Cloud Fraction
In addition to their role as rain- and snow-makers in Earth's water cycle, clouds play a major part in Earth's energy budget—the balance of energy that enters and leaves the climate system. Clouds may have a warming or cooling influence depending on their altitude, type, and when they form.
Clouds reflect sunlight back into space, which causes cooling. But they can also absorb heat that radiates from the Earth's surface, preventing it from freely escaping to space. One of the biggest sources of uncertainty in computer models that predict future climate is how clouds influence the climate system and how their role might change as the climate warms.
Global maps show what fraction of an area was cloudy on average each month. The measurements were collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. Colors range from blue (no clouds) to white (totally cloudy). Like a digital camera, MODIS collects information in gridded boxes, or pixels. Cloud fraction is the portion of each pixel that is covered by clouds. Colors range from blue (no clouds) to white (totally cloudy).
From month to month, a band of clouds girdles the equator. This band of persistent clouds is called the Intertropical Convergence Zone, the place where the easterly trade winds in the Northern and Southern Hemispheres meet. The meeting of the winds pushes warm, moist air high into the atmosphere. The air expands and cools, and the water vapor condenses into clouds and rain. The cloud band shifts slightly north and south of the equator with the seasons. In tropical countries, this shifting of the Intertropical Convergence Zone is what causes rainy and dry seasons.
Another frequently cloudy place is the Southern Ocean. Although there is not as much evaporation in the high latitudes as in the tropics, the air is cold. The colder the air, the more readily any water vapor in the air will condense into clouds.
View, download, or analyze more of these data from NASA Earth Observations (NEO): Cloud Fraction
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The Hydrologic Cycle - A Multi-Phased Journey
Education
Many people benefit from knowledge and interesting facts...Did You Know?
When precipitation falls over the land surface, it follows various routes. Some of it evaporates, returning to the atmosphere, and some seeps into the ground (as soil moisture or groundwater). Groundwater is found in two layers of the soil, the "zone of aeration," where gaps in the soil are filled with both air and water, and, further down, the "zone of saturation," where the gaps are completely filled with water. The boundary between the two zones is known as the water table, which rises or falls as the amount of groundwater increases or decreases.
The water table is the top of the zone of saturation and intersects the land surface at lakes and streams. Above the water table lies the zone of aeration and soil moisture belt, which supplies much of the water needed by plants.
Throughout the hydrologic cycle, there are an endless number of paths that a water molecule might follow.