Meteorology – the study of weather
Weather…Part 1
Here are some variables that are a part of predicting the weather:
1. Air Temperature – depends on AOI, DOI, and IOI
(thermometer)
2. Air Pressure – the force exerted by the air overhead
(barometer)
3. Humidity – the amount of moisture in the air (hygrometer)
4. Wind Speed – (anemometer)
5. Wind Direction – (wind vane or weather vane)
6. Atmospheric Transparency- how clear the air is (ceiling)
7. Visibility – how far ahead you can see (in miles)
8. Wind Chill – how cold it feels (combo of temp. and wind)
9. Dew Point Temperature – the temp. air needs to cool to, in
order for condensation to happen (cloud forms)
All of these variables interact in the troposphere.
Mrs. Degl
1
People cannot accurately predict weather after 36 hours, b/c there are
too many weather variables working and changing at the same time.
The atmosphere gains energy in four ways:
1. Direct absorption of Insolation from the Sun- Only 19% of the
atmosphere’s heat comes from direct absorption.
2. Change of Phase reactions- Condensation and Sublimation
release energy to the atmosphere.
3. Terrestrial Radiation – the Earth releases heat (Infrared) as it
cools off at night.
4. The Greenhouse Effect – Carbon Dioxide and Water Vapor in our
atmosphere trap heat that is trying to escape into space.
All of the energy that is gained by the atmosphere is distributed
throughout the rest of the atmosphere by Convection Cells or
Convection Currents.
Mrs. Degl
2
Adiabatic Temperature Change – a change in
temperature of the air due to it expanding and contracting, not
being cooled or heated.
As air rises, it expands (spreads out), it’s volume
increases, and it’s temperature decreases after a while
of being away from the warmer surface.
As air sinks (falls), it contracts (compresses), it’s
volume decreases, and it’s temperature increases after a
while of being back on the surface of Earth where it is
warmer.
Memorize this!!!!!!!!
Mrs. Degl
3
Mrs. Degl
4
Air (Barometric)Pressure
The force exerted by the column of air overhead
Air pressure is influenced by:
1. Air temperature
2. Elevation above sea level
3. How much moisture is in the air.
1. As air temperature increases, air density decreases, so
air pressure also decreases. Hot air has a lower air
pressure.
As air temperature decreases, air density increases, so
air pressure also increases. Cold air has a higher air
pressure.
Mrs. Degl
5
2. As elevation increases (you get higher above sea level), air
pressure decreases, because there is less air over your head.
As elevation decreases (you get closer to sea level) air pressure
increases, because there is more air over your head.
3. Dry air is made of mostly Nitrogen. As air becomes
moister, Water Vapor replaces the Nitrogen. Water vapor
is less dense than Nitrogen. So, moist air has a lower air
pressure than dry air. Moist air is better and easier to
breath.
Mrs. Degl
6
We need to learn how to code and un-code air pressure values in order
to use and create weather maps.
Meteorologists do not put the real air pressure values on the weather
maps because the numbers are too long and take up too much
space on the map. They use a abbreviation system.
How to read the air pressure numbers on a map:
1. If the air pressure (in millibars) is below 500, put a 10 in
front of the number and a decimal between the last two
digits. This number is the real air pressure.
2. If the air pressure number is above 500, put a 9 in front of
it and a decimal between the last two digits.
How to put air pressure numbers onto a weather map:
1. Remove the 9 or 10 and the decimal in front of the the air
pressure number.
2. Place that number of the weather map in the correct spot.
Mrs. Degl
7
Wind – the horizontal (parallel) movement of air.
Facts about wind:
1. Winds are caused by differences in air pressure between two
locations. This difference in air pressure is caused by the differences
in temperature between two locations. So, in other words, winds are
caused by the unequal heating of the Earth. The larger the difference
in pressure, the stronger the wind.
2. Winds blow from areas of High Pressure to Low Pressure.
3. Winds blow from areas of Divergence to Convergence.
4. Winds are named after the direction that they are blowing from, not
where they are blowing to.
5. Surface ocean currents (not tides) are caused by wind direction.
1. Wind direction is also influenced by the Coriolis Effect (Rotation).
Winds curve to their right in the Northern Hemisphere, and to their
left in the Southern Hemisphere.
Mrs. Degl
8
Landbreezes and Seabreezes
During the day, the land heats up faster
than the water. The air over the land has a
lower density than the air over the water.
Because of this, the air over the land rises.
There is now an empty spot over the land,
so the air over the water fills it in. That is
why the breeze always comes off of the
water during the day. This is a seabreeze.
At night, the land also cools off quicker
than the water. This causes the water to
have a higher temperature than the land.
So, the air over the water now has a lower
density and it rises. Now the air over the
land must fill the empty spot. This is why
the breeze blows from the land to the
water at night (it comes from behind). This
is a landbreeze.
Mrs. Degl
9
Wind and Pressure Belts
Areas of Convergence – where the winds collide (0°, 60°N and 60 °S).
These latitudes are very wet and have a lower air pressure.
Areas of Divergence – where the winds blow away from each other.
(30°N, 30°S, 90°N, 90°S) These latitudes are dry (deserts of the world)
and have a much higher air pressure.
Mrs. Degl
10
Prevailing Winds – zones on the Earth’s surface where winds tend to
blow in the same direction over long periods of time. The prevailing
winds in NYS are called the southwesterlies (they blow from the SW).
See page 14 ESRT’s.
Jet Streams – a narrow zone of very strong winds in the upper
atmosphere (troposphere).
The Jet Streams steer weather systems across the world.
The Jet Stream in the USA steers weather from West to East.
The Jet Stream tends to migrate north in the summer and south in the
winter.
Mrs. Degl
11