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The Temperate Climate The Temperate Hadley Cell • Westerly Prevailing Winds • Warm inputs (often from the Tropical Hadley Cell) • Cold inputs form the Polar Hadley Cell • Weather develops where the cold and warm inputs collide guided by the Jet Stream 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: • Temperature • 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 The Pineapple express Cold dry air from Alaska Warm moist air from Hawaii Fronts • Surface of contact between 2 distinct air masses – E.g. boundary between polar & tropical air → polar front Fronts • Cold air is heavier than warm air….the warm air is pushed over the cold air Fronts • Warm Front – moving front → warm air slides over cold air – Slower than cold front – Warm front stimulates nimbostratus clouds & rain 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 • High pressure • Fair weather system • Descending air warms adiabatically • No condensation Anticyclones 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-toeast Lifecycle of Midlatitude Cyclone 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