AIR MASS

DEFINITION:

AIR MASS: Is A Volume Of Air Defined By Its Temperature And Water Vapor Content. Air Masses Cover Many Hundreds Or Thousands Of Square Kilometers and sometimes as high as the top of the troposphere (about 10–18 km [6–11 miles] above the Earth’s surface), And Adapt To The Characteristics Of The Surface Below Them.

An air mass forms whenever the atmosphere remains in contact with a large, relatively uniform land or sea surface for a time sufficiently long to acquire the temperature and moisture properties of that surface.

Once An Air Mass Moves Away From Its Source Region, Underlying Vegetation And Water Bodies Can Quickly Modify Its Character.

CLASSIFICATION:

Air Mass Classification Involves Two Letters.

  1. The First Letter Describes Its Moisture Properties, Which They Are:
    • ‘C’ Used For Continental Air Masses (Dry).
    • ‘M’ For Maritime Air Masses (Moist).
  2. The Second Letter Describes The Thermal Characteristic Of Its Source Region, Which They Are:
    • ‘T’ For Tropical.
    • ‘P’ For Polar
    • ‘A’ For Arctic Or Antarctic
    • ‘M’ For Monsoon
    • ‘E’ For Equatorial
    • ‘S’ For Superior Air (An Adiabatically☀ Drying And Warming Air Formed By Significant Downward Motion In The Atmosphere).

☀: When A Gas Is Compressed Under Adiabatic Process, Its Pressure Increases And Its Temperature Rises Without The Gain Or Loss Of Any Heat. Conversely, When A Gas Expands Under Adiabatic Conditions, Its Pressure And Temperature Both Decrease Without The Gain Or Loss Of Heat.

For More Info About “ADIABATIC PROCESS”: Wikipedia

CHARACTERISTICS:

Arctic Air Masses:

  1. Developed Over Ice And Snow-covered Ground.
  2. Deeply Cold.
  3. Colder Than Polar Air Masses.
  4. Can Be Shallow In The Summer.
  5. Rapidly Modify As It Moves Equator-ward.

Polar Air Masses:

  1. Develop Over Higher Latitudes Over The Land Or Ocean.
  2. Very Stable.
  3. Generally Shallower Than Arctic Air.
  4. Polar Air Over The Ocean (Maritime) Loses Its Stability As It Gains Moisture Over Warmer Ocean Waters.

Tropical And Equatorial Air Masses:

  1. They Are Hot As They Develop Over Lower Latitudes.
  2. Those That Develop Over Land (Continental) Are Drier And Hotter Than Those That Develop Over Oceans, And Travel Pole-ward On The Western Periphery Of The Subtropical Ridge.