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1 Weather includes short term changes in temperature, precipitation, pressure, volume and density of the air. Long term weather, defined as 30 years, is called climate. 2 Weather occurs in the troposphere. This part of the atmosphere has 75% of the atmosphere's mass and most of the water vapor to form clouds, thunderstorms, tornadoes, hurricanes, and blizzards. 3 Charles' Law says there is a direct relationship between temperature and volume. Temperature is the result of variations in solar energy unevenly heating the atmosphere and the tilt of Earth on its axis, that provides seasons. With a fixed amount of gas, when the temperature is increased, the volume is increased. Simply put, gases expand when heated. 4 Warm air rises and expands carrying more water vapor. The air becomes less dense and creates low pressure. Asair airrises risesititcools. cools. Cold Coldair airholds holdsless lesswater watervapor vaporthan thanwarm warm As air,so sowater wateris isreleased releasedas asprecipitation precipitation.and giant convection cells air, circulate air currents in the atmosphere. 5 The rotation of the earth gives air masses their properties. Because air doesn’t heat evenly, wind is created. Winds create climate, circulate heat, moisture and nutrients across the earth, but they also transport pollution. Winds are moved around the earth by the daily rotation and the yearly revolution around the sun. 6 As temperature increase, the evaporation rate increases and the volume of water contained in the air increases. Relative humidity is a term used to describe the amount of water vapor that exists in the atmosphere. It is “relative “ to 100% saturation. As water vapor it rises to form clouds. 7 Clouds will form when the dew point of water is reached in the presence of any small non-gaseous particle – water droplet, ice crystals, dust, soot, salt, or pollution. Cloud seeding artificially add particles as cloud condensation nuclei. Dew point is the temperature when atmospheric humidity reaches 100% and the air is fully saturated. Clouds usually look white because they reflect the same amount of 8 all of the colors of visible light. Thick, low-lying clouds appear gray because sunlight does not fully penetrate and the amount of water vapor scatters the short blue-gray wavelengths. 9 At sunrise and sunset clouds may appear reddish because long, low energy, wavelengths of sunlight are scattered and reflected in low clouds. 10 There are basically four types of clouds. However, dozens of combinations define very specific cloud formations at various altitudes. The names, derived from Latin, describe the way clouds look. 1. Cumulus - heap, puffy 2. Stratus - layered 3. Cirrus - curls, wispy 4. Nimbus – cloud, rain storm 11 Cloud are grouped by their altitude of the bottom section. Family A. - Prefix Cirrus High altitude clouds occur above 20,000 ft. They appear white, thin and wispy and indicate good weather. Family B. - Prefix Alto Middle altitude clouds appear between 6,500 to 20,000 ft. and are more gray from increased water vapor. Rain may develop. 12 Family C. – Prefix Cumulo or Strato Low altitude cloud that form on the ground up to 6,500 ft Clouds can be more accurately described by combining the descriptive names such as Stratocumulus or Cumulonimbus. Sometimes cloud form vertically. Altostratus Cumulonimbus 13 14 Contrails are condensation trails left behind jet aircrafts. Contrails form when hot humid air from jet exhaust mixes with air of low vapor pressure and low temperature. 15 The forms of precipitation: •Rain - condensation of atmospheric water vapor •Hail - Thunderstorm updrafts carry water droplets high into the atmosphere where they can freeze multiple times. •Snow - Water droplets form and then freezing occurs slowly. •Sleet - Rain freezes somewhere between the clouds and the ground. •Frost - Dew forms and then it freezes. •Ice - Rain freezes on contact with the ground. •Fog - Temperature equals the dew point. 16