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Air Masses & Weather

Air Masses & Weather. September 13, 2007. More Adiabatic Processes. Air masses are one of the following…. Unstable – describes an air mass that will just keep rising because its warmer than the surrounding air Occurs when the ELR is higher than the MAR and DAR Cloudy

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Air Masses & Weather

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  1. Air Masses & Weather September 13, 2007

  2. More Adiabatic Processes • Air masses are one of the following…. • Unstable – describes an air mass that will just keep rising because its warmer than the surrounding air • Occurs when the ELR is higher than the MAR and DAR • Cloudy • Stable – describes an air mass that will resist rising because it is cooler or the same temperature as the surrounding air • Occurs when the ELR is lower than the MAR and DAR • Clear weather

  3. Conditionally unstable – describes an air mass that is stable unless it is forced to begin cooling at the MAR • Occurs when the ELR is between the DAR and the MAR • Very common over mountain ranges where air is forced to rise

  4. Example • An unsaturated air parcel at the ground is 10ºC, the ELR is 8ºC/1000m, and the dewpt temperature is 2ºC. The air parcel is going over a mountain that is 2000m tall. What happens to the air parcel? • 10ºC/1000m * x = 8ºC • X = 800m, height of dewpt • What is the temperature of the air outside of the air parcel? • ELR = 8ºC/1000m

  5. 8ºC/1000m * 800m = 6.4ºC • 10ºC – 6.4ºC = 3.6ºC, temp of surrounding air at 800m • Temperature inside the air parcel at 800m is 2ºC. What will happen to the air parcel?

  6. Example • What happens on the leeward side of a mountain? • As an air mass moves down the leeward (dry) side of the mountain, it warms by the DAR (10ºC/1000m). Outside air temp: 20ºC 12ºC 1000m 22ºC

  7. Cloud Formation • Processes involved in cloud formation: • Condensation involves… • Adiabatic cooling • Dewpt temperature is reached • 100% relative humidity • Moisture droplet – clouds or fog • Cloud – condensation nuclei – involves particles in the atmosphere

  8. Air Masses • Air masses are distinctive bodies of air that reflect the characteristics of its source region • Categorized based on moisture content and temperature • Moisture categories: m = maritime (wet) and c = continental (dry) • Temperature categories: A (Arctic; coldest), P (polar; cold), T (Tropical; warm), and E (Equatorial; hot)

  9. Air Mass Modification • As air masses move away from their source region, they can take on characteristics more like the region they are moving over • An mT air mass traveling to Chicago would cool as it moves from the Gulf Coast • A cP air mass traveling to Texas would warm as it moves from Canada • Lake-Effect Snow

  10. Fronts • A front is the contact between 2 air masses of differing characteristics

  11. Cold Front

  12. Cold Front Weather conditions associated with a cold front.

  13. Warm Front

  14. Warm Front Weather conditions associated with a warm front.

  15. Occluded Front

  16. Stationary Front • An almost motionless collision of air masses • Common in summer • Produces wide range of weather, depending on strength of air masses • Eventually dissipates, or becomes warm or cold front

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