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Pressure
1. Barometric Pressure
  1. mb, in. of mercury
  2. barometer
  3. weight of the overlaying atmosphere pushing down on a unit of area
  4. isobars
    1. form circular patterns showing large masses of air
2. Factors that Affect Pressure
  1. > Temp = farther apart molecules = < pressure
  2. >altitude = air < dense, = < pressure
  3. MOISTURE: Humidity > = > H20, lighter than O2/N2, = < pressure
    1. water vapor enters atmosphere via evaporation, sublimation, and transpiration
      1. Factors that Affect Rate of Evaporation
        Temp >, R.O.E. >
        Humidity >, R.O.E. <
        Wind >, R.O.E. >
        Sur. Area >, R.O.E >
    2. Saturation
      1. rate of evaporation = rate of condensation
      2. when air holds as much water vapor as possible at given temp
      3. Dew Point
        Temp the air must be cooled to to reach saturation
        Affected by amount of WV in air, NOT R.H.
        sling psychrometer
        When air temp + dew point are =, air is saturated, and condensation occurs
        decreases w/altitude
        As water vapor increases, dew point temp increases
    3. Humidity
      1. As temp >, the amount of water vapor that can be hold >.
      2. Absolute Humidity: Amount (mass) of water vapor in air
      3. Relative Humdity (RH): Amount of W.V. in air compared to how much can be held.
      4. Sling Psychrometer
        dry bulb = air temp
        Wet bulb depends on R.O.E., thus depends on dryness of air
3. Pressure systems
  1. High pressure
    1. anticyclone
    2. winds blow clockwise and away from center
    3. sinking air
    4. cool, dry weather
  2. Low Pressure
    1. cyclone
    2. winds blow counterclockwise and towards center
    3. rising air
  3. As pressure gradient >, wind speed >
Clouds
1. In order to form:
  1. moisture in air
  2. cooling temperature (due to rising air)
  3. condensation nuclei (aerosols, dust particles)
2. Formation:
  1. I. warm air rises
  2. II. Rising air expands
  3. III. Expanding air cools to the dew point temp
  4. IV. At dew point temp, condensation occurs and clouds form
  5. Adiabatic Cooling
    1. Cooling of air due to expansion, rising air expands and cools
    2. Forms clouds in low pressure
  6. Adiabatic Warming
    1. Warming of air due to compression, sinking of air compresses and warms
    2. No clouds form in high pressure systems
Air Masses
1. Large body of air in troposphere with similar characteristics of temp, moisture, and press
  1. Tropical: form @ tropics, high temps
  2. Polar: form @ high latitudes, low temps
  3. Arctic = VERY cold
  4. Continental: form @ land, dry
  5. Maritime: form @ water, wet
2. Source Region = where air mass forms
  1. take on characteristics of surfaces over which they form
Fronts
1. Cold
  1. cold air mass moves into region of warm air
    1. Cold air = dense, stays near surface
      1. forces less dense warm air to rise above it
        Thus, clouds form at leading edge
    2. Precip occurs along frontal boundary at surface
      1. narrow band of heavy rain/thunderstorms
2. Warm
  1. warm air mass moves into region of cold air
    1. warm, less dense air is forced to rise over the top
    2. Precip occurs before frontal boundary at surface
    3. Wide band of steady, all day shower
3. Stationary
  1. 2 different air masses not moving relative to one another
    1. steady, heavy rain
    2. precip occurs in a wide band along the front at the surface
4. Occluded
  1. cold air mass moves into and takes over a region of warm air
    1. steady, all day rains followed by heavy rain/thunderstorms
    2. precip occurs in a wide band before and along the front
5. Always associated with low pressure systems
  1. counterclockwise circulation of air in L press draw warm, moist air up from lower latitude and colder, dry air down from high latitudes
Rain
1. occurs when air rises, expands, cools adiabatically to dew point temp, condenses to form clouds, ff droplets get heavy enough to fall
2. Areas of Rain
  1. Windward Wide of Mountain/Orographic Effect
    1. Windward side is cool, wet
    2. air rises as it is forced over mountain
    3. Leeward side is cool and dry
      1. Rain shadow - very dry region on leeward side of mountain due to sinking air
  2. Equatorial Regions
    1. Warm air rises due to convection
    2. Recieve most direct insolation, so air is heated and rises
  3. Low Pressure Systems
    1. Surface air converges and rises at center of L. press systems
  4. Fronts
    1. Warm, less dense air rises over colder, more dense air
  5. Areas with little rain
    1. where air is sinking, compresses, warms (adiabatically)
Storms
1. Thunderstorms
  1. Form from uplifting warm air associated with cold front
  2. located in inland regions
  3. produce heavy rains, hail, winds, thunder/lighting
2. Tornadoes
  1. rapidly rotating low press. funnel associated with strong thunderstorms and cold fronts in spring
  2. Very narrow: 100 ft - 1 mile in dm
  3. Last for few minutes to an hour
3. Hurricanes
  1. Form as low pressure centers over warm tropical waters in late summer/early fall
  2. gain energy from condensation of moisture evaporated over warm ocean water
  3. Warm rising air produces a very strong low pressure system
  4. Lose strength as they move over land
  5. Flooding along coast - storm surge-causes most damage
  6. Minimum winds = 74 mph
4. Lake Effect Snow
  1. prevailing winds move across the rel. warm Great Lakes, pick up moisture, which is uplifted over Tug Hill, where it snows dues to orographic effect
5. Storm Tracks
  1. Prevailing Westerlies - winds over US
    1. blow W -> East
  2. Tropical storms that affect US develop West of Africa
    1. trade winds carry them to US South east

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	Created by Nadia Taeckens almost 7 years ago