The Arabian Sea branch strikes the elevated Western Ghats of India at almost right angles

The Arabian Sea branch strikes the elevated Western Ghats of India at almost right angles. The windward slopes of Western Ghats receive heavy orographic precipitation. However, the westerly current from the Arabian Sea continues its journey across the Indian Peninsula, but the amount of rainfall on the leeward side goes on diminishing with increasing distance from the sea coast.

The Western Ghats have 100-250 cm of rainfall on their windward slopes, while there is a well-marked rain-shadow to the leeward. At Mahabaleshwar the rainfall amounts to 650 cm, while at Pachgani, only 16 km to the east, the amount of rainfall is reduced to 170 cm.

The most characteristic feature of the distribution of rainfall on windward slope is that the amount of rains is heavier higher up the slopes. However, the heavy rains are confined in a narrow strip along the western slopes.

After crossing the Western Ghats the rain-bearing air currents descend the eastern slopes where they get warmed up adiabatically. This results in a pronounced rain shadow. Higher the mountains, larger are the rain shadow effect. Towards the north, where the Western Ghats are not very high, the difference in the amount of rainfall between the windward and leeward side is rather negligible.

A few air currents from the main Arabian Sea branch are diverted northward towards Cutch and Thar Desert. These air currents continue their onward march up to Kashmir. In the absence of any barrier across their path, these currents do not yield precipitation in Rajasthan, which practically remains dry.

The Aravallis being parallel to the direction of these monsoon currents fail to block their passage and lift them. That is why Rajasthan remains a desert. Here, it may be pointed out that the decreasing amount of rainfall from the Gulf of Cambay northward can be explained by two factors: (a) trajectory of air currents, and (b) dryness of the air mass of Sind.

An east to west line drawn near Karachi in Pakistan practically marks the limit of monsoon rainfall. To the north of the line, the winds are dry and stable, whereas to the south the winds travelling over the Arabian Sea develop a high potential for heavy precipitation.

The monsoon currents heading towards Rajasthan are rather shallow and are superimposed by stable anticyclonic air.

There is, therefore, little possibility of their uplift and consequent precipitation. In addition, the hot and dry continental air masses from the west and northwest are drawn towards the thermal low developed in this region. Because of their descent, such conditions as are unfavourable for precipitation are produced here.

Some of the air currents from the Arabian Sea branch manage to proceed towards Chhota Nagpur plateau through the Narbada and Tapti gaps. These air currents ultimately unite with the Bay of Bengal branch.