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Unformatted text preview: Exam 3 Dec 10 th Air Masses and Fronts o Air masses Contain uniform humidity characteristics Affect vast areas o Fronts Boundaries between air masses Spatially limited Linked to mid-latitude cyclones o Source regions Topographically-uniform sites of air mass formation Typical formation occurs when air stagnates over large surface regions Overlying air gains temperature and moisture characteristics of surface o Air mass moisture classification, from wettest to driest: Maritime ( m )-wet Continental ( c )-dry o Air mass temperature classification, from warmest to coolest: Tropical ( T )-warm Polar ( P )-cold Arctic ( A )-very cold Movement of Air Masses o Move with general atmospheric circulation o Displace existing air over locations and change surface weather characteristics (temp, humidity, etc) o Continually affected by surface influences Continental Polar ( c P ) and Continental Arctic ( c A ) o Continental Polar ( c P ) Source region Northern Canada Characteristics Cold, dry, stable; slightly warmer and more humid during summer o Continental Arctic ( c A ) Source region Above Arctic Circle Characteristics Extremely cold and very dry o The boundary between c P and c A is the Arctic Circle Maritime Polar ( m P ) Air Masses Source regions Northern Atlantic and Pacific Basins Characteristics Cool and moist o m P air masses are often found along the West Coast ahead of mid-latitude cyclones and along the East Coast behind cyclones Noreasters Continental Tropical ( c T ) Air Masses Source regions Southwest U.S. and northern Mexico Characteristics Hot and very dry o Very unstable but produce little precipitation due to lack of water vapor o Thunderstorms may occur with moisture advection or orographic lifting Maritime Tropical ( m T ) Air Masses Source regions Warm ocean basins (e.g., Gulf of Mexico) Characteristics Very warm, very humid, very unstable o Advection of m T across continent during the summer Can lead to high heat indices Causes NAMS North American Monsoon System Fronts Separate air masses Bring about changes in temperature and humidity Associated with mid-latitude cyclones Naming reflects advancing air mass type o Cold Fronts Form when cold air displaces warm air steeply upward Associated with heavy, brief precipitation and rapid temperature drops Cumulonimbus clouds Sharp cold front boundaries are evident on satellite and radar images o Warm Fronts Warm (usually moist) air moves aloft over cool (usually drier) air Overrunning Light, steady precipitation from stratus-type clouds Also possible fog, sleet, freezing rain o Stationary Fronts Two unlike air masses remaining side by side, with neither encroaching Identified by temperature differences on either side of the front May slowly migrate; warmer air may be displaced above cooler air...
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- Fall '07