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World & Indian (Atmospheric Dynamics)

Written By STPORTAL on Sunday, March 18, 2012 | 2:56 PM

- World & Indian (Atmospheric Dynamics):

Between thirty and sixty degrees latitude, the winds that move toward the poles appear to curve to the east. Because winds are named from the direction in which they originate, these winds are called prevailing westerlies. Prevailing westerlies in the Northern Hemisphere are responsible for many of the weather movements across the United States and Canada.

At about sixty degrees latitude in both hemispheres, the prevailing westerlies join with polar easterlies to reduce upward motion. The polar easterlies form when the atmosphere over the poles cools. This cool air then sinks and spreads over the surface. As the air flows away from the poles, it is turned to the west by the Coriolis effect. Again, because these winds begin in the east, they are called easterlies. Many of these changes in wind direction are hard to visualize. Complete this exercise to see the pattern of the winds.

Jet Streams
Narrow belts of high speed winds that blow in the upper troposphere and lower stratosphere. The polar jet stream also marks the presence of Rossby waves, long-scale (4000 - 6000 km in wavelength) harmonic waves which perpetuate around the globe.

Seasonal winds
Seasonal winds are winds that only exist during specific seasons, for example, the Indian monsoon.

Synoptic winds are winds associated with large-scale events such as warm and cold fronts, and are part of what makes up everyday weather. These include the geostrophic wind, the gradient wind, and the cyclostrophic wind.

As a result of the Coriolis force, winds in the northern hemisphere always flow clockwise (when seen from above) around a high pressure area and counterclockwise around a low pressure area (the reverse occurs in the southern hemisphere).

Local winds
Some local winds blow only under certain circumstances, i.e. they require a certain temperature distribution. The following are the examples
  • Sea Breeze --> A cool breeze blowing from the sea toward the land.
  • land breeze --> A breeze that blows from the land toward open water.
  • A katabatic wind --> derived from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. Such winds, particularly when they occur over a wide area, are sometimes called fall winds.
  • Aanabatic wind --> The opposite of a katabatic wind is an anabatic wind, or an upward-moving wind.
  • Mountain wind -->A breeze that blows down a mountain slope due to the gravitational flow of cooled air.
  • Valley wind --> A gentle wind blowing up a valley or mountain slope in the absence of cyclonic or anticyclonic winds, caused by the warming of the mountainside and valley floor by the sun.

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