Without the Sun: Episode 9-Controls on Temperature


Uploaded by geoscienceEIU on 17.10.2011

Transcript:
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In this video lecture, I'm going to teach you the
five controls on temperature, and they're quite simple.
They are the, these objects, or these types of locations, have
an influence on temperature.
The first one is latitude.
Latitude has an influence on temperature.
If we start at zero degrees north and south, which is the
equator, and we go north to 30 and then to 60 and then finally
to 90, it gets progressively colder, and that coldness, it
gets cooler as we go from zero, the tropics, to the 30 degrees
north, to 60 degrees north, and then finally we get to extreme
cold at 90 degrees north.
So each of these temperatures change according to latitude, so
this is a temperature change by latitude.
The next control on temperature is altitude.
Altitude is the change in height, so if we have here a
valley and then we have mountains, if we have a person
that stands here with a thermometer and then we have a
person that stands here with a thermometer and I place the sun
here, let's consider what is the temperature going to be, the
relative temperature for the valley.
Is it going to be warmer, or cooler than the mountain top,
the answer would be that this is going to be warmer.
This valley will be warmer than this, and the reason is, even
though the person here standing with a thermometer is closer to
the sun, look at the amount of space that you have from here to
here, there's great deal of surface area.
And the surface area is absorbing all the solar
radiation, therefore, it's going to continue to be warmer than
this location which has a very small surface area.
So mountain tops have a small surface area, and if you really
think about it, remember these?
They have ice caps on the tops of mountains.
We are further away from the massive landscape
at the bottom of the mountain.
So this is kind of a very small point topographically speaking,
compared to this.
So the closer that you are to the sea level, you will get a
warmer temperature.
And as you go up in altitude, that temperature decreases
because you're getting away from that vast landscape that is
doing all the absorbing of the solar radiation.
The next control on temperature is continental versus marine
environments.
Continetal versus marine environment.
If you have a location that is, well if you have a location that
is in the middle of the continental area, let's say here
is Fargo and in several miles, several thousand miles, you have
the ocean and you have a city that's here in the ocean, near
the ocean, which one is going to be the most extreme environment?
Is it going to be Fargo?
Or is it going to be Boston?
Well let's consider this, when we have moisture, the
temperature drops slightly.
When there's moisture available, then the temperature comes down
a little bit.
If there is no moisture, then the temperature
wants to go higher.
So if we consider Fargo, there is no vast body of water out
here, so you might get a 95 degree temperature that is the
maximum for the year and then during the winter you get a
negative 20 degree difference which is the minimum in winter.
So this is a great change, a variation in temperature.
On the other hand, you have Boston, you know it might be 90
degrees is the maximum for the year, and perhaps we get a 65 as
a low, now that's optimistic enough, so let's say we'll get
20, 20 minimum.
These are just hypothetical numbers, I'm just throwing these
numbers to show you differences.
So here you get a great extreme in temperature, here you get a
less extreme in temperature.
The reason why this is less is because it
is located near water.
This has an extreme environment, and extreme temperature change,
variation, because it is experiencing continentality.
Continentality, when you have, like St. Louis, St. Louis is in
the middle of the continent, Fargo is in the middle of the
continent, Denver is in the middle of the continent, so you
get this continentality effect when there
is absolutely no water.
With no water I mean significant bodies of water to control the
temperature, so that's why it gets very hot in summer and gets
very cold in winter.
On the other hand, other environments that are along the
coast, have less extreme temperature change, or less
variation because they're near bodies of water.
Now let me explain how this all works.
We'll take two environments, we'll take
our neck of the woods.
You have an urban environment, which is made of asphalt,
concrete, glass, metal, and those kinds of objects, there's
very little green space, so you get a
high temperature in the city.
On the other hand, you get an area outside the city, the rural
area which has trees, it's got plenty of grass, sometimes
you've got crops, you've got corn growing and beans and
various other crops that are growing.
So you have vast amounts of green space.
The temperature in the country might be,
compared to the city, lower.
The reason why you have differences in these two
environments that are relatively close to each other, you have
latent heat.
Latent heat is down, is low, because there's no water stored
in the soil because there's no exposed soil, and I'll get to
the definition of latent heat momentarily.
In the country, the latent heat is very high because in the soil
you have enough moisture stored, it's exposed, the soil is
exposed, it stores the moisture a little better.
So you have moisture storage, moisture that is stored in the
soil, and you have no moisture in this environment.
So the temperature goes up.
And I'll explain in a different way how this all works too.
Latent heat, latent heat is the stored heat energy.
It is heat that is stored, it is hidden.
The reason why it's hidden is because there's moisture
somewhere for that evaporation to work.
So instead of releasing heat, it is pulling in the heat,
therefore you get a lower temperature.
If you consider sweat on your skin, if you have sweat on your
skin, and a breeze blows across it, how do you feel?
You feel cooler, because there's latent heat going on, there's
evaporation.
The heat is being stored in order to evaporate.
Now, another way to explain this is the process
of how heat is emitted.
Does heat emit if latent heat is high?
Now let's have a look at an airplane that flies over the
urban center and then flies over the country.
Alright we have an airplane that flies over both environments.
Now as we said before, the temperature is high over the
urban environment because latent heat, LE the abreviation of
latent heat, is low.
On the other side of this, temperature over the rural
region is low because latent heat is high.
So what do we expect?
Where will there be turbulence?
Turbulence will be experienced over the urban area and smooth
out over rural areas.
The reason why, if you have no surface moisture, latent heat is
not going to function.
Therefore you've got more heat emitting from that city.
On the other hand, if you do have soil moisture, you have
moisture in the soil, the temperature is controlled by
that latent heat.
So now, you don't have very much heat emitting from the surface.
So the flight, the airplane, the flight will be extremely smooth.
So that is continental versus marine.
We're looking at two environments, one, the
continentality effect, where you have a city that's in the middle
of a continent, or you have a city environment where there's
not much moisture stored at the surface.
And then you have the coastal regions, or coastal cities, and
you also have the urban or the rural regions where there's a
lot of moisture around to control that temperature.
Another control on temperature, the fourth control on
temperature is ocean currents.
Ocean currents help to moderate temperatures to the extreme
north and at the equator.
So for example, we have, if we consider here is the equator,
here is the polar region, the tropics are here, we'll say that
this is the USA and then over on this side we have Europe.
Now this is a very bare, basic, simple diagram.
We have a warm current that moves from the tropics close to
the eastern seaboard of the United States
and moves to the north.
This current is called the Gulfstream.
It takes warm water from the tropics and moves in this
current to the north, to moderate
temperatures in the polar region.
Therefore, you do not get a very cold, cold,
cold, environment in the polar regions.
It's still cold, but not as cold.
On the other hand, so the tropics do not get too hot, we
have a cold current that moves from the north to the south.
So on the eastern side of the basin, the oceanic basin, we
have cold currents that move from the north to the south to
help bring down those tropical temperatures.
So now we've got this moderation, warm, cold, warm,
cold in the northern hemisphere.
The same situation occurs in the southern hemisphere, so we're
moderating temperatures.
If this were to shut off, then what would happen, the tropics
get very warm and the polar regions get very cold, and we
see more ice form in the polar regions.
And this, this phenomenon is what has happened in the past
with climate change 5,000 years ago, and 15,000 years ago, to
18,000 years ago, and is a possibility we could see in the
future with continued climate change,
but we'll cover that at another time.
The final, the final control on temperature is cloud cover.
Cloud cover controls temperature at the surface.
So if you have, you have a clear day, contrary to what you might
think, if you have a clear day, you have insolation, you have
heat that escapes, clear day, it has to be extremely clear.
The relative temperature, without any clouds, is going to
be cool, because the heat is escaping in the atmosphere.
If you bring in the clouds, you also, you also have cool
conditions, no sun has been seen all day so there is no absorbing
at the surface so you get a cool day, because no insolation has
reached the surface of the earth to be
absorbed to increase that heat.
Now, if we consider changing this a little bit to make it
warmer, what we get is this, we get insolation, there's
absorption going on in the a.m..
Then in the afternoon, we get clouds moving in, we get clouds
moving in but what happens is, that radiation is being stored
at the surface it is emitting back and forth between the cloud
and the ground, so the cloud is acting like a blanket.
During the morning, you have accumulation of radiation at the
surface, it is emitting heat.
It continues to absorb solar radiation, but then the clouds
move in, in the afternoon, then you increase that temperature
because now the clouds are acting as a blanket.
So those are the basics of the five controls on temperature.
To recap, we had first, the latitude control on temperature
which is the cooling of temperatures to
the poles from the tropics.
We have altitude, where the lower elevations will have
greater temperature, more heat than higher elevations, even
though you might be closer to the sun.
Then you have continentality, continental versus marine.
This has everything to do with the bodies of water, where your
location is in regards to bodies of water, or no bodies of water.
Then we had the ocean currents, where you moderate the
temperature from tropics to the poles and vice versa.
You have transfer of heat, and transfer of cold temperatures
via the ocean currents, from the poles to the
tropics and vice versa.
And then finally we had cloud cover, where the clouds come on
in acting like a blanket, keeping things warm at the
surface, or no cloud cover which allows radiation
to escape into space.
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