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AOSC 200 SUMMER 2010
Everybody talks about the weather but
nobody does anything about it.
- Charles Dudley Warner
AOSC 200 Weather and Climate
Lecture Time and Location:
Monday through Friday- 9:00 am to 11.30 am CSS 2416
Discussion Time and Location
Monday through Friday - 1.00 pm to 3.00 pm, CSS 3426
Textbook: Meteorology: Understanding the Atmosphere,
by Ackerman and Knox
AOSC 200 Weather and Climate
•
Course website
www.atmos.umd.edu/~hudson/aosc200.d
•
Contains:
(1) Each lecture in Power-point format on web page.
Go to AOSC200 LECTURES
Syllabus and class schedule
(1) All class information will be posted on the website.
•
A weather forecasting primer can be found at
www.atmos.umd.edu/~hudson/forecastchecklist2010.htm
Grading
• The course will be graded on the basis of a mid-term
exams (25% of the final grade) , a final exam(30% of
the final grade), 7 lab projects (25% of the final grade),
and 4 quizzes (20% of the final grade).
Who am I?
• My PhD was in Physics. My research thesis was in
Spectroscopy. Each molecule or atom emits and absorbs
radiation in unique regions – like a finger print. One can
use this fact to identify the molecule or atom.
• Before joining UM in 1990, I worked for NASA
developing instruments to identify atmospheric
molecules from satellites.
• It was at NASA that I became an atmospheric physicist
• Research on the Ozone layer in the Stratosphere.
• Current research is on applying this ozone data to
climate studies.
http://www.youtube.com/watch?v=
YfcNRWefEEU
http://www.youtube.com/watch?v=
YfcNRWefEEU
The Blue Marble
http://www.youtube.com/watch?v=
KRdi5ElayK4
http://www.youtube.com/watch?v=
KRdi5ElayK4
Weather Satellite Image, July 7, 2005
Fig. 1-1, p. 2
Weather vs. Climate
Weather
Climate
Instantaneous description
of what the atmosphere
is doing at a particular
time and place
Description of what
weather is usually like in
a region (large or small).
Not just the average
weather, but a
description of what the
extremes are like too.
Different hemispheres –
different weather
Why?
Different ratios of land to
oceans.
Oceans tend to act like a
thermostat.
Mountains cause instabilities in
the air flow. Southern
hemisphere is calmer.
Fig. 1-2, p. 3
Mean Percentage of possible sunshine for November
Typical Weather Map
Typical Climatology Map
Surface Pressure Map Jan 25
850 Mb chart for Monday Jan 25
FRONTS
• You will often hear TV meteorologists refer to cold
and warm fronts when describing the weather.
• Fronts are regions where cold and warm air masses
meet.
• This is the region where most of the ‘weather’ is
generated.
• We identifiy four main classes of fronts, warm, cold,
stationary, occluded.
• Each front has an unique symbol on weather maps.
Fig. 1-15, p. 18
Warm Front
Fig. 9.13
Cold front
Fig. 9.15
Weather Symbols
Fig. 1-17, p. 21
Detailed weather symbols
(1) Direction of arrow into the circle gives the wind direction. Number of barbs
on the arrow gives the wind speed. Full barb = 10 miles per hour, half barb=5.
(2) Sign, middle left, gives the type of precipitation. In the top left symbol the
sign is fot thunder. In the bottom left it stands for steady rain.
(3) Shading in inner circle gives the cloud fraction.
(4) Top number on left is the temperature, bottom number the dew point
Weather symbols
• The numbers at top right of each symbol represent the
pressure in millibars (mb)
• The pressure seldom drops below 950 mb and seldom
gets above 1049 mb
• In the days of teletype the object was to shorten the
amount of information sent.
• So if I say the pressure was 98 then the receiver could
assume that I meant 998. And if I sent 14 then 1014
was assumed.
• To further confuse the issue it was decided to sent the
tenth of a mb. So now if I sent 998 I meant 999.8.
Similarly 117 means 1011.7.
Weather Forecasting
• A website has been prepared to guide you
through the process of making a simple
weather forecast.
• You can either go to Dr. Hudson’s web
page and then click on:
Forecast Checklist
• Or go to:
http://www.atmos.umd.edu/~hudson/forecas
tchechecklist-2010.htm
BREAK
Composition of the Earth’s Troposphere
H2
O2
CH4
N2
N2O
PM
CO
O3
←SO2, NO2,
CFC’s, etc
Ar
CO2
Inert gases
Table 1-1, p. 4
Atmospheric Composition
• MOLECULAR OXYGEN AND NITROGEN ARE
MAJOR COMPONENTS – 99%
• OF THE REMAINING 3% , 97% IS THE INERT
GAS ARGON
• OF THE REMAINING 7%, 93% IS CARBON
DIOXIDE
• ALL REMAINING GASES – ABOUT 2 PARTS IN
100,000 ARE KNOWN AS TRACE SPECIES
• THESE GASES CONTROL THE CHEMISTRY OF
THE TROPOSPHERE
Atmospheric Evolution
• Earth’s early atmosphere consisted of Hydrogen (H),
Helium (He), Methane (CH4) and Ammonia (NH3)
• As the earth cooled volcanic eruptions occurred emitting
water vapor (H2O), carbon dioxide (CO2) and molecular
nitrogen (N2).
• The molecular oxygen (O2) in the current atmosphere came
about as single celled algae developed in the oceans about
3 billion years ago.
• The oxygen is produced as a by-product of photosynthesis,
the making of sugars from water vapor and carbon dioxide.
• This oxygen produced ozone in the upper atmosphere
which filtered out harmful ultraviolet radiation from the
sun. This allowed plants and animals to develop on land.
Fig. 1-4, p. 7
Fig. 1-3, p. 6
Carbon Dioxide Cycle
•
•
•
•
•
•
•
•
•
•
SOURCES
VOLCANOES
PLANT/ANIMAL RESPIRATION
PLANT DECAY
BURNING OF FOSSIL FUELS
DEFORESTATION
SINKS
PLANT PHOTOSYNTHESIS
OCEANS
CARBONATES
Hydrologic Cycle
Fig. 1-5, p. 8
Hydrologic Cycle
• WATER IS EVERYWHERE ON EARTH
• IT IS IN THE OCEANS, GLACIERS, RIVERS,
LAKES, THE ATMOSPHERE, SOIL, AND IN
LIVING TISSUE
• ALL OT THESE ‘RESERVOIRS’ CONSTITUTE
THE HYDROSPHERE
• THE CONTINUOUS EXCHANGE OF WATER
AMONGST THE ‘RESERVOIRS’ IS KNOWN AS
THE HYDROLOGIC CYCLE
• THE HYDROLOGIC CYCLE IS POWERED BY
ENERGY FROM THE SUN
• EVAPORATION AND TRANSPIRATION
• PRECIPITATION
• RUN-OFF TO THE SEA
Other important Gases
• Methane - CH4
• Is produced whenever plant material decays below water, e.g.
in marshes and rice paddies.
• Is a greenhouse gas. Has a long lifetime in the Troposphere but
breaks down in the Stratosphere to form water.
• Cholofluorocarbons - scientific name for the Freons.
• Are greenhouse gases
• Have a long lifetime in the Troposphere but break down in the
Stratosphere to releases chlorine. Responsible for the Ozone
Hole.
• Emissions were banned as a result of the Montreal Protocol.
Fig. 1-7, p. 9
Fig. 1-8, p. 10
Fig. 1-9, p. 11
Aerosols
• PARTICLES SUSPENDED IN THE ATMOSPHERE
• DIAMETERS MEASURED IN MICRONS – ONE
MILLIONTH OF A METER.
• CAN MODIFY THE AMOUNT OF SOLAR ENERGY
THAT REACHES THE SURFACE.
• CAN ACT AS CONDENSATION NUCLEI FOR
CLOUD DROPLETS.
• PRIMARY SOURCES:
• SEA SALT SPRAY
• WIND EROSION
• VOLCANOES
• FIRES
• HUMAN ACTIVITY
Fig. 1-10, p. 11
Smoke from Forest
Fires along the coast
of California.
Fig. 1-11, p. 12
Smoke from
Forest Fire in
New Mexico
Fig. 1.11
Fig. 1-13, p. 15
Toricello
• Filled a glass tube with mercury that had been
sealed at one end
• He then inverted the tube in a bowl of mercury
• Found that the mercury did not flow out of the
tube but remained in the tube, and that the height
of the mercury column was constant each time he
tried the experiment.
• He reasoned that the air was keeping the mercury
in the column by pressing down on the bowl of
mercury.
Fig. 1.13
Fig. 1-13, p. 15
Fig. 1.12
Atmospheric Pressure
• PRESSURE AT A POINT IS THE WEIGHT OF AIR
ABOVE THAT POINT
• A COLUMN OF AIR AT THE SURFACE WEIGHS
SLIGHTLY MORE THAN 1 KILOGRAM PER
SQUARE CENTIMETER
• IN STILL AIR, TWO FACTORS DETERMINE THE
PRESSURE – TEMPERATURE AND DENSITY
• IDEAL GAS LAW
• PRESSURE =
DENSITY.TIMES.TEMPERATURE.TIMES.CONST
ANT
• PRESSURE CHANGES WITH ALTITUDE
Fig. 1-14, p. 17
1. Troposphere- literally means region where air “turns over”
-temperature usually decreases (on average ~6.5°C/km) with altitude
Tropopause
2. Stratosphere- layer above the tropopause, little mixing occurs in
the stratosphere, unlike the troposphere, where “turbulent mixing”
is common
Stratopause
3. Mesosphere- defined as the region where temperature again
decreases with height.
Mesopause
4. Thermosphere- region with very little of the atmosphere’s mass.
high energy radiation received by the thermosphere (high
temperatures experienced). A small density of molecules (not
much “heat” would be felt).
When the atmosphere moves it tends to move
along constant pressure lines (isobars) and not
along constant altitude lines.
In meteorology it is helpful to refer to altitude
as a certain pressure value rather than a height.
850 mb  1500
700 mb  3000
500 mb  5500
300 mb  9000
m
m
m
m
(5000 ft)
(10,000 ft)
(18000)
(30,000)