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Atmospheric Water and Weather • • • • • • • • Water on Earth Humidity Atmospheric Stability Clouds and Fog Air Masses Atmospheric Li=ing Mechanisms Midla>tude Cyclonic Systems Violent Weather Water on Earth • • • • Quan4ty Equilibrium Distribu4on of Earth’s Water Today Unique Proper4es of Water Heat Proper4es – Ice – Water – Water vapor – Heat proper4es of water in nature Heat Proper4es of Water • Heat Proper4es – Ice – Water – Water Vapor • Phase Change 1 FOR WATER TO CHANGE STATES . . . HEAT ENERGY MUST BE ABSORBED OR LIBERATED THE AMOUNT OF HEAT ENERGY MUST BE ENOUGH TO AFFECT THE HYDROGEN BONDS IN WATER MOLECULES THIS WATER/HEAT RELATIONSHIP IS A DRIVING FORCE IN PRODUCING WEATHER . . . PROVIDING 30% OF THE ENERGY THAT POWERS THE GENERAL CIRCULATION OF THE ATMOSPHERE THIS CHANGING OF STATES IS KNOWN AS PHASE CHANGE . . . THE CHANGE IN PHASE, OR STATE, AMONG ICE, WATER, AND WATER VAPOR . . . INVOLVING THE ABSORPTION OR RELEASE OF LATENT HEAT INCLUDES MELTING AND FREEZING . . . AND CONDENSATION AND EVAPORATION HEAT ENERGY IS ABSORBED AS THE LATENT HEAT . . . OF MELTING . . . VAPORIZATION . . . OR EVAPORATION HEAT ENERGY IS RELEASED AS THE LATENT HEAT OF CONDENSATION . . . AND FREEZING 2 Humidity • Rela4ve Humidity – Satura4on – Dew Point HUMIDITY HUMIDITY IS THE WATER VAPOR CONTENT OF THE AIR THE CAPACITY OF THE AIR TO HOLD WATER IS MOSTLY A FUNCTION OF THE TEMPERATURE OF THE AIR WARMER AIR HAS A GREATER CAPACITY FOR HOLDING WATER THAN COOL AIR WARM AIR STORES A GREATER AMOUNT OF ENERGY IN THE ATMOSPHERE THAN COLDER AIR THUS . . . THE WARMTH OF THE AIR ENABLES THE ATMOSPHERE TO HOLD MORE MOISTURE 3 RELATIVE HUMIDITY IS THE RATIO OF WATER VAPOR ACTUALLY IN THE AIR (THE CONTENT) . . . COMPARED TO THE MAXIMUM WATER VAPOR THE AIR COULD HOLD (ITS CAPACITY) AT THAT TEMPERATURE IT IS EXPRESSED AS A PERCENTAGE IF AIR IS DRY THE RELATIVE HUMIDITY PERCENTAGE IS LOW IF THE AIR IS MOIST THE RELATIVE HUMIDITY IS HIGHER IF THE AIR CANNOT HOLD ANY MORE MOISTURE IT IS SATURATED AND THE RELATIVE HUMIDITY IS 100% Atmospheric Stability • Adiaba4c Processes • Stable and Unstable Atmospheric Condi4ons 4 Adiaba4c Processes • Dry adiaba4c rate – 10 C°/ 1000 m – 5.5 F°/ 1000 O • Moist adiaba4c rate – 6 C°/ 1000 m – 3.3 F°/ 1000 O REMEMBER . . . AN ASCENDING AIR PARCEL COOLS BY EXPANSION . . . RESULTING FROM THE REDUCED AIR PRESSURE AT HIGHER ALTITUDES A DESCENDING AIR PARCEL HEATS BY COMPRESSION . . . RESULTING FROM THE INCREASED AIR PRESSURE AT LOWER ALTITUDES Clouds and Fog • Cloud Types and Iden4fica4on • Fog – Advec4on Fog – Radia4on Fog 5 CLOUDS THAT DEVELOP HORIZONTALLY AND ARE FLAT AND LAYERED ARE STRATIFORM CLOUDS CLOUDS THAT ARE DEVELOPED VERTICALLY AND ARE PUFFY AND GLOBULAR ARE CUMULIFORM CLOUDS HIGH-ALTITUDE, WISPY CLOUDS COMPOSED OF ICE CRYSTALS ARE CIRROFORM CLOUDS Fog • • • • • Advec4on fog Evapora4on fog Upslope fog Valley fog Radia4on fog Atmospheric LiOing Mechanisms • Convec4onal LiOing • Orographic LiOing • Frontal LiOing – Cold Fronts – Warm Fronts 6 Frontal LiOing • Cold Fronts – Cold air forces warm air aloO – 400 km wide (250 mi) • Warm Fronts – Warm air moves up and over cold air – 1000 km wide (600 mi) Violent Weather • Thunderstorms • Tornadoes • Tropical Cyclones 7