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Ever heard of a Temperate Cyclone?. Weather Systems & Air Masses. Weather System – recurring circulation pattern & associated weather Air mass – large bodies of air with uniform temp & moisture Up to thousands of km across May extend up to top of troposphere Measured by: Surface temperature
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Weather Systems & Air Masses • Weather System – recurring circulation pattern & associated weather • Air mass – large bodies of air with uniform temp & moisture • Up to thousands of km across • May extend up to top of troposphere • Measured by: • Surface temperature • Environmental lapse rate • Surface specific humidity
Air Masses • Develop over source regions • Take on characteristics of the region • Air masses classified by: • Latitude (Arctic (A), polar (P), tropical (T), equatorial (E)) • Indicate temperature • Surface type (Maritime (m), continental (c)) • Indicate moisture content
Source Regions • Idealized continent & oceans show source regions for air masses • Combined air mass labels (no cE, mA or mAA) • mE, mT, cT, mP, cP, cA, cAA
Fronts • Surface of contact between 2 distinct air masses • E.g. boundary between polar & tropical air → polar front
Fronts • Cold Front – moving front → cold air mass moves under warm air mass • Cold front stimulates cumulonimbus clouds & T-storms
Fronts • Warm Front – moving front → warm air slides over cold air • Slower than cold front • Warm front stimulates nimbostratus clouds & rain
Anticyclones • High pressure • Fair weather system • Descending air warms adiabatically • No condensation • Little pressure gradient in center of high • Winds light & variable
Cyclones • Converging, inspiraling air rises → condensation • Cyclonic storm: • Intense convection • Strong winds • Heavy precipitation • 3 types of traveling cyclones: • Midlatitude cyclone (or extratropical cyclone) • Tropical cyclone • Tornado
A “Perfect Storm” • Intense cyclonic storm • L marks the center of rotation • Strong wind & precip hit NE US (blue & orange) L
Midlatitude Cyclones • Dominant weather systems in mid & high latitudes • Form, intensify and dissolve along polar front • Air converging along front can create circulation • Cyclone may last a few days, moving west-to-east • May drag cold front S or SW of low • Warm front E or SE of low • Cold front overtakes warm front → occluded front
Upper-Air Disturbances • Closely related to midlatitude cyclone development at surface • Upper-air convergence → high surface pressure • Upper-air divergence → low surface pressure
Cyclone Tracks & Families • Certain regions good to develop cyclones • Upper-level winds consistently steer cyclones • So, consistent cyclone tracks are well known • Sets of tracks form cyclone families Midlatitude Cyclone Tracks
Cold Air Outbreaks • Occasionally cold air from polar regions pushes far south • This February image shows cold, clear air as far south as Florida • White pattern E & SE of image is clouds from cold front • White in NW of image is snow cover