you might get sleet or freezing
rain or snow. But you get what I mean, you
get precipitation. I've got a little bit more to say
about the water cycle and other elements of weather, but
before I jump into that, let's take another quick break
and thank our sponsor. So water vapor can be pushed
(36:44):
into higher altitudes through several different ways. One of those
is just changes in elevation in the land. So if
you have a warm air system and it's got a
lot of water vapor in it, and it moves across
flat lands and start to encounter mountains, it has to
conform with the topography, so as it gets pushed against
(37:08):
the mountain, it actually starts to go up the mountain,
and that means some of that water vapor gets pushed
up to higher elevations and it gets high enough, then
it can cool down, condense, turn into clouds, and eventually
even turn into precipitation. So if you've ever heard about
windward and leeward that's what this refers to. The windward
(37:28):
side of a mountain is the side that faces the
area where wind comes in from. So traditionally the direction
front which fronts move through, so you have a warm
air mass coming through to a hit a mountain, that's
the windward side. The leeward side tends to be gloomy
and covered in rain a lot because that water vapor
(37:49):
that hits the windward side gets forced upwards into the
higher parts of the atmosphere or of the troposphere i
should say, condenses into uh into clouds, and then eventually
can turn into rain or precipitation of other forms, and
on the leeward side that's where you get that rain,
and you also have a lot of cloud cover. So
there's a sunny side of a mountain and there's the
(38:11):
less sunny side of the mountain. Typically, and uh, that's
one way water vapora can be pushed into high altitudes
to form clouds. But there's also an way called frontal wedging,
which originally I thought was something that happened to me
back in middle school, but it turns out I was
thinking of something totally different. This is actually when warm
air ends up colliding with a cold air mass, and
(38:35):
the cold air mass sort sort of acts like a
ramp because remember a cold air is more dense than
warm air, so warm air is going to float above
or rise over cold air. It ends up being wedged
on top of cold air. That pushes warm water vapor
up into those higher altitudes again where it can condense
(38:55):
and form clouds. So if you have a warm air
mass moving into to a cold front, or rather a
cold air mass, not a cold front, then this can happen.
The warm air will rise over the cold air, the
water vapor in the warm air will slowly condense and
then you end up getting clouds as a result. This
is typically what we call a front. So a warm
(39:17):
front is when warm air moves into an area that
has cold air in it. A cold front is when
cold air moves into an area that has warm air
into it. So essentially it's a low pressure system moving
into a high pressure system, or a high pressure system
moving into a low pressure system. And then you've got
these masses colliding with one another. Really, it just depends
(39:37):
on what type of air mass is moving in and
what type of air mass is currently in the region.
That determines whether it's a cold front or a warm front.
But then you also have two other types of fronts.
You have a stationary front, and these cases you have
two air masses that are unable to advance against each other.
They kind of just bump up against each other and
(39:59):
stay there. And then you have the occluded front. This
is when a cold front moves fast enough to overtake
a moving warm front. So that's another way that water
vapor can be pushed up into the higher elevations. Way
number three for water vapor to go moved moving up
to those higher altitudes is called convergence. Now this is
(40:19):
not the same type of convergence I typically like to
talk about here on tech stuff. It's when two similar
air masses collide and both end up forcing air into
an updraft, which includes water vapor. And so yet again
we see water vapor get pushed up and cooling down
to condense. But that's convergence. And finally you have what
(40:40):
is called convective lifting. This is a localized effect, so
it's not something that happens on regional or global scales,
but rather very local scales. It's when Earth's radiation of
heat causes a pocket of air to warm and rise,
forcing water vapor up in the process and creating clouds.
This requires having an area that is absorbing a lot
(41:01):
more heat than its surroundings typically do. So a good
example might be a large airport. The airport's got a
lot of surface area that gets exposure to the sun.
It absorbs a lot of heat, much more heat than
the surrounding area typically does, and so it releases more
heat and as a result, you can get cloud formation
above airports just because of this localized convective lifting. So
(41:24):
now we understand the general principles behind weather that air
pressure temperature and the presence of water vapor matter a lot.
Now other things matter too, of course. The Earth's access,
for example, is that twenty three and a half degrees tilt,
which means we're likely, uh, we're we're we're like, we're bobbling,
bobbling around like a wobbly top as we orbit the Sun,
(41:45):
and this causes different parts of the planet to receive
more or less sun exposure during certain parts of the year.
That ends up affecting weather patterns and seasonal patterns and weather.
It's complicated in that incoming systems can have a dramatic
effect on systems that are already within a region. So
it's an enormous, chaotic mess with lots of variables, and
(42:05):
that's part of the reason why meteorology is so darned challenging.
We cannot isolate those variables. We cannot really understand how
to properly weight all of them in every situation. That is,
determining which variables are most important under any given set
of circumstances, it's really really hard to do. So you
(42:26):
might say that under a certain set of conditions, the
temperature of the air is the most important variable, and
that depending upon that temperature of the air, certain outcomes
are almost absolutely gonna happen, right But then you might say,
under slightly different circumstances, temperature no longer becomes the most
important variable. Now it's air pressure that's more important than temperature.
(42:50):
Weather is so complicated, and there's so many different variables
that have different weights and different situations that it becomes very,
very difficult to understand what is happening right now, let
alone predicting what is going to happen. In fact, I
find it amazing that we can manage to have any
real accuracy and weather predictions at all, because it's so
(43:10):
crazy complicated. Now, Before I wrap up, I thought it'd
be fun to talk about some of the earlier forms
of weather forecasting before you know, sensors and and observing
stations and computer models came along. The stuff we used
to do before we had all those sophisticated technologies and
really a truly astonishing amount of processing power capable of
(43:34):
handling all those points of data simultaneously. Because we humans
have been trying to suss out weather for centuries, knowing
what the weather will be like has a tremendous impact
on our decisions like should I buy tickets to that
outdoor sporting event, or how can I plot a course
for these shipping goods to get from point A to
point B with the least amount of delay and fuel consumption.
(43:55):
But our methods for making predictions haven't always been terribly scientific,
and it's heart a lot of our weather predictions were
centered on pattern recognition. That's what I alluded to at
the top of this episode. We would say, hey, remember
that other day that was a lot like today. Well,
it rained like a son of a gun later on
the evening, and that other day, I bet that happens
(44:16):
again tonight. I bet we get more rain tonight, because
that's what happened that other day. Early human civilizations made
similar observations and predictions, which range from the immediate, which
would involve something like I better seek shelter because it
looks like it's going to storm, to more long term planning,
such as I've noticed that the weather seems to get
warmer for a while, and then everything is growing, and
(44:38):
then after a while the weather starts getting cold and
everything stops growing. So maybe I should grow stuff in
this one part of time and harvest stuff at this
other part of time. In other words, we started learning
more about how seasons work. There are some changes in
conditions that are a bit too subtle for humans to
pick up on them by themselves, but they're are other
(45:00):
animals that are more sensitive to those changes, things like
atmospheric pressure, for example, and so humans would sometimes observe
changes in animal behavior that would precede certain types of
weather events. Those behaviors would become associated with weather, leading
to some folk knowledge about what it means when your cow,
I don't know, switches from Xbox to PlayStation. I guess
(45:23):
I should point out right now that I haven't been
on a farm in like thirty years, so my understanding
of animal behavior might be a little off. But those
approaches don't really give you very much detail, nor are
they useful outside of the immediate area. If you see
your cows are playing Halo two instead of Uncharted, it
doesn't tell you about the weather that's going on in
(45:43):
the town on the other side of the valley, for example.
And let's say that you want to go to the
other side of the valley because you need to sell
your I don't know yearly parsnip harvest, So for that
you would need more information. You would need someone on
the other side of the valley sending you observations of
their weather phenomena, and also a way of understanding what
those observations mean in relation to that area's local weather.
(46:07):
You would need a meteorologist and some reliable data gathering sensors,
and in our next episode will explore those worlds and
talk about the complex models scientists have created to describe
and predict our weather and to really get a grip
on how impressive it is and why we need supercomputers
to run some of these weather models. Will also talk
(46:29):
about why are there more than one? Why is there
more than one weather model? Wouldn't one weather model work
for everywhere? As it turns out new there are a
lot of different weather models, and they all have different
levels of resolution, meaning some of them have way more
observing stations reporting in for a localized area, which means
you have very very accurate reports of what is happening
(46:53):
in a specific region, but they don't cover a large region,
like a large area might be a section of a country,
but not an entire country, or certainly not a continent.
Then you might have much larger weather models that cover continents,
but they do so at a much lower resolution. You
don't have specific accuracy for independent regions. Ideally, what we
(47:17):
want to arrive at is a global model that can
have incredible resolution down to the local level, so that
we know what the weather is going to be like
in our hometown, we know what the weather is going
to be like in the place we're going to travel
to on the other side of the world, and we
can even see how the weather conditions in one location
(47:38):
are affecting the subsequent locations further down the line. That's ideal.
We are not there yet in our next episode. We'll
talk about why that is. But for now, if you
guys have suggestions for future episodes of tech Stuff, please
let me know what those are, because I hate guessing.
You can write me My address is tech stuff at
(48:00):
how stuff works dot com, or you can drop me
a line on Facebook or Twitter to handle at both
of those is tech Stuff hs W. If you would
like to watch me record an episode live, go to
twitch dot tv slash tech stuff. You can see the
schedule there and you can join in and watch as
we have technical difficulties that extend a forty five minute
(48:21):
long recording session into an hour and a half that
really happened today, and you wouldn't be able to see
it unless you go to Twitch dot tv slash tech
stuff to enjoy and watch as other people pop into
the studio and try and fix problems. It's exciting. I
hope to see you there and I'll talk to you
again really soon for more on this and thousands of
(48:47):
other topics. Because it has staff works dot com
Text with technology with tech Stuff from stuff works dot com.
Hey there, and welcome to tech Stuff. I'm your host,
Jonathan Strickland. I'm a senior writer here with how stuff
works dot com, and today I wanted to talk about
something I got to do. Those pretty cool just last week,
(00:26):
well last week as of the time I'm recording this,
I got to go visit the Weather Company to do
some interviews about meteorology and also ibm s Watson platform.
And it was a really cool experience to actually get
to walk around and see the various people who work
on weather science and try to figure out what was
(00:48):
the weather doing right now and was it going to
do next. I even managed to cause some problems for
the Weather Channel, but that wasn't entirely my fault. Uh
Now to explain us, the Weather Channel and the Weather
Company used to be the same entity, but then IBM
acquired the product and technology divisions of the Weather Company
(01:10):
and they bought those sections, but they didn't buy the
television broadcast business. So now they are two independent businesses.
One of them is run by IBM, the other one
is its own standalone weather broadcast service. That being said,
they still work very closely together. The Weather Channel still
gets a lot of its data and it's information from uh,
(01:32):
the Weather Company, so it's not like they are completely
independent of each other, and they both still exist in
the same building. They both are located out of the
same headquarters building here in Atlanta, Georgia. So there is
a Weather Channel studio that is in part of this building,
and there's the Weather Company offices that's on different floors
(01:55):
of the building, and UH they kind of co occupy
space even though they are no longer corporately speaking anyway
the same entity. So I thought it'd be fun to
do an episode about meteorology and weather models. This is
gonna be a two part episode because I have to
cover the science behind weather first and then talk about
(02:18):
meteorology to let you understand how meteorologists base their forecasts
off of weather conditions. You have to understand the complexities
of whether before you can really get a grip on
what it is that meteorologists do. And so in order
to do that, this episode is gonna be a little
less about tech and more about science in order for
(02:41):
us to have a deeper understanding of meteorology. In the
next episode, I should I should also mention We've covered
this topic in Tangential Ways and Older Tech Stuff episodes,
but it was more than overdue for a revisit. So
that's why we're going to talk about it today. We're
gonna really look at how weather systems actually work. Uh.
(03:07):
And before I get too far, I guess I should
actually explain what I meant when I said I caused
some problems for the Weather Channel. So while I was
at their headquarters, I was getting ready to shoot a
video interview with a man named Dale Eck, who is
the director of the Weather Forecast Center for the Weather Company.
(03:27):
So this guy is the head meteorologist in charge. He's
been doing work in meteorology for thirty years, and he
has a desk that's very close to the broadcast studio
for the Weather Channel. The broadcast studio has glass walls,
so you can see right through the walls. If you
ever watch a broadcast on the Weather Channel and they
(03:47):
shoot from inside the studio, you'll see people walking in
the background. You'll see desks and monitors and lots of
of colorful imagery because people have got a lot of
weather maps up in the background, so all of that's real.
Those are the actual people who work at the company. Uh,
and that's where we were shooting our videos. We were
(04:09):
shooting off to one side of this studio, and while
we're getting ready to shoot, we had set up the camera.
I was miked. We had a shotgun mike so that
we can pick up Mr X his his contributions. We
were off to one side of the studio, so we're
up against where the glass walls are, but we weren't
(04:32):
directly across from where the cameras were set up. Um,
they did have sets where they could pivot around where
we would have essentially been in the background for those
those shots if they had set something up, but they
were mostly shooting directly against the back wall of the
studio and we were on one of the sidewalls. So
we're getting ready to shoot, and one of the the
(04:55):
employees over at the Weather Company very helpfully pointed out
a bank of light switches that were in control of
production lights. So flipping those switches would turn several lights
on in the area we were standing in That would
end up providing a lot more light for our video,
and that is really important if you're shooting video, you
(05:17):
need good lighting. So after being told about them, we
turned them on. We being my producer, turned them on,
and you know, he was essentially told to do it,
so that's what he did. And it didn't take very
long before a floor manager for the Weather Channel, very
calmly walked up and asked us to knock that off.
(05:38):
Although I should say she was incredibly friendly and professional.
She wasn't mean about it at all, but explained that
the light that we had created was bleeding into the set.
You know, it's a glass wall, lights just passing right
through it, so it was affecting the shot for the
actual Weather Channel, you know, the nationally televised Weather Channel broadcast.
(06:03):
So my little YouTube video that I was shooting was
impacting a nationally broadcast television scene. So that was a
little bit of a Oopsie Daisy moment for me and
my team. The nice thing is it was probably pretty
subtle and it probably didn't have that big of an
(06:24):
impact at all, but still it made us feel like
we were kind of jerk faces. And if you were
watching the Weather Channel last week or this would that
would have been, um, you know, this is June right now,
so it would have been June Thursday. If you were
watching the Weather Channel, you know, trying to keep up
(06:47):
to date with Tropical Storm Cindy, and you were wondering,
why is the lighting going all crazy in this broadcast?
That was us are bad, But I have to really
thank everyone who works for the Weather Channel and the
Weather Company. They were very generous with their time and
(07:08):
they gave us lots of leeway to shoot really cool video.
So it was a great visit and it helped me
appreciate the complexities of meteorology on a deeper level. So
let's now talk about weather forecasting. It's an interesting business.
At a very very high level, like a super simplistic level.
(07:31):
Weather forecasting, at least in the recent past, involved taking
lots of observations, comparing those observations of present conditions to
things that had happened before in the past, researching what
followed those similar conditions when they did happen before, and
then making a guess as to what is going to
(07:51):
happen next based upon past experience. That's a drastic oversimplification,
and really it's saying that it's about pattern recognition, and like,
let's say, if you notice that when the temperature goes
up at a certain time of day, with these other
factors in place, the chance of rain increases drastically based
upon past experience. You might use that to help forecast
(08:15):
the weather and say there's a good chance that's going
to rain later today because these other factors are at play,
and other times when that has happened, it's rained. But
let me give you a more simple example about how
this might work out. Let's say you've got some basic
meteorological gear, like some sensors, a barometer, wind speed, indicator,
(08:39):
wind direction. You know how much humidity is in the air.
You know the temperature because you've got a thermometer, all
these sort of things. These are the typical sensors you
would find at a weather observation point. You've kept a
log book of weather for this particular location that goes
back two decades, so you've got twenty years of information
(09:01):
at your disposal, twenty years of collections of data points
and what was actually happening with the weather. You make
your observation in the morning, you note the temperature, the
air pressure, You've got all these different factors, and then
you look at your log books and you look for
days that are similar to the conditions you are currently observing.
(09:27):
Then you look to see what happened later on those
previous days. So if you had one hundred mornings that
are similar to the conditions of the morning you are
concerned with, like this morning, you wake up, this morning,
you take readings, you find one other, one other examples
in your log book that are similar to today, and
(09:47):
then you notice that on seventy of those one days
it rained. You could say there's a seventy chance of rain.
That seventy of the time, when conditions were the way
they are right now, it rained. Of those days where
the conditions were exactly the way they are right now,
it did not rain. And I don't really mean exactly.
(10:10):
I guess I should say approximately, because weather is incredibly
complicated and to have two weather systems behave exactly the
same way under the same circumstances is pretty unlikely. But this,
again is a drastic oversimplification of how weather forecasts work.
(10:30):
It does give you a basic idea of the the
principle behind meteorological forecasts, at least until more recently we
get into weather simulation and huge amounts of data processing.
Today that gets a lot more sophisticated than just what
are the conditions today and what happened on previous occasions
(10:52):
when those conditions were present. But keep in mind meteorology
is constantly evolving. It has ever reached a perfect level status,
as anyone who has depended upon a weather forecast knows,
you've probably in the past looked at a weather forecast
and said, oh, there's no chance of rain, and then
a thunderstorm pops up. Well, that's because weather is really
(11:15):
complicated and sometimes a hyper local event can occur that
is impossible to really predict when you're looking at, say
a regional weather forecast, because your fidelity doesn't get that small.
You can't predict everything that happens within that region with
perfect accuracy. You're giving more of an overall look for
(11:37):
the region as a whole. So it gets really complex.
There are a lot of different variables, and there's a
lot of different technology that goes into gathering the information
about those variables and then crunching those numbers to make
some meaning out of it, which is why it's an
ideal topic or text stuff. Now, if we are to
(12:00):
understand really how meteorology works, we've we've got to take
a deep looking at a look at whether or not
a deep looking that makes no sense, but a deep
look at whether. We at least need to get as
deep in understanding for whether as we can in a
casual podcast setting. So the first step is acknowledging the
difference between weather and climate. This is important because I
(12:23):
see these two concepts conflated all the time, and frequently
it pops up in in political discussions because you have
people with agendas who want to push specific action items
that favor their philosophy over the action items of people
who oppose their philosophy. And frequently in those discussions, people
(12:47):
will start to make generalizations about weather and climate that are,
if not untrue, at least inaccurate. So let's settle that.
And I know all of you know this, but it's
good to at least start with the baseline. So whether
(13:07):
refers to the current state of the atmosphere, it's it's timely.
It's either something that's happening right now, like you're talking
about the weather right now, you're talking about a weather forecast.
You're talking about something that's going to happen within the
next day to ten days maybe or maybe a little
further out, but that's about it. Or you're talking about
what has happened over the past few days, but that's
(13:29):
about it. Like it's about a month or so of
time stretching backward and forward uh in total from where
you are right now, So it's very timely. Climate, however,
is about whether patterns over vast spans of time or
at least several years, if not decades of time. So
(13:50):
climate is more about general weather patterns and how they
behave over these these uh the span of years. So
climate change is very gradual. That means that you're not
likely to notice climate change on a day to day basis,
which means that if you use an argument like global
(14:13):
warming isn't real because it's snowed last winter, that's a
fallacious argument because you're talking there about whether not climate
climate would be a gradual change, which over the course
of several years might mean that after several years it's
snowing less and less, or the snow is not lasting
(14:33):
very long, the the period of time where it does
snow is decreasing, like it's becoming more concentrated in a
narrower span of days. Those are the sort of things
we might see as a result of climate change over
the course of several years. But we humans aren't very
good at conceptualizing that. We tend to focus on stuff
(14:55):
that we've recently observed, but particularly when it's something that's
happening at at times. So if you were to have
an unusually mild summer, you might think, well, that says
that climate change is is bogus because I should it
should be much hotter than that. That's not taking into
(15:15):
account the long term changes in trends. So again, climate
is the long view, whether is what is happening right now?
Now that we've established that, we can get past those
weird straw man arguments people make that tried to discredit
(15:36):
one another for whatever philosophy they have using weather in
place of climate, it just doesn't work. Climate change, by
the way, is a real thing. Uh, it is a
scientific consensus has found that climate change is real and
that humans have had an impact, a significant impact on
climate change. And consensus is no small matter getting scientists
(15:59):
to agree to some thing. That's I mean, science is
all about questioning claims and putting them to the test.
That's how science works is you make an observation or
you make a prediction, and then you test it over
and over and over again to see if it holds true.
If you get to a scientific consensus where a lot
of scientists, the vast majority of them all agree on something,
(16:20):
that's a powerful statement, although we often will see that dismissed.
Uh So, again, this isn't to get political. This is
just stating a scientific fact, not a political effect. Climate
change is real, humans have an impact on it. What
does that mean politically, Well, that's a totally different discussion.
(16:41):
So there's probably people out there who wish that climate
change wasn't a real thing, that this was all just
a manufactured story. But if wishes were horses, beggars would ride.
As my old social studies teacher would say, So, climate
describes weather trends over many, many years, and weather describes
changing atmospheric conditions on a much shorter time span. And
(17:03):
our atmosphere is where weather happens. Again, not a big shock.
This is elementary school science. It's made up of a
lot of gases our atmosphere. The big one, of course,
is nitrogen, that makes up about of the atmosphere. Then
comes oxygen, which is my personal favorite. I'm totally breathless
(17:23):
without oxygen. It makes up about of the art's atmosphere,
and then you've got less than a percent of argone
point zero three carbon dioxide, and the rest of it
is made up of small amounts of water, vapor, hydrogen, ozone, neon, helium, crypton,
and xenon. Our atmosphere is pretty thick, and there's not
(17:47):
really a hard barrier between the top of the atmosphere
in the beginning of space. It's kind of a fuzzy barrier,
and there's not like you can't point to a specific
height above the Earth and say, specifically, at this point
the atmosphere ends, and this is just empty space beyond it.
The best you can do is do an estimation. So
(18:09):
generally speaking, the atmosphere pretty much peters out into nothing
once you reach about six hundred miles or one thousand
kilometers above sea level, So you gotta go at sea
level six d miles up and you're pretty much at
the point where you're not going to find any molecules
of any significant number that represent an atmosphere. Gravity holds
(18:33):
the gases down to the planet, which I'm sure seems
pretty obvious. Without gravity, the atmosphere would dissipate into space,
but don't worry, so would we. So the gases wouldn't
be lonely for very long. It's a moot point because
we do have gravity, so we're good. The atmosphere is
also a very heavy thing. Collectively, if you take all
(18:55):
of the other's atmosphere, it weighs five point five quadrillion uns.
That's four point nine nine quadrillion metric tons. Again, that's collective.
That's all the atmosphere that surrounds our planet. Obviously, you
are not walking around with a few quadrillion tons of
weight on top of you. This weight of the atmosphere
(19:17):
creates atmospheric pressure. The pressure is different at various altitudes,
which makes sense. If you are on top of a mountain,
you actually have less atmosphere above you, like there's less
air between you and outer space. If you're on top
of a mountain, then if you were standing in the
middle of a valley, there would be more air between
(19:38):
you and outer space. Because again remember we're measuring that
by sea level, so your altitude makes a big difference.
You would have a lower atmospheric pressure at a high
altitude than you would somewhere with a low altitude. The
pressure also compresses the gases in the atmosphere, so air
closer to the surface of the planet is more dense
(20:00):
than air that's near the edges of space, and all
the weight above that low altitude air is forcing the
various molecules to get all chummy with each other. So
you've got denser air closer to the surface. So I've
got more to say about atmospheric pressure and it's rolling
weather in just a minute. But before I jump into that,
(20:21):
let me take a breath and thank our sponsor. All right,
So let's say you are at sea level. The average
atmospheric pressure at sea level is fourteen point seven pounds
or six point seven kilograms per square inch. As you
(20:42):
climb in altitude, the pressure and density of the air
around you decreases until you reach a point where it
would be quite difficult to breathe, and you need to
breathe in more in order to get enough oxygen so
that you can continue, you know, living. So you might
take a lungfull and not get enough oxygen to remain
(21:03):
conscious if you're at a high enough altitude, which is
part of the reason why mountain climbers have to tackle
really tall mountains and stages. They have to have camps
where they take a break and acclimate to the lower
air pressure and lower air density of higher altitudes. So
gravity obviously plays a big part in weather systems keeping
(21:24):
our atmosphere nice and in place. The Sun obviously also
contributes to our weather patterns. The Sun is the direct
source for most of the energy here on Earth. Some
of the energy of the Sun gives off warms our
atmosphere directly, but most atmospheric warming actually comes not from
sunlight coming down to Earth, but rather the heat that
(21:45):
is radiated off of Earth. The heat that the Earth
has absorbed from the Sun. So the plant itself absorbs
heat and then releases that heat later on. That tends
to be what heats up most of the atmosphere. The
reason this happens is because the type of radiation that
we're talking about radiation from the Sun is short wave
(22:06):
radiation that easily passes through the gases the atmosphere and
then it gets absorbed by the planet. When the planet
emits heat, it's emitting long wave radiation. Long wave radiation
gets absorbed readily by the atmosphere, so the atmosphere warms
from the ground up. And that also explains why if
(22:28):
you were to climb a mountain as you would climb
in elevation, the temperature would decrease to a point anyway
in the troposphere. So there are four layers of Earth's atmosphere,
and you classify those four layers by temperature ranges. The
layers aren't uniform. Their thickness varies a bit as you
(22:50):
go from region to region around the Earth, but they're
roughly outer shells of Earth. The innermost one is the atmosphere,
as the level closest to the surface of the Earth.
It ends somewhere around seven miles or eleven kilometers above
sea level on average. Throughout the troposphere, as you climb altitudes,
(23:12):
the temperature drops. That's one of the markers for the
troposphere that all stops when you pass the tropo pause.
That is the boundary between the troposphere and the stratosphere.
That is the next layer out from the troposphere. The
tropospheres where all of Earth's weather happens. It also accounts
for eighty percent of the air in our atmosphere. The
(23:35):
other three layers contain the remaining twenty of the air
in our atmosphere. Now, remember our atmosphere extends all the
way up to six hundred miles above sea level, whereas
the troposphere ends at seven miles above sea level. So
within those first seven miles out of six hundred, you
(23:56):
have eighty percent of the air in our atmosphere. That
tells you how densely packed those gases are. The stratosphere
extends from the tropopause up to about thirty miles above
sea level or forty eight kilometers. For the first few miles,
the temperature of the stratosphere remains pretty stable with regards
to the tropopause below. So remember you climb up through
(24:18):
the troposphere, the temperature starts to go down. When you
hit the tropopause, the temperature pretty much stabilizes, and then
you're in the stratosphere and the temperature remains stable for
the first several miles, but then the temperatures actually start
to increase. It starts to get warmer as you move
through the stratosphere. This is because at those upper levels
(24:39):
of the stratosphere you can find ozone. Ozone can absorb
ultra violet radiation from the Sun. Unlike most of the
other gases, it actually can absorb some of those short
wave radiations. So the ozone heats up, which means the
upper levels of the stratosphere are also warmer than the
lower levels. Above the amosphere is the miso sphere, where
(25:02):
temperatures decline again, getting to be the coldest temperatures in
Earth's atmosphere. Those temperatures hovered around minus degrees fahrenheit or
minus nineties celsius. And the final layer of the atmosphere
is the thermosphere, which shares its outer body with space,
and the air here is not dense at all. It's
(25:24):
actually pretty widely spread out. The molecules are very thin like,
it's very thinly populated, the opposite of very dense. In
other words, the interesting thing here is that the thermosphere
technically gets really freaking hot. We're talking like degrees fahrenheit
(25:44):
or shundred degrees celsius. But because those molecules are so
few and far between, it would not feel hot to
you because you wouldn't be in contact with these highly
energized molecules. They're spread too far apart from each other.
It's kind of like being inside and an enormous arena
stadium and there are a dozen ping pong balls flying around.
(26:05):
The Odds of any of those ping pong balls actually
making contact with you are pretty low. Because you're in
a big area with these tiny things moving around, it's
just not likely that you're gonna encounter one of them.
Same thing is kind of true with molecules out in
uh the the thermosphere. So while those molecules will be
quite warm and you're not likely to run into them.
(26:28):
Now back here on the surface, where we have the
troposphere to deal with, you've got atmospheric pressure, you've got temperature.
These two factors affect atmospheric movement. As gases heat up,
the molecules in those gases move around more, they spread out,
they become less dense. When the density changes enough so
that the air above is more dense than the air below,
(26:52):
that denser air is going to sink down and displace
the warm air that is there. You might have heard
the phrase warm air rises, Well, it's true, but it's
really probably more accurate to say cold air sinks. If
you were to have a very dense fluid and you
put it on top of a less dense fluid, you'd
(27:12):
see the dense fluids sink down to the bottom and
the less dense fluid would rise to the top. Same
thing is true with atmospheres and our atmosphere is a fluid,
so these denser, colder areas sink down and that pushes
the warm air up to the top. So this way
you get some fluid movement in our atmosphere as different
(27:34):
areas start to warm up or cool down. Now, as
that warm air does rise, it actually starts to cool
down because it's going up in altitude. And remember and
those altitudes in the troposphere. The higher you go, the
cooler it gets. So the warm air initially gets pushed
up by colder air, but then the warm hair itself
begins to cool and it has a tendency to sink again. Now,
(27:56):
if everything we're equal, if our planet did not rotate,
if we didn't have any uh variation in parts of
the plant that warmed or cooled, if it all warmed
or cooled at the same time, our atmosphere behavior would
be really simple. It would expand when sun was hitting it,
(28:17):
and it would contract when the sun wasn't hitting it.
So you would just see the atmosphere kind of breathe
that would move out and in based upon the warming
and cooling, and that's all it would do. You wouldn't
get a whole lot of other movement there, but that's
not our reality. The reality is we have a lot
of other factors at play that create the the conditions
(28:39):
that allow wind to generate. So regions of the Earth
warm at different rates at different speeds, and thus regions
of our atmosphere end up warming at those different speeds,
and that regional variation causes a lot of churning in
the atmosphere, which creates pressure differentials between regions, thus leading
(29:00):
to wind. So let's take a city and countryside example
to kind of understand what I mean by this. If
you have a city, the city heats up faster than
the countryside would during the day due to a lot
of the materials in the city, you know, concrete, blacktop,
these sort of materials soak up a lot of heat,
so they're going to get much warmer than the countryside wood,
(29:21):
which doesn't have those sort of materials all through it.
So you've probably heard of the island effect, which is
where you get an island of heat because you've got
a bunch of of mass that just absorbs heat readily
in one space, and it creates an island effect within
the region. That's what we're talking about here. The city
(29:42):
ends up soaking up a lot of heat and then
releases that heat. Over the course of many hours. As
cities radiate heat, that heat warms the atmosphere that's surrounding
the city's That warm air is less dense than the
cold air that's further on the outskirts of the city,
out in the countryside, So the warm air is an
area of low pressure because it's less dense. It's actually
(30:04):
exerting less pressure on the city because it weighs less.
It is less dense than the cold air that's around it,
or the relatively cold air compared to the city's air.
So the cold air blows into the city because it
wants to move from an area of high pressure to
an area of low pressure, sort of that. In tropic movement,
the warm air is forced upwards in an updraft and
(30:29):
starts to climb up into the upper levels of the troposphere.
As it does so, it starts to cool, and once
it cools enough, it needs to come back down. But
because cities soak up so much heat, and because the
updraft can be so powerful, the cold air can't just
sink back down to where it was. It actually has
to move outward and then sink down further out from
(30:51):
where the city is. It's almost like a fountain. You
would see the water of the fountain come up in
a column and then spread out in a fan the
top and come back down to the base of the fountain.
That's sort of what's happening, except with atmosphere, not with water,
although it could be with water. We'll get into rain
in just a second. So at night the city would
(31:13):
cool faster than the countryside does, and then the trend
would reverse itself. We would have winds that are originating
essentially from the city moving out to the countryside. This
little system is what we would call a convection cell,
and convection is when the movement of mass or circulation
of atmosphere transfers heat through some sort of substance. In
(31:34):
this case, we're talking about the planet and the atmosphere.
On a larger scale, forces affect these movements to generate
massive weather weather patterns. The poles are areas of high
pressure and the equator is an area of low pressure.
You've got a lot warmer air moist air in the equator,
a lot cold or dry air over at the poles.
(31:54):
And if that was all there were to it, we
would see winds coming from the north and south and
converging towards the equator. But there are a lot of
other areas of high and low pressure across the surface
of the Earth. It's not just the polls and the equator.
There's a lot of variation there due to tons of
different stuff, including topography like mountains and valleys, that sort
(32:15):
of thing, deserts. So you have lots of areas of
high and low pressure across the surface of the Earth,
which creates natural pressure gradients, and that generates wind. Wind
from high pressure areas cycle inward to low pressure areas.
In fact, we call a low pressure center a cyclone.
Now it's not the same thing as cyclones that are
(32:36):
also known as hurricanes, slightly different, although there is a
circular motion to it. That's where you get that cyclone
name there. High pressure centers are anti cyclones, as an
anti not as an anti cyclone the sister of my father,
who we don't talk about. It's a different thing entirely.
(32:58):
High pressure air moves in a down undraft as low
pressure air moves in an updraft, and Earth's rotation also
gets into the game. This is where we get the
Coriolis effect. In the northern hemisphere, wind deflects towards the right.
In the southern hemisphere it's deflected to the left. The
Coriolis effect really influences large fluid masses, by the way,
(33:18):
so it does not necessarily affect which way the water
goes down a sink or a toilet, despite what the
Simpsons would have you believe. Uh, there are a lot
of other smaller things that can affect the way water
drains down the drain and is not the Coriolis effect.
Coriolis effect is really for very big systems, not for
small systems like a a sink full of water or
(33:42):
a tub full of water. But the Coriolis effect does
break the two big convection cells that otherwise would exist,
you know, the ones that would be the North and
South hemispheres, and it ends up creating three different types
of convection cells. You get two of each type. You
have two polar cells to Hadley cells, and two Feral cells.
(34:05):
And the Hadley and Feral cells are named after meteorologists
who discovered them. This is the important thing, really is
to remember that these convection cells have a really big
impact on on larger weather trends, global weather trends now
where the wind blows down here near the surface, air
encounters resistance in the form of friction, but a bit
(34:27):
higher up in the atmosphere that's not a problem. So
jet streams shoot around at fairly high altitudes we're talking
twenty thoty five thou feet or between six and fourteen kilometers,
and they don't encounter this friction. They move it incredible speeds.
They can carry temperature changes effectively around the world. So
you'll see things about jet stream and how that will
(34:48):
affect local weather patterns depending upon where you live. High
altitude winds, the coreolas, affected pressure gradients are the three
big influencers of wind generation on a global scale. But
remember regional geography, coastlines, mountains, valleys, all of that also
has an effect. Regional heating and cooling has an effect.
(35:09):
So these big factors are the major variables, but they're
not the only ones. And now you're starting to see
all the complications that come into just describing weather, let
alone predicting it. But that covers wind. Rain is pretty
easy to explain. The water cycle on Earth is pretty
(35:31):
much a closed system. Water evaporates into the atmosphere. Water
vapor condenses as it cools down, so it condenses from
water vapor and turns into liquid water. It starts to
cling to specs of stuff in the atmosphere, little particles
of dust. Uh. That ends up becoming the nucleic sites
for rain drops. If it is able to accumulate enough
(35:51):
water vapor. The cooling happens. Once water vapor rises high
enough into the air, and with enough cooling water vapor,
you get clouds. Wind will push and reshape the clouds,
moving them to different locations. And if you get enough
water vapor condensing around those nucleic sites, it becomes too
heavy to remain aloft by the winds alone, and it
(36:13):
starts to fall. And that's when you get rain, or
if it's really cold, you might get sleet or freezing
rain or snow. But you get what I mean, you
get precipitation. I've got a little bit more to say
about the water cycle and other elements of weather, but
before I jump into that, let's take another quick break
and thank our sponsor. So water vapor can be pushed
(36:44):
into higher altitudes through several different ways. One of those
is just changes in elevation in the land. So if
you have a warm air system and it's got a
lot of water vapor in it, and it moves across
flat lands and start to encounter mountains, it has to
conform with the topography, so as it gets pushed against
(37:08):
the mountain, it actually starts to go up the mountain,
and that means some of that water vapor gets pushed
up to higher elevations and it gets high enough, then
it can cool down, condense, turn into clouds, and eventually
even turn into precipitation. So if you've ever heard about
windward and leeward that's what this refers to. The windward
(37:28):
side of a mountain is the side that faces the
area where wind comes in from. So traditionally the direction
front which fronts move through, so you have a warm
air mass coming through to a hit a mountain, that's
the windward side. The leeward side tends to be gloomy
and covered in rain a lot because that water vapor
(37:49):
that hits the windward side gets forced upwards into the
higher parts of the atmosphere or of the troposphere i
should say, condenses into uh into clouds, and then eventually
can turn into rain or precipitation of other forms, and
on the leeward side that's where you get that rain,
and you also have a lot of cloud cover. So
there's a sunny side of a mountain and there's the
(38:11):
less sunny side of the mountain. Typically, and uh, that's
one way water vapora can be pushed into high altitudes
to form clouds. But there's also an way called frontal wedging,
which originally I thought was something that happened to me
back in middle school, but it turns out I was
thinking of something totally different. This is actually when warm
air ends up colliding with a cold air mass, and
(38:35):
the cold air mass sort sort of acts like a
ramp because remember a cold air is more dense than
warm air, so warm air is going to float above
or rise over cold air. It ends up being wedged
on top of cold air. That pushes warm water vapor
up into those higher altitudes again where it can condense
(38:55):
and form clouds. So if you have a warm air
mass moving into to a cold front, or rather a
cold air mass, not a cold front, then this can happen.
The warm air will rise over the cold air, the
water vapor in the warm air will slowly condense and
then you end up getting clouds as a result. This
is typically what we call a front. So a warm
(39:17):
front is when warm air moves into an area that
has cold air in it. A cold front is when
cold air moves into an area that has warm air
into it. So essentially it's a low pressure system moving
into a high pressure system, or a high pressure system
moving into a low pressure system. And then you've got
these masses colliding with one another. Really, it just depends
(39:37):
on what type of air mass is moving in and
what type of air mass is currently in the region.
That determines whether it's a cold front or a warm front.
But then you also have two other types of fronts.
You have a stationary front, and these cases you have
two air masses that are unable to advance against each other.
They kind of just bump up against each other and
(39:59):
stay there. And then you have the occluded front. This
is when a cold front moves fast enough to overtake
a moving warm front. So that's another way that water
vapor can be pushed up into the higher elevations. Way
number three for water vapor to go moved moving up
to those higher altitudes is called convergence. Now this is
(40:19):
not the same type of convergence I typically like to
talk about here on tech stuff. It's when two similar
air masses collide and both end up forcing air into
an updraft, which includes water vapor. And so yet again
we see water vapor get pushed up and cooling down
to condense. But that's convergence. And finally you have what
(40:40):
is called convective lifting. This is a localized effect, so
it's not something that happens on regional or global scales,
but rather very local scales. It's when Earth's radiation of
heat causes a pocket of air to warm and rise,
forcing water vapor up in the process and creating clouds.
This requires having an area that is absorbing a lot
(41:01):
more heat than its surroundings typically do. So a good
example might be a large airport. The airport's got a
lot of surface area that gets exposure to the sun.
It absorbs a lot of heat, much more heat than
the surrounding area typically does, and so it releases more
heat and as a result, you can get cloud formation
above airports just because of this localized convective lifting. So
(41:24):
now we understand the general principles behind weather that air
pressure temperature and the presence of water vapor matter a lot.
Now other things matter too, of course. The Earth's access,
for example, is that twenty three and a half degrees tilt,
which means we're likely, uh, we're we're we're like, we're bobbling,
bobbling around like a wobbly top as we orbit the Sun,
(41:45):
and this causes different parts of the planet to receive
more or less sun exposure during certain parts of the year.
That ends up affecting weather patterns and seasonal patterns and weather.
It's complicated in that incoming systems can have a dramatic
effect on systems that are already within a region. So
it's an enormous, chaotic mess with lots of variables, and
(42:05):
that's part of the reason why meteorology is so darned challenging.
We cannot isolate those variables. We cannot really understand how
to properly weight all of them in every situation. That is,
determining which variables are most important under any given set
of circumstances, it's really really hard to do. So you
(42:26):
might say that under a certain set of conditions, the
temperature of the air is the most important variable, and
that depending upon that temperature of the air, certain outcomes
are almost absolutely gonna happen, right But then you might say,
under slightly different circumstances, temperature no longer becomes the most
important variable. Now it's air pressure that's more important than temperature.
(42:50):
Weather is so complicated, and there's so many different variables
that have different weights and different situations that it becomes very,
very difficult to understand what is happening right now, let
alone predicting what is going to happen. In fact, I
find it amazing that we can manage to have any
real accuracy and weather predictions at all, because it's so
(43:10):
crazy complicated. Now, Before I wrap up, I thought it'd
be fun to talk about some of the earlier forms
of weather forecasting before you know, sensors and and observing
stations and computer models came along. The stuff we used
to do before we had all those sophisticated technologies and
really a truly astonishing amount of processing power capable of
(43:34):
handling all those points of data simultaneously. Because we humans
have been trying to suss out weather for centuries, knowing
what the weather will be like has a tremendous impact
on our decisions like should I buy tickets to that
outdoor sporting event, or how can I plot a course
for these shipping goods to get from point A to
point B with the least amount of delay and fuel consumption.
(43:55):
But our methods for making predictions haven't always been terribly scientific,
and it's heart a lot of our weather predictions were
centered on pattern recognition. That's what I alluded to at
the top of this episode. We would say, hey, remember
that other day that was a lot like today. Well,
it rained like a son of a gun later on
the evening, and that other day, I bet that happens
(44:16):
again tonight. I bet we get more rain tonight, because
that's what happened that other day. Early human civilizations made
similar observations and predictions, which range from the immediate, which
would involve something like I better seek shelter because it
looks like it's going to storm, to more long term planning,
such as I've noticed that the weather seems to get
warmer for a while, and then everything is growing, and
(44:38):
then after a while the weather starts getting cold and
everything stops growing. So maybe I should grow stuff in
this one part of time and harvest stuff at this
other part of time. In other words, we started learning
more about how seasons work. There are some changes in
conditions that are a bit too subtle for humans to
pick up on them by themselves, but they're are other
(45:00):
animals that are more sensitive to those changes, things like
atmospheric pressure, for example, and so humans would sometimes observe
changes in animal behavior that would precede certain types of
weather events. Those behaviors would become associated with weather, leading
to some folk knowledge about what it means when your cow,
I don't know, switches from Xbox to PlayStation. I guess
(45:23):
I should point out right now that I haven't been
on a farm in like thirty years, so my understanding
of animal behavior might be a little off. But those
approaches don't really give you very much detail, nor are
they useful outside of the immediate area. If you see
your cows are playing Halo two instead of Uncharted, it
doesn't tell you about the weather that's going on in
(45:43):
the town on the other side of the valley, for example.
And let's say that you want to go to the
other side of the valley because you need to sell
your I don't know yearly parsnip harvest, So for that
you would need more information. You would need someone on
the other side of the valley sending you observations of
their weather phenomena, and also a way of understanding what
those observations mean in relation to that area's local weather.
(46:07):
You would need a meteorologist and some reliable data gathering sensors,
and in our next episode will explore those worlds and
talk about the complex models scientists have created to describe
and predict our weather and to really get a grip
on how impressive it is and why we need supercomputers
to run some of these weather models. Will also talk
(46:29):
about why are there more than one? Why is there
more than one weather model? Wouldn't one weather model work
for everywhere? As it turns out new there are a
lot of different weather models, and they all have different
levels of resolution, meaning some of them have way more
observing stations reporting in for a localized area, which means
you have very very accurate reports of what is happening
(46:53):
in a specific region, but they don't cover a large region,
like a large area might be a section of a country,
but not an entire country, or certainly not a continent.
Then you might have much larger weather models that cover continents,
but they do so at a much lower resolution. You
don't have specific accuracy for independent regions. Ideally, what we
(47:17):
want to arrive at is a global model that can
have incredible resolution down to the local level, so that
we know what the weather is going to be like
in our hometown, we know what the weather is going
to be like in the place we're going to travel
to on the other side of the world, and we
can even see how the weather conditions in one location
(47:38):
are affecting the subsequent locations further down the line. That's ideal.
We are not there yet in our next episode. We'll
talk about why that is. But for now, if you
guys have suggestions for future episodes of tech Stuff, please
let me know what those are, because I hate guessing.
You can write me My address is tech stuff at
(48:00):
how stuff works dot com, or you can drop me
a line on Facebook or Twitter to handle at both
of those is tech Stuff hs W. If you would
like to watch me record an episode live, go to
twitch dot tv slash tech stuff. You can see the
schedule there and you can join in and watch as
we have technical difficulties that extend a forty five minute
(48:21):
long recording session into an hour and a half that
really happened today, and you wouldn't be able to see
it unless you go to Twitch dot tv slash tech
stuff to enjoy and watch as other people pop into
the studio and try and fix problems. It's exciting. I
hope to see you there and I'll talk to you
again really soon for more on this and thousands of
(48:47):
other topics. Because it has staff works dot com
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