Despite the overall unity accorded by the monsoon, there are visible regional variations in climatic conditions within India. Regardless of the moderating influences of the Himalayas in the north and the sea in the south, variations do exist in temperature, humidity and precipitation. For example, in summer, some parts of the Rajasthan desert, in north-western India, record temperatures of 50°C, while it may be around 20°C in Pahalgam in Jammu and Kashmir, in the north of the country. On a winter night, the temperature at Drass in Jammu and Kashmir may be as low as minus 45°C, while Thiruvananthapuram may have a temperature of 22°C. In general, coastal areas experience less contrasts in temperature conditions. Seasonal contrasts are more in the interior of the country.
Another case in point is precipitation. While precipitation is mostly in the form of snowfall in the upper parts of the Himalayas, it rains over the rest of the country. The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan. Most parts of the country receive rainfall from June to September, but some parts like the Tamil Nadu coast get most of their rain during October and November.
Discuss the mechanism of monsoons.
During summer, a low-pressure area develops over interior Asia as well as over north and north-western India. At the same time, there is a high-pressure system over the southern Indian Ocean. Winds move from a high-pressure area to a low-pressure area. As a result, the low-pressure system attracts the southeast trade winds of the southern hemisphere. On crossing the equator, these trade winds—due to the Coriolis force—turn right towards the low-pressure areas over the Indian subcontinent. After crossing the equator, these winds start blowing in a south-westerly direction, and enter the Indian peninsula as the southwest