AOSC 200

Lesson 2

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

MILLIONETH 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

Fig. 1-11, p. 12

Smoke from Forest Fires along the coast of California.

Fig. 1.11

Smoke from Forest Fire in New Mexico

Toricello

• Filled a glass tube 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.CONSTANT• 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

2. Stratosphere- layer above the tropopause, little mixing occurs in the stratosphere, unlike the troposphere, where “turbulent mixing” is common

3. Mesosphere- defined as the region where temperature again decreases with height.

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).

Tropopause

Stratopause

Mesopause

When the atmosphere moves it tends to movealong 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 m (5000 ft)700 mb 3000 m (10,000 ft)500 mb 5500 m (18000)300 mb 9000 m (30,000)

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

Fig. 9.13

Warm Front

Fig. 9.15

Cold front

Fig. 1-17, p. 21

Weather Symbols

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.