At night the mountain slopes cool more quickly than the nearby valley, which causes a mountain breeze to flow downhill. Katabatic winds move up and down slopes, but they are stronger mountain and valley breezes. Katabatic winds form over a high land area, like a high plateau. The plateau is usually surrounded on almost all sides by mountains.
In winter, the plateau grows cold. The air above the plateau grows cold and sinks down from the plateau through gaps in the mountains. Wind speeds depend on the difference in air pressure over the plateau and over the surroundings. Katabatic winds form over many continental areas. Extremely cold katabatic winds blow over Antarctica and Greenland. Chinook winds or Foehn winds develop when air is forced up over a mountain range.
This takes place, for example, when the westerly winds bring air from the Pacific Ocean over the Sierra Nevada Mountains in California. As the relatively warm, moist air rises over the windward side of the mountains, it cools and contracts. If the air is humid, it may form clouds and drop rain or snow.
When the air sinks on the leeward side of the mountains, it forms a high pressure zone. The windward side of a mountain range is the side that receives the wind; the leeward side is the side where air sinks. The descending air warms and creates strong, dry winds. Snow on the leeward side of the mountain disappears melts quickly. If precipitation falls as the air rises over the mountains, the air will be dry as it sinks on the leeward size.
As air rises over a mountain it cools and loses moisture, then warms by compression on the leeward side. The resulting warm and dry winds are Chinook winds. The leeward side of the mountain experiences rainshadow effect.
Santa Ana winds are created in the late fall and winter when the Great Basin east of the Sierra Nevada cools, creating a high pressure zone. The high pressure forces winds downhill and in a clockwise direction because of Coriolis. The air pressure rises, so temperature rises and humidity falls. The winds blow across the Southwestern deserts and then race downhill and westward toward the ocean.
The winds are especially fast through Santa Ana Canyon, for which they are named. Santa Ana winds blow dust and smoke westward over the Pacific from Southern California.
The hot, dry winds dry out the landscape even more. If a fire starts, it can spread quickly, causing large-scale devastation Figure below. In October , Santa Ana winds fueled many fires that together burned , acres of wild land and more than 1, homes in Southern California.
High summer temperatures on the desert create high winds, which are often associated with monsoon storms. Desert winds pick up dust because there is not as much vegetation to hold down the dirt and sand. Figure below. A haboob forms in the downdrafts on the front of a thunderstorm. Dust devils, also called whirlwinds, form as the ground becomes so hot that the air above it heats and rises.
Air flows into the low pressure and begins to spin. Dust devils are small and short-lived but they may cause damage. Because more solar energy hits the equator, the air warms and forms a low pressure zone.
At the top of the troposphere, half moves toward the North Pole and half toward the South Pole. As it moves along the top of the troposphere it cools. The cool air is dense and when it reaches a high pressure zone it sinks to the ground. Carbon dioxide is present in small amounts, but its concentration has nearly doubled since Like water vapor, carbon dioxide is a greenhouse gas which traps some of the Earth's heat close to the surface and prevents its release into space.
Scientists fear that the increasing amounts of carbon dioxide could raise the Earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans. The uneven heating of the regions of the troposphere by the sun the sun warms the air at the equator more than the air at the poles causes convection currents, large-scale patterns of winds that move heat and moisture around the globe.
In the Northern and Southern hemispheres, air rises along the equator and subpolar latitude about 50 to about 70 north and south climatic regions and sinks in the polar and subtropical regions. Air is deflected by the Earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west easterly winds in tropical and polar regions, the winds moving from west to east westerly winds in the middle latitudes.
This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence. A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat.
Smog is produced when pollutants accumulate close to the surface beneath an inversion layer a layer of air in which the usual rule that temperature of air decreases with altitude doesn't apply , and undergo a series of chemical reactions in the presence pollutants from escaping into the upper atmosphere.
Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection. The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind. Why is the atmospheric pressure less at the poles?
What are pressure conditions of air above the equator? Is air pressure near the equator greater than air pressure near the poles? What kind of pressure does the air masses at the poles? The air above the poles is? How does air travel at the poles? Air pressure near the equator is less than air pressure at the poles a fact that causes air to move where? Why is the altitude of the tropopause lower above the poles than above the equator?
What is local atmospheric pressure? How does differences in air pressure puts air in motion? Why is there high air pressure at the poles? Would you expect high or low air pressure at he poles?
What happens to the pressure of air as the air rises? What effects air pressure? Does air pressure increases with elevation? What is the cause of differences in air pressure? Why is the air pressure the poles higher than the air pressure at the equator? Why is the air pressure at the poles higher than the air pressure at the equator? Would you expect high or low air pressure at the poles? Is air pressure greater when your higher up or lower?
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