The amount of moisture in the air is also commonly reported as relative humidity which is the percentage of the total water vapor air can hold at a particular air temperature. Rainfall amounts can be estimated by weather radar.Īir contains water vapor, and the amount of water in a given mass of dry air, known as the mixing ratio, is measured in grams of water per kilogram of dry air (g/kg). Climate classification systems such as the Köppen classification system use average annual rainfall to help differentiate between differing climate regimes. The globally averaged annual precipitation over land is 715 mm (28.1 in), but over the whole Earth, it is much higher at 990 mm (39 in). Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics.
The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities.
The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity.
0 kommentar(er)
