WINDS AND RAINFALL
4. In the Bay of Bengal furious cyclones or hurricanes are sometimes
»xperienced ; while in the Chinese Seas similar winds are known as
byphoons. These are systems of low atmospheric pressure and small
area, in which the pressure decreases rapidly towards the interior, and
;owards which winds blow violently in all direcetions. "This inward motion,
being deflected on account of the earth’s Totation, creates a sort of whirl,
which, in the northern hemisphere, moves in the direction opposite to
“hat of the hands of a clock. Heavy rainfall accompanies these storms,
as the air is always rising, and much damage to life and property is often
vrought by their fury.
The areas of deficient rainfall in Asia are: (1) Distriets
which are so far inland, or so shut in by mountains, that the winds from
the sea do not reach them, or have precipitated their moisture on their
way. Such, for example, are the deserts of Gobi and West Turkistan.
‚2) Areas in the belt of the dry north-east trade wind, which do not
receive ocean winds in summer, such as the desert of Thar in India, and
‘he Iranian and Arabian deserts. (3) The northern regions, where the
sold hinders evaporation, and hence limits the rainfall. What moisture
is precipitated here falls partly in the form of Snow, and this is deep in
winter ; but about 10 inches of snow are, in volume of moisture, only
2quivalent to 1 inch of rain.
CLIMATE AND VEGETATION.
Vegetation depends chiefly on elimate ; and from what has gone before
we see Asia can be divided into the following climatic areas. each of
which will have its characteristie vegetation :
1. The frigid region, or tundras, in the north, practically in-
oluding the land within the Aretic Circle. Here the intense cold reduces
vegetation to mosses, bushes, and stunted trees ; while much of the
island of Novaya Zemlia is covered with an ice-sheet, Some of the few
plants found in the Arctic regions occur also in other parts of Asia on
high mountains (see p. 27).
2. The cool temperate region south of the above area,
where forests predominate. This includes the whole of Eastern Siberia,
and Western Siberia to about latitude 57° The most common trees are