Goals and Design
Predicting weather change requires accurate data that is collected over many years, and the application of models. GEWEX was conceived to respond to the need for observations of the Earth's radiation budget and clouds. Many preexisting techniques were limited to observations taken from land and populated areas. This ignored the large amount of weather that occurs over the oceans and unpopulated regions, with key data missing from these areas. Since satellites orbiting the earth cover large areas in small time frames, they can better estimate climate where measurements are infrequently taken. GEWEX was initiated by World Climate Research Programme (WCRP) to take advantage of environmental satellites such as TRMM, but now uses information from newer satellites as well as collections land based instruments, such as BSRN. These land based instruments can be used to verify information interpreted from satellite. GEWEX studies the long-term and regional changes in climate with a goal of predicting important seasonal weather patterns and climate changes that occurs over a few years.
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Radiation, Humidity, and Aerosols
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| Sunlight and Rain |
The earth as an object is made of matter, including water, which absorbs and emits energy into space. Should the earth not orbit a star, the water would freeze solid and little precipitation would occur because the rate of evaporation would be very low. If the earth were devoid of water, it would heat to great temperatures in the daytime and cool off more quickly at night. Therefore, water modulates heat energy by transitioning between ice, water, and steam. When heat is applies ice becomes water and water becomes vapor-steam, absorbing heat energy. When cooling is applied vapor condenses it to water and water freezes into ice, releasing heat. While these are simple examples, rainfall results from a complex set of processes. When sunlight hits the oceans it forces liquid water into the vapor state at a rate dependent on surface temperatures, humidity, winds and pressure. At equilibration water reaches 100% humidity and during the day the temperature rises allowing more moisture to accumulate in the air. At night the temperature falls and water tends to form clouds often resulting in ground fog in coastal areas.
At 100% humidity any loss of radiant energy from water causes vapor to condense into water. Circulation and convection can carry moist air upward in the air column, and this often cools moist air. The air forms water droplets, even in the heat of daytime, making clouds. As the density of droplets in the clouds increase the air can no longer support droplets and they fall as rain. More moist air can be drawn into clouds as energy is release allowing the development of large thunderstorms. Prevailing winds are a factor in storm formation, particularly when changes occur. Tropical waves that develop in westerly flows around the Earths semitropical and tropical region can organize into horizontal circles over the water, creating a cyclone.
A cyclone is a stereotype energy transfer system, it gathers steam off of warm water, and quickly moves it upwards releasing the energy into space, this causes the characteristic rain bands. The energy transferred is so great it gives rise to catastrophic winds, which disturb surface waters increasing steam release and also increase the rate moisture is drawn into the center. The heat of the water under the storm drops. Cyclones demonstrate how much latent energy is stored in the world's oceans.
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| Fluxes, Radiation and Aerosols |
| The moisture for a cyclone can be defined as the warm water below the storm, as the cyclone leaves warm water its energy dissipates quickly. Less powerful, long term rainfall generators can rely on moisture driven by warm waters far from greatest region of rainfall. In the tropics the energy came from, stored heat in ocean currents and moving thermoclines can provide sources far away, such as is seen in El-nino.
Other examples are the floods that hit the midwest in 1993, the energy that drove moisture into the air occurred in the gulf, and strong winds and lack of cooling in coastal regions permitted the moisture to travel 1000 miles until conditions were ripe for rain, as the rain fell it cooled the air and dissipated heat and as new moisture arrive the process continued. When the sun did come out it heated wet ground and this created more rain.
Aerosols over the ocean can cause a lack of sufficient heat in the middle of the day to create sufficiently humid air, and when the air reaches land, which may be warmer, there may be inadequate convection and other processes to create rains, and this can cause droughts. To better see these events progress scientist need data and to create models to see what elements of the data are most useful in determining rainfall. |
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