Monsoon

The monsoons of China and Japan are strongly affected by the huge land mass of Siberia. During the winter, the interior of Siberia becomes extremely cold. Cold air is dense, so a cold area of high pressure forms, where the air sinks from aloft. When it reaches the surface, the air spreads outward in all directions. The result is a dry winter monsoon that blows from the north through south China and southeast Asia. The same circulation affects northern China, Japan and Taiwan, where the prevailing wind is from the northwest. Although originally dry, the northwest winds pass over the sea and pick up moisture. When the winds arrive at the islands of Japan and Taiwan, they are forced up over the land. As a result, the western slopes of these islands experience a rainy winter monsoon.

During the summer, strong heating in the interior of Siberia sets up the summer circulation, giving south China, Indonesia, and southeast Asia humid southerly winds from the equator. Japan experiences winds from the south or southeast, which bring in moisture from the north Pacific Ocean.