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Chapter 9 – Air Masses and Fronts Understanding Weather and Climate Aguado and Burt ATMO 1300 Air Masses and Fronts • Air masses are defined by temperature, pressure and moisture characteristics • Fronts are fairly narrow boundaries that separate different air masses ATMO 1300 1 Air Mass Characterization • Classified according to temperature and moisture characteristics. – – – – – Continental (dry) - c Moisture Maritime (moist) - m Tropical (warm) - T Temperature Polar (cold) - P Artic (extremely cold) - A ATMO 1300 Air Mass Source Regions • Source Regions – areas of the globe where air masses form ATMO 1300 2 Continental Polar (cP)/Continental Artic (cA) • Continental Polar - form over large, high-latitude land masses – Low temperatures – Low moisture content – Cooling of air from below also leads to radiation inversions and highly stable conditions. – Few clouds • Continental Artic – colder than polar ATMO 1300 Artic and Polar Fronts • cA and cP air is separated by the Artic front ATMO 1300 3 Maritime Polar (mP) • Maritime Polar - forms over North Pacific and North Atlantic – Low temperatures – Lower moisture content – Similar to Continental Polar, but more moderate with respect to temperature and moisture. ATMO 1300 Continental Tropical (cT) • Continental Tropical - forms in the summer over low-latitude areas. – – – – Warm temperatures Limited moisture Highly unstable due to extreme surface heating Cloud free due to lack of moisture ATMO 1300 4 Maritime Tropical (mT) • Maritime Tropical - develop over warm tropical waters – – – – Warm temperatures Moist Unstable Ideal for precipitation and clouds ATMO 1300 Fronts • Cold Front - cold air advancing towards warm air • Warm Front –warm air moving towards cold air • Stationary Front – not moving • Occluded Front – surface fronts between two polar air masses ATMO 1300 5 Cold Fronts ATMO 1300 Warm Fronts ATMO 1300 6 Stationary Front • Non-moving boundaries • Identical to cold and warm fronts with sloping boundary over the cold air. ATMO 1300 Occluded Fronts ATMO 1300 7 Occluded Fronts ATMO 1300 Occluded Fronts ATMO 1300 8 Occluded Fronts • Cold front moves eastward relative to the warm front. ATMO 1300 Drylines ATMO 1300 9
