Fronts Mountains Heat Capacity Latent Heat The Weather Clouds and Rain Cloud formation and precipitation is determined ultimately by the vertical movement of air. Upward motion enhances cloud formation Cloud formation leads to rainfall. Warm air holds more moisture than cold air. As warm air rises, it cools and cannot hold moisture Clouds Clouds form when moisture condenses from the atmosphere. When the moisture in clouds is sufficiently abundant, raindrops or snow falls to the earths surface. Clouds form when moisture condenses from the atmosphere. When the moisture in clouds is sufficiently abundant, raindrops or snow falls to the earths surface. If clouds are condensed moisture (liquid water), how do clouds float in the air? How do Clouds Float? Size: 10 micons Velocity: 0.3 cm/sec or 10 meters/hr ETA: 350 hours (3500 m or 10,500 ft) Updrafts Evaporation Terminal Velocity Updrafts Evaporation Terminal Velocity It takes about 15 million cloud droplets to form the typical raindrop 120 to 200 mph Precipitation: Rainfall 70% of earth surface covered by oceans Ocean evaporation accounts for 90% of precipitation. 10% to land 90% to Oceans Residence time in atmosphere: 14 days Evaporation 4,200 bgd Rainfall Rainfall and Rainfall Types Frontal Orographic Convective Frontal Two masses of air of different temperature, humidity and density meet Warm air is lighter than cool air. Warm air rises over cool air. Cold Fronts and Warm Fronts Orographic Rainfall Warm moisture-laden wind blowing in to the land from the sea encounters a natural barrier Warm Moist air Air cools Rainfall Dry Air mountain Prevailing wind Ocean Orographic Lifting High rainfall Low rainfall Prevailing wind Rain shadow wet dry 39 18 110 The Mojave Desert Sierra-Nevada ,000 ft. Convective Rising of warm, moist air due to surface heating Equatorial Regions Florida Southeast Sun warms water or land Low pressure cools High Amounts of Solar Heating Moist Air Where? When? Hurricanes are Convective Storms Hurricane season = June - November * When? June o September equator 30 o N wind Atlantic Hurricanes develop between 8 o and 20 o latitude Warm water and Coriolis circulation Solar heat Warms water Water Evaporates 580 cal/g heat Cooling and Rainfall Releases 580 cal/g of heat Ordinary Thunderstorm Rising moist air Contains 580 cal/g heat. Low Pressure inflow Cooling and Condensation Release of latent heat (580 Cal/g) Condensation and release of latent heat (580 Cal/g) Rising air Intensifies Rising moist air Low Pressure inflow Condensation and release of latent heat (580 Cal/g) Condensation and release of latent heat (580 Cal/g) Increasing pressure vent Tropical Disturbance Large cluster of thunderstorms forming over tropical waters. Intensify or Dissipate 1 st sign of hurricane genesis Tropical Storm Lower pressure Organization and cyclonic circulation Heat Moisture Circulation Low pressure Warm moist air Hurricane Pressure: mbars is normal, 882 is record. Hurricane Formation as Convective Storms Cyclonic Easterly wind Category 1 -- Winds mph Category 2 -- Winds mph Category 3 -- Winds mph Category 4 -- Winds mph Category 5 -- Winds over 155 mph. Central Pressure pressure at the center of the storm low pressures indicate strong storms Wind shear upper level winds which can prevent rapid rising of air and decreased pressure Tropical Storm cyclone in which the maximum sustained surface wind speed ranges from 39 mph to73 mph Tropical depression a closed low pressure area with organized convection, heavy rain, and winds up to 38 mph Hurricanes: Saffir-Simpson Scale Wind Shear Wind shear or high upper level winds can dissipate a hurricane Cooler water can also dissipate a hurricane Extra Credit Question: Identify the 3 types of rainfall discussed. Answer on the back of the lecture question sheet (You may use your notes) Other Extreme Weather