Figure 12. A schematic representation of the east-west
Walker Circulation of the tropics. In normal seasons air rises over the
warm western Pacific and flows eastward in the upper troposphere to subside
in the eastern Pacific high pressure system and then flows westward (i.e.
from high to low pressure) in the surface layers across the tropical Pacific.
Weaker cells also exist over the Indian and Atlantic Oceans. In El Niño
years, this circulation is weakened, the central and eastern Pacific Ocean
warms and the main area of ascent moves to the central Pacific.
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