I.
II.
Weather Chp. 27
Atmospheric Moisture
a. Phase changes of water are accompanied by a change in thermal energy of water
b. Humidity- A measure of the amount of water vapor in the air
c. Relative Humidity- the ratio of the amount of water vapor currently in the air at a
given temperature to the largest amount of water vapor the air can contain at that
temp.
i.
Water vapor in air
Possible water vapor at that temp
ii. Ex. 50% relative humidity - means the water content in the air is half the
amount it could be.
iii. Warm air can hold more water than cold air
d. As air rises it expands because of lower pressure
e. Expanding air cools
f. As air cools it slows down and begins to condense (water is polar)- occurs at the
dew point
g. As the water droplets grow they fall as rain, sleet, hail or snow -precipitation
Air Behavior
a. Temperature changes in air is due only to pressure changes
b. Upper regions of air are warmer than lower regions leads to a temperature
inversion
Ex. Denver’s smog problem
Air rises as long as it is less dense than the air above it.
III.
Air Masses- (fig 27.8)
a. Convectional lifting-warming air rises from “hot spots” followed by sinking
cooler air
i. Visualize a lava lamp
b. Orographic lifting-air that is pushed up by a land mass
i. Warm dry air sinks on opposite side creating a rain shadow
c. Frontal lifting-(Figs. 27-11 and 27-12)
i. Front- the contact zone between two air masses
ii. Differences in temp., moisture and pressure cause movement of air masses
iii. Cold front-cold into warm air mass
iv. Warm front-warm into cold
IV.
The Atmosphere
a. Atmospheric Pressure
i. Pressure exerted by air molecules because they have weight
ii. Decreases with increasing elevation
iii. Composed of primarily Nitrogen and Oxygen
V.
VI.
b. Layers of the Atmosphere
i. Thermosphere
1. 90- 500 km
ii. Mesosphere
1. 50-90 km
iii. Stratosphere
1. 16-50 km
2. contains the ozone layer
3. 99% of atmosphere is below 35 km
iv. Troposphere
1. 16 km at the equator
2. 8 km at poles
3. commercial jets fly at the top of troposphere to avoid weather
4. 90% of atmosphere’s air mass
5. all water vapor and clouds
Violent Weather
a. Thunderstormsi. Humid air rises cools and condenses
ii. Lightning1. falling water droplets bump into and rub against one another
2. cloud becomes electrically charged and release as lightning
iii. Thunder- lightning heats air up and it expands so fast it breaks the sound
barrier
iv. Fun Facts
1. ~1800 thunderstorms in progress in earth’s atmos.
2. lightning strikes ~100 times every sec.
3. Claims more than 200 people/ yr.
b. Tornadoes-funnel cloud that has touched the ground
c. Hurricanesi. Winds up to 300 km/hr.
ii. Caused by a long supply of warm, moist air
Clouds (table 27.1)
a. High Clouds- (cirro)
i. Cirrus-wispy
ii. Cirrostratus-sheet like
iii. Cirrocumulus-fish scales
b. Middle Clouds- (alto)
i. Altostratus-prevent shadows
ii. Altocumulus-long puffy strips or blotches
c. Low clouds
i. Stratus- gray and cover entire sky
ii. Statocumulus-wide gray, puffy clouds
iii. Nimbostratus- Cover sky, wet looking, “fog”
d. Vertical Clouds
i. Cumulus- pillowy
ii. Cumulonimbus- anvil shaped, tall clouds, produce tornadoes