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Evaporation
Earth is unique because its temperatures allow water to exist in its liquid form; the majority of water is in liquid form in the oceans. However, the atmosphere also houses water in the form of water vapor. As water heats up, it evaporates. Sunlight provides a constant source of heat and continually makes bodies of water warmer, causing them to evaporate into the atmosphere. Warm air rises into the troposphere, the lowest portion of earth's atmosphere. Areas that receive more sunlight experience more evaporation. Water also transpires from plants' leaves into the air.
Condensation
Water vapor is hotter than the surrounding atmosphere, so it is less dense and able to rise in the cooler air. When the water vapor rises to a certain point, it begins to cool and condense into clouds. These clouds contain both liquid water droplets and ice crystals; they are small enough to be held up by the surrounding air. Clouds become larger as more water evaporates and is absorbed into them.
Transportation
Clouds that get caught in large air currents flow with the currents. The air currents of earth's atmosphere exist largely as patterns called Hadley cells. Warm air rises and flows from the equator toward the poles, deflected westward by the Coriolis effect. Conversely, cool air that sinks flows from the poles toward the equator and is similarly deflected. Cloud systems form mostly over the oceans and make their way to land, where cooler air causes further condensation of cloud water.
Precipitation
Rain, snow, hail and sleet are all different forms of precipitation, dependent on temperature. It occurs when water droplets become too large and heavy to remain suspended in the air and fall back to the ground. In the case of hail, ice pellets fall, get caught in updrafts and grow larger when more ice appears. Factors that influence local precipitation include temperature and geography. Cooler areas have less precipitation because any existing water is less likely to evaporate and condense into clouds. Geographical features such as mountains affect precipitation by blocking clouds and wind from passing into an adjacent valley.
Groundwater and Runoff
Once water falls to land, it has to make its way back to the ocean, where the cycle can begin again. This can happen through groundwater, which is water that flows downward through soil, and through runoff, which is surface flow in the form of rivers and lakes.