M ountains can have a significant effect on rainfall. When air reaches the mountains, it is forced to rise over this barrier. As the air moves up the windward side of a mountain, it cools, and the volume decreases. As a result, humidity increases and orographic clouds and precipitation can develop. As air flows over mountains it is forced higher into the atmosphere. Air is blown towards the bottom of a large hill or mountain and has to to move up and over the obstacle.
The decrease in temperature causes water vapour within the air to condense and, under the right conditions, can create precipitation. The dominant wind patterns force air to go up and over the mountain. As the air rises it cools and the moisture in the air condenses and falls as precipitation. The side of the mountain that the air has been forced up receives more precipitation, leaving the opposite mountainside drier.
They receive more rainfall than low lying areas because the temperature on top of mountains is lower than the temperature at sea level. Winds carry moist air over the land. When air reaches the mountain, it rises because the mountains are in the way. The uppermost level of mountains is often bare rock and snow. Tibet and the Himalayas and other mountain ranges such as the Rocky Mountains or the Andes are good examples of this. You can often see snow on the top of mountains all year round, because the temperature at the top of mountains is lower than at the bottom.
The higher the place is above sea level the colder it will be. Some mountains reach higher than the clouds. At this altitude the extreme cold and high winds cause blizzards. Generally the climate on mountains get progressively colder with increased altitude the higher up you go. This happens because as altitude increases, air becomes thinner and is less able to absorb and retain heat. The cooler the temperature the less evaporation there is, meaning that there is more moisture in the air.
Air pressure decreases with altitude. As a result of the reduced air pressure, rising air expands and cools. Mountains can affect the climate of nearby lands. In some areas, mountains block rain, so that one side of a mountain range may be rainy and the other side may be a desert. Rain Shadow Much of airborne moisture falls as rain on the windward side of mountains. This often means that the land on the other side of the mountain the leeward side gets far less rain—an effect called a "rain shadow"—which often produces a desert.
The higher the mountain, the more pronounced the rain shadow effect is and the less likely rain will fall on the leeward side. As the air continues moving to the east, it plunges down the other side of the mountains, warms up, and dries out. This phenomenon causes areas on the west side of the mountains to be much wetter than areas on the east side.
Meteorologists call this contrast the orographic effect. The higher the elevation of a place, the cooler its temperature tends to be. Here in western North Carolina, Asheville is located in a broad valley surrounded by high mountain peaks. The elevation of Asheville is about 2, feet above sea level. Twenty miles to the northeast, Mount Mitchell, at 6, feet above sea level, is the highest peak in the eastern United States. The sharp elevation change over such a short distance means the average temperature for the two seemingly nearby locations is very different.
The annual average temperature in Asheville is When calculating climate variables for an area, like we do in our climate division dataset , we must take into account these temperature and precipitation changes due to topography. We do this by two methods described below.
For the U. The process of putting the data onto the grid utilizes our knowledge of how temperature and precipitation behave with elevation changes. Based on mathematical formulas we can determine best estimates of the temperature and precipitation between those two locations. This provides a better spatial representation of weather and climate data across the region. Another way take into account changes in topography is by using anomalies.
Temperature anomalies change less over a distance than the absolute temperature, regardless of topography.
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