Download Lecture 1 Wed. Oct 4 2006

What is meteorology??
(and why should you care?)
meteorology—The study of the
physics, chemistry, and dynamics of the
earth's atmosphere.
The American Meteorological Society defines a
meteorologist as a person with specialized education
"who uses scientific principles to explain,
understand, observe, or forecast the earth's
atmospheric phenomena and/or how the
atmosphere affects the earth and life on the
planet."
What do we mean by “severe and
unusual” weather extremes?
Severe weather not only includes things like heavy thunderstorms,
lightning, hail, flash floods, and tornadoes. . .
. . . but all
kinds of
hazardous
weather
In addition to the day to day weather, some
meteorologists study longer-term events like El
Niño, the ozone hole, acid rain, and global warming
Some meteorologists study how dust from Africa can be deposited in
Florida, or how changes on the Sun affect our atmosphere. Meteorologists
study how destruction of rain forests or eruptions of volcanoes can change
the composition of our atmosphere.
Europe’s main threats: flooding and heat
Extreme weather events are very
costly. And have been increasing
recently.
The first thing we need to know is
what the atmosphere is made of
Percent composition of dry atmosphere, by volume
ppmv: parts per million by volume
Gas
Volume
Nitrogen (N2)
78.084%
Oxygen (O2)
20.946%
Argon (Ar)
0.9340%
Carbon dioxide (CO2)
365 ppmv
In other words, more than 98% of the
atmosphere is nitrogen and oxygen
**Water vapor, not displayed in this
dry atmosphere chart, can occupy
anywhere from 0 – 4 % volume,
making it the most variable
atmospheric constituent
Amount of carbon dioxide in the atmosphere
has changed over time
• CO2 acts as a
“greenhouse” gas
– As heat rises from earth
surface, CO2 molecule
absorbs it & prevents
from escaping to space
• Net result: global
warming
• Impt. caveat: global
warming is WAY more
complicated than simply
looking at chg of CO2
over time
– At Mauna Loa, CO2
increased in the last 40
yrs, coincident with avg.
sfc. temp of earth
increasing ~ 1°C
*
The relative composition varies from place to place on the
surface of the Earth. The reason for this variation is the
presence of aerosols and water vapor - both of which vary
widely in amount:
 Aerosols: either tiny liquid droplets, such as fog, or tiny
solid particles, such as ice crystals, smoke, sea salt
crystals, dust, and volcanic emissions, suspended in the
air.
Aerosols play very important roles in cloud formation –
more on that later!
Next we need to know a little about the
general structure of the atmosphere.
Start with pressure.
Consider a column of air 1 inch2 in
size extending from sea level to the
top of the atmosphere:
The weight (=mass X gravity) of the
column of air will be about 14.7 lbs
Hence, the pressure at sea level is
= force/area = 14.7 lbs/inch2
Sea-level pressure is also given in
other units:
•14.7 lbs/inch2
•1013.25 millibars
•1013.25 hPa (hecto Pascals)
•29.92 inches of Hg (mercury)
Atmospheric pressure
decreases exponentially
with height.
50% of earth’s air lies in
the lowest 6 kilometers
(3.7 miles)
Atmosphere officially
extends up over 100
miles
Pressure is basically the “weight” of the air above a location – so if you’re
location is sea level, you have the greatest atmospheric pressure.
Pressure decreases exponentially with height (more air molecules are
found in air at the surface than in the same volume of air aloft)
Short clip about meteorologists, weather men,
hurricanes, and climate change
Atmosphere divided
into different levels
Meteorologists
concern ourselves
with the
TROPOSPHERE
Why??
Definition:
TEMPERATURE
INVERSION – a layer
of the atmosphere
where the temperature
increases with height
Rule of thumb: the
word “pause” indicates
the top of a layer.
Ozone is concentrated
in the stratosphere
At the top of the
troposphere is the
tropopause, which
marks the
beginning of the
temp. inversion of
the stratosphere
Thus the
tropopause acts as
a good level for the
top of buoyant
clouds
Note that
thunderstorm
clouds are tallest in
the tropics
Interesting
electromagnetic property
of the atmosphere: at
night ionosphere has
different properties than
during the day.
Thus, short-wave radio
waves (the “AM”
frequency) can be
reflected and travel long
distances – from
America to Europe
We need to keep in mind a few simple rules:
1.Warm air is less dense (“lighter”) than
cold air
2.Humid air is less dense than dry air
3.Less dense air can be forced up over
denser air
4.As air is forced upward, it cools and can
form clouds and precipitation (if there is
enough water vapor)
5.The type of precipitation that falls will
depend on the temperature of the air
and the ground
In addition to forecasting the daily weather, some
meteorologists study severe weather, and try to
predict where it will occur
Some meteorologists also work to be able to
better predict what our planet will be like in
the future by studying the past
OR
In short, meteorologists study the Earth system in an effort to
help us better understand our planet, for both the short and
long time-scales.
A few definitions we need to know:
Temperature: measure of hotness or coolness of the air.
Specifically a measure of the kinetic energy of an air
molecule
Pressure: the force of air above an area (remember,
mass x gravity)
Humidity: measure of amount of water vapor in the air