Ground School: Meteorology 5.08 Air Masses References: - FTGU, pages 139 and 140 -Air Command Weather Manual, Chapters 6 and 19 40 Minutes

Ground School 5.08 Meteorology – Review 1. What creates wind? The horizontal pressure differences. 2. What do isobars on a map represent? Lines of equal pressure. 3. The ______________ the isobars are on a map, the stronger the winds. Closer together 4. As you go up in altitude, what happens to the winds? Veer and increase 5. When does a land breeze occur? During the night

Ground School 5.08 Meteorology – Air Masses MTPs: Air Masses – Definition and Characteristics Formation Classifications Modification Geographic factors Seasonal Effects

Ground School 5.08 Meteorology – Air Masses Definition: A large section of the troposphere with uniform properties of temperature and moisture May be several thousand miles across Cold Air Masses Warm Air Mass Instability Stability Turbulence Smooth air Good visibility Poor visibility Cumuliform clouds Stratiform Clouds and Fog Shower type precipitation Drizzle type Precipitation Hail, Thunderstorms may occur

Ground School 5.08 Meteorology – Air mass formation Air masses develop uniform properties of temperature and moisture Source Regions: Formed over the ice and snow surfaces of the Arctic would be cold and dry Formed over the South Pacific would be warm and moist Air masses develop uniform properties of temperature and moisture when a large part of the troposphere comes under the influence of a large part of the earth’s surface for a long period of time These areas are called Source Regions An air mass formed over the ice and snow surfaces of the Arctic would be cold and dry An air mass formed over the South Pacific would be warm and moist.

Ground School 5.08 Meteorology – Air mass formation Three main sources over North America Arctic (A) Cold Extends from the North Pole south to the permafrost line Polar (P) Cool Extends south from the permafrost line to where the temperature is 10°C Tropical (T) Very warm Lies below Latitude 30°N.

Ground School 5.08 Meteorology – Air mass formation Two Sub-Categories: Continental (c) - Dry Maritime (m) - Moist

Ground School 5.08 Meteorology – Air mass classifications Continental Arctic (cA): Forms over poles (usually in winter) From polar regions across prairies, into east Low moisture, Very cold, Very stable Very low tropopause. Pacific Ocean Atlantic Gulf of Mexico

Ground School 5.08 Meteorology – Air mass classifications Maritime Arctic (mA): Forms over Alaska or Siberia Spends short time over North Pacific Ocean Moist, Cold, Unstable in low levels Low tropopause. Pacific Ocean Atlantic Gulf of Mexico

Ground School 5.08 Meteorology – Air mass classifications Maritime Polar (mP): Forms over Arctic, Alaska and Northern Russia Spends longer time over Pacific Ocean than mA Moist, Warmer than mA, More stable than mA Medium height tropopause. Pacific Ocean Atlantic Gulf of Mexico

Ground School 5.08 Meteorology – Air mass classifications Maritime Tropical (mT): Forms over oceans and bodies of water in the Tropics Rarely appears north of Great Lakes Causes fog that effects Atlantic provinces Moist, Very warm, Unstable High tropopause. Pacific Ocean Atlantic Arctic

Ground School 5.08 Meteorology – Air mass modification As air masses move from their source region, they become modified Degree of modification depends on three factors: Speed at which the air mass moves Make up of the surface (i.e. land or water) 3. Temperature difference between air mass and new region’s surface temperature.

Ground School 5.08 Meteorology – Air mass modification

Ground School 5.08 Meteorology – Geographic factors The temperature of the oceans is a major factor North Pacific Current supplies warm water along the West Coast of Canada This warm water current maintains the Gulf of Alaska ice free through the winter

Ground School 5.08 Meteorology – Geographic factors Mountains On land the Rocky Mountains and the Coastal Range barrier extends unbroken from Alaska to Mexico with peaks extending up to 10,000 - 15,000 feet

Ground School 5.08 Meteorology – Geographic factors Lakes Northern Canada is covered with lakes that are open and provide moisture to the air in summer, but are frozen in winter.

Ground School 5.08 Meteorology – Seasonal effects

Ground School 5.08 Meteorology – Confirmation What are the characteristics of a Cold Air Mass? Instability, Turbulence, Good visibility, Cumuliform clouds Shower type precipitation (Hail and thunderstorms may occur) What are the three main source regions for North America? Arctic (Cold), Polar (Cool), Tropical (Warm) What are the two air mass sub-categories? Maritime and continental Name some factors that affect air masses