Weather Wise

INDIA is awaiting with some anxiety the arrival of the summer monsoon rains. For the past few weeks, the plains in the north of the country have been sweltering in dry, 45C heat and dozens of people have died. As water and electricity supplies failed, the authorities have been roundly criticised for their failure to cope with the intemperate temperatures.

Fortunately, local meteorologists have predicted a normal monsoon this year, despite the meddling and disruptive influence of El Nino, which has thrown so much of the weather in the south-Asian region out of kilter.

The word monsoon is derived from the Arabic mausim, meaning "season". A monsoon is the large-scale seasonal reversal of the prevailing wind regime - usually involving a change in the direction of the dominant airflow of at least 120, causing distinct dry and wet seasons.

The most extreme monsoons are experienced in a region stretching from the Sudan and Tanzania, across the Indian Ocean to southern Arabia, over the Indian sub-continent, the countries of South-east Asia and China's seaboard. Unlike the West African monsoon, which is limited to the tropical zone, the Asian monsoon can extend far to the north, dumping huge amounts of snow onto the Himalayas and pushing even into the Tibetan plateau and Manchuria.

The causes of monsoonshave been much debated, and include the north and south migrations of the jet streams over the tropics. The moist air masses that lead to India's summer rains can originate from as far away as the Mediterranean and even the Atlantic.

But, to the farmers of India and Bangladesh, who look to the skies for their survival, the only question of any importance is when the rain will fall.