Weather Chp. 27

I.  Atmospheric Moisture

  1. Phase changes of water are accompanied by a change in thermal energy of water
  2. Humidity- A measure of the amount of water vapor in the air
  3. 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.
  4. Water vapor in air

Possible water vapor at that temp

  1. Ex. 50% relative humidity - means the water content in the air is half the amount it could be.
  2. Warm air can hold more water than cold air
  3. As air rises it expands because of lower pressure
  4. Expanding air cools
  5. As air cools it slows down and begins to condense (water is polar)- occurs at the dew point
  6. As the water droplets grow they fall as rain, sleet, hail or snow -precipitation

II.  Air Behavior

  1. 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)

  1. Convectional lifting-warming air rises from “hot spots” followed by sinking cooler air
  2. Visualize a lava lamp
  3. Orographic lifting-air that is pushed up by a land mass
  4. Warm dry air sinks on opposite side creating a rain shadow
  5. Frontal lifting-(Figs. 27-11 and 27-12)
  6. Front- the contact zone between two air masses
  7. Differences in temp., moisture and pressure cause movement of air masses
  8. Cold front-cold into warm air mass
  9. Warm front-warm into cold

IV.  The Atmosphere

a.  Atmospheric Pressure

  1. Pressure exerted by air molecules because they have weight
  2. Decreases with increasing elevation
  3. Composed of primarily Nitrogen and Oxygen
  4. 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

V.  Violent Weather

  1. Thunderstorms-
  2. Humid air rises cools and condenses
  3. Lightning-
  4. falling water droplets bump into and rub against one another
  5. cloud becomes electrically charged and release as lightning
  6. Thunder- lightning heats air up and it expands so fast it breaks the sound barrier
  7. Fun Facts
  8. ~1800 thunderstorms in progress in earth’s atmos.
  9. lightning strikes ~100 times every sec.
  10. Claims more than 200 people/ yr.
  11. Tornadoes-funnel cloud that has touched the ground
  12. Hurricanes-
  13. Winds up to 300 km/hr.
  14. Caused by a long supply of warm, moist air

VI.  Clouds (table 27.1)

  1. High Clouds- (cirro)
  2. Cirrus-wispy
  3. Cirrostratus-sheet like
  4. Cirrocumulus-fish scales
  5. Middle Clouds- (alto)
  6. Altostratus-prevent shadows
  7. Altocumulus-long puffy strips or blotches
  8. Low clouds
  9. Stratus- gray and cover entire sky
  10. Statocumulus-wide gray, puffy clouds
  11. Nimbostratus- Cover sky, wet looking, “fog”
  12. Vertical Clouds
  13. Cumulus- pillowy
  14. Cumulonimbus- anvil shaped, tall clouds, produce tornadoes