AIR MASSES OVER ASIA 

The air masses commonly observed over Asia (especially eastern Asia) are continental polar, maritime tropical, and equatorial. Maritime polar and continental tropical air play a minor part in the air mass cycle of Asia.

Continental polar air, as observed over the in-terior of Asia, is the coldest air on record in the Northern Hemisphere. This is brought about by the fact that the interior of Asia, made up of vast level and treeless regions, serves as an ideal source region. The Himalaya mountain range, across southern Asia, aids in the production of cP air. It tends to keep the polar air over the source region for a long time and to block the inflow of tropical air from the lower latitudes.

The weather conditions over eastern Asia are governed by this air mass throughout the winter. Successive outbreaks of this air occur over Siberia, China, and the Japanese Islands and establish the winter weather pattern. The weather conditions prevailing in this air are similar to those found in cP air over the eastern portion of North America.

The cold air that is forced southward over the Himalaya Mountains to India and Burma arrives in a highly modified form and is known as the winter monsoon.

The weather conditions during the winter monsoon are dominated by the dry and adiabatically warmed polar air flowing equator-ward. It is while under the influence of these mon-soon conditions that generally pleasant weather prevails over most of the area.

Maritime tropical air is usually observed along the coast of China and over the Japanese Islands during the summer. In structure it is almost iden-tical to the mT air observed off the east coast of North America. The weather conditions found in this air are similar to those of its North American counterpart.

Equatorial air is observed over southeastern Asia. During the summer all of India and Burma are under the influence of E air, because of the summer monsoon circulation. In the wintertime, when offshore winds prevail, E air is not found over the land masses but is found some distance offshore.

Equatorial air is an extremely warm and moist air mass. It has great vertical depth, often extending beyond 20,000 feet in height. This en-tire column is unstable, and any slight lifting or small amount of surface heating tends to release the instability and produce showers and squalls. The equatorial air observed over India and Burma is almost identical in structure with E air found all along the equatorial zone over the

Figure 4-1-19.Properties of significant air masses over North America from the standpoint of flying(A) Winter; (B) Summer.

entire Earth. Unmodified equatorial air is ob-served over India and Burma during the summer monsoon. 

The weather conditions during the summer monsoon consist of cloudy weather with almost continuous rain and widespread shower activity. High temperatures and high humidities further add to the discomfort.

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