3-2 Atmospheric Mechanics

  1. EXPLAIN the term pressure gradient
    • The rate of pressure change perpendicular to the isobars.
    • The isobar spacing dictates the size of the pressure gradient force (PGF).
  2. EXPLAIN the term pressure gradient force
    • The Initiating force for ALL winds
    • High Pressure: Air descends downward and outward 
    • Low Pressure: Air moves inward and up.

    • STRONG: isobars are close together
    • WEAK: isobars are far apart

    Image Upload 1
  3. EXPLAIN and identify gradient winds and Buys Ballot's Law with respect to the isobars around pressure systems in the Northern Hemisphere
    • Caused by combination of Coriolis Force and Pressure Gradient Force
    • Above 2000 AGL
    • Winds move Parallel to Isobars (perpendicular to PGF)
    • High Pressure: Clockwise
    • Low Pressure: Counter Clockwise

    Image Upload 2
  4. EXPLAIN and identify the surface wind direction with respect to the gradient winds in a pressure system in the Northern Hemisphere
    • Surface Friction reduces the effects of the Coriolis Force
    • Below 2000 AGL
    • Causes 'Angled" winds
    • Crossing Isobars
    • High Pressure: Clockwise and out
    • Low Pressure: Counter Clockwise and into

    Image Upload 3
  5. DESCRIBE the jet stream
    • Located just below tropopause, 30000MSL
    • A narrow band of strong winds; 100-150kts and up to 250kts
  6. DESCRIBE sea breezes
    • Daytime heating of the land.
    • Air rises over land, cools off, and descends over water.
    • Image Upload 4
  7. DESCRIBE land breezes
    • Created by land cooling off at night. 
    • Air flows over water, warms up, rises, then descends over land
    • Image Upload 5
  8. DESCRIBE mountain winds
    Cools off at night and then descends down to the valley floor
  9. DESCRIBE valley winds
    • Valley heated by the sun
    • Warm air is displaced and forced up the mountain
  10. DEFINE saturation
    • Saturation is the point at which air can hold no more water.
    • Higher temp, more water vapor can be held
  11. DEFINE dew point temperature
    Temperature at which saturation occurs
  12. DEFINE dew point depression
    • the difference in Dew Point and actual Temperature
    • aka Dew Point Spread
  13. DEFINE relative humidity
    • The percent of saturation in the air.
    • Dew Point Spread of 4° F or 90% RH = condensation into fog or clouds.
  14. DESCRIBE the relationship between air temperature and dew point temperature with respect to saturation
    • Dew point swill ALWAYS be lower than the temperature.
    • Dew point spread of 4° F or 90% RH = condensation into fog or clouds.
  15. DESCRIBE the relationship between air temperature and dew point temperature with respect to saturation
    • Dew point swill ALWAYS be lower than the temperature.
    • Dew point spread of 4° F or 90% RH = condensation into fog or clouds.
  16. DESCRIBE the three characteristics of precipitation
    • Showers: Sudden beginning and ending. Abruptly changing intensity. Associated with cumuliform clouds
    • Continuous: Steady. NOT showery. Intensity changes gradually. Associated with stratiform clouds
    • Intermittent: Stops and starts at least one during the hour. Shower or steady. Associated with either cloud type
  17. DESCRIBE the types of precipitation
    • Drizzle: freezing or liquid
    • Rain: freezing or liquid
    • Frozen: Hail, Ice Pellets, Snowmobile, or snow grains
  18. DESCRIBE the four principal cloud groups
    • Low Clouds: Surface to 6500AGL
    • Middle Clouds: 6500AGL to 20000AGL
    • High Clouds: above 20000AGL
    • Special Clouds: Extensive vertical development
  19. DESCRIBE the weather conditions associated with Low Clouds
    • Surface to 6500 AGL
    • Mainly composed of water droplets
    • Icing accumulates faster on low clouds because they are more dense
    • Can lead to terrain collision
    • Turbulence: none to moderate
  20. DESCRIBE the weather conditions associated with Middle Clouds
    • 6500 to 20000 AGL
    • Mainly composed of ice crystals and water droplets (ALTO)
    • Fog is often present, expect poor visibility
    • Frequently dark and Turbulent
    • Icing: common
  21. DESCRIBE the weather conditions associated with High Clouds
    • Clouds above 20000 AGL
    • Mainly composed of ice crystals (CIRRO)
    • No Precipitation; no icing hazard
    • Moderate turbulence with severe or extreme turbulence in anvil thunderstorms.
  22. DESCRIBE the weather conditions associated with Special Clouds
    • Have extensive vertical development with high risk of Icing.
    • Severe to extreme Turbulence, Hail, Icing, Lightning, and others.
  23. DESCRIBE the types of atmospheric stability
    • Stable: Tendency to return to equilibrium
    • Neutral Stable: Equilibrium encountered at any displacement
    • Unstable: Tendency to move away from equilibrium
  24. DESCRIBE the four methods of lifting
    • F - Frontal: Cold fronts lift air preceding it
    • O - Orographic: Wind against a mountain side pushes the air up
    • C - Convergence: Forces air up in between air masses
    • T - Thermal: When cool air is over a warm surface, from solar heating
  25. DESCRIBE the flight conditions associated with a stable atmosphere
    Image Upload 6
  26. DESCRIBE the flight conditions associated with a unstable atmosphere
    Image Upload 7
Author
keggeler
ID
347692
Card Set
3-2 Atmospheric Mechanics
Description
API Weather 2017 Edition
Updated