Meteorology - the study of the atmosphere (including
The atmosphere is the layer of air that
surrounds the Earth. It is made up of about:
0.03% Carbon Dioxide
<1 to 3% Water Vapor
(varies by region and season)
Pressure is the weight of the atmosphere pushing down on you.
This is about 1,000 kg (about 2,200 pounds) of air! Air pressure is measured
using a barometer. Air pressure drops as you rise higher into
The atmosphere is divided into several layers:
The troposphere is closest to the ground. It extends
upwards for about 10 km. The air is thickest in this level and
of our weather takes place here. For each kilometer
you climb into
the troposphere, the temperature will drop 6.5
stratosphere reaches from about 10 to 50 km above
ground. The temperature in this layer rises to about 0
This is due to the ozone layer, which absorbs
ultraviolet light (UV) from the sun and turns it into heat.
mesosphere reaches from about 50 to 85 km above the
ground. This is the coldest layer, with temperatures dropping
as -90 degrees C.
4. The thermosphere reaches from about
85 to 600 km above
the ground. The temperature rises again in this
as high as 2,000 degrees C.
ionosphere is inside the thermosphere. It reaches
about 80 to about 400 km above the ground. This layer
contains electrically-charged particles (ions), which are
formed when this layer absorbs solar energy. The ionosphere
Energy in the
Earth receives about 2/1,000,000,000 of the sun's total
energy. Of that, about half is either absorbed by the atmosphere or reflected
back into space.
The type of energy that we get from the sun is called
radiant energy. Radiant energy is energy that travels through
space in waves. This includes gamma rays, x-rays, ultraviolet (UV) light,
visible light, infrared light, microwaves, and radio waves.
Law of Conservation of Energy states that energy cannot be
created or destroyed, but it can change form. This means that light that is
absorbed can be converted into heat.
Some of the energy that the Earth
receives from the sun is trapped in our atmosphere by gasses, such as carbon
ioxide and water vapor. This trapped energy is converted into heat and helps to
warm the Earth. This process is called the Greenhouse
Convection is the movement of fluids
(gas or liquid) due to changes in temperature. In other words, warm air rises
and cool air sinks. A complete cycle of air moving due to differences in
temperature is called a convection cell. Convection cells can
cause land and sea breezes, mountain and valley
breezes, and monsoons. (These were
discussed, with diagrams, in class.)
Convection drives the three
major wind belts: the trade winds (closest to the equator), the westerlies (in
the middle latitudes), and the polar easterlies (near the poles).
Humidity is moisture in the air. It
can be described in one of two ways:
Absolute Humidity is
a measure of how much water is in the
air. This is expressed in terms
of grams per cubic meter.
Relative Humidity is a measure
of how much water is in the air
compared to how much water the
air can hold. This is
expressed as a percent. For example, air that
humidity cannot take in any more water. This means that
air is saturated.
Rule of Thumb: The warmer the air is,
the more moisture it can hold.
When the temperature drops to the point
where the air cannot hold the humidity that it had, this extra water comes out
of the air as condensation (water turning from a gas into a
liquid). This water that appears out of the air forms dew - or
frost, if the temperature is below freezing. The dew
point is the temperature at which the air is saturated, and dew can
classified by their shapes:
- Cumulus clouds are puffy and
shaped like cottonballs.
- Stratus clouds form flat
- Cirrus clouds are wispy and feathery.
general rule, clouds get more wispy as you go higher into the atmosphere. Below
2 km, you find cumulus and stratus clouds. Sometimes you'll see clouds that
seem both puffy and layered. These are called stratocumulus.
Clouds between 2 and 7 km high add "alto-" to their name; thus,
altocumulus and altostratus. Cirrus clouds
form above 7km. Cumulus and stratus clouds at this height add
"cirro-" to their name (cirrocumulus and
Rainclouds can be either
cumulonimbus (puffy) or nimbostratus
(layered). Cumulonimbus clouds are sometimes called thunderheads. These tend
to bring heavy rains for shorter periods of time. Nimbostratus tend to bring
lighter rains over a longer period of time.
is basically water falling form the sky. There are four basic
- Cloud droplets grow as moisture
is added until they are too
heavy to stay in the cloud. They then
fall to the ground as
If it's cold enough, the cloud droplets freeze - which forms
crystals. As moisture is added, the crystals grow until
heavy enough to fall as snow.
3. Sleet(a.k.a.: freezing rain)
- Sleet begins as
rain or snow.
- As rain falls, it may pass through a layer of cold air
freeze into sleet.
- As snow falls, it may pass through
a layer of warm air and
melt, then pass back into cold air and
re-freeze into sleet.
- Hail begins as
- As it falls, wind blows it back up into the clouds, where
picks up more moisture. This causes the hail to get
- This process repeats until the hail is too heavy for the wind
carry it back up into the clouds.
- Depending on how
strong the wind is, hail can grow as large
as grapefruit or
Air Masses &
An air mass is a large body of air that has
taken on the temperature and humidity of a part of the Earth's surface. Air
masses can be warm or cold, dry or moist.
Rule of thumb: Air
masses don't mix - but they do push against each other.
boundary between two air masses is called a front. There are
basically three types of fronts:
1. Cold Front
Cold fronts occur where cold air moves in and replaces
Because the cold air is denser, it can push up
the warm air the way
that a snowplow pushes up snow in
front of it. The rising warm air
cools off and forms
cumulonimbus (thunderhead) clouds. A
squall line is a
string of thunderstorms along a
2. Warm Front
- Warm fronts occur
when warm air moves in and replaces
cold air. Because the cold air
is denser, the warm air will
tend to ride up over it. As it rides
higher, clouds form:
nimbostratus at the low end, followed
altostratus, and finally
cirrus clouds at the higher, leading end.
- The air masses on either side of this front are not
Isotherm - A line on a map that passes through
locations that have the same temperature. Isotherms are useful in locating air
climate is the average weather in an area over a long period of
time (decades or centuries). There are three main climate zones in the world:
tropical (near the equator), polar (near the poles), and
temperate (between tropical and polar).
The Jet Stream
The Jet Stream
is a band of winds that form along the Polar Front (the
boundary between cold polar air and warm tropical air). The Jet Stream winds
move at speeds of about 120-240 km per hour, and occur at an altitude of about
10-15 km above the ground.
A cyclone is a huge mass of spinning
air. In the Northern Hemisphere, cycles generally move in a couterclockwise
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