INTRODUCTION

The climate of India is essentially sub tropical monsoonic. The word ‘monsoon’ has been derived from the Arabic word ‘mausim’ which means ‘season’. Originally, the word ‘monsoon’ was used by Arab navigators several centuries ago, to describe a system of seasonal reversal of winds along the shores of the Indian Ocean, especially over the Arabian Sea, in which the winds blow from the south-west to north-east during the summer season and from the north-east to south-west during the winter season. In other words, monsoons are periodic (seasonal) winds in which there is a complete reversal of the wind direction after every six months.

In the opinion of Chang-Chia-Cheng: “Monsoon is a flow pattern of the general atmospheric circulation over a wide geographical area, in which there are clearly dominant winds in one direction in every part of the region concerned, but in which this prevailing direction of wind is reversed or almost reversed from winter to summer, and from summer to winter.”

Monsoons are especially prominent within the tropics on the eastern sides of the great landmass, but in Asia, it also occurs outside the tropics in China, Korea, andjapan, and may be observed up to 60° north. South-East Asia, especially the subcontinent of India, however, is a typical example of a monsoon region. Other areas which experience similar but less pronounced seasonal changes of wind direction include south eastern USA, the Caribbean Islands, Madagascar, East Africa, the Guinea coast of West Africa, South east Asia, Philippines, south eastern China, South Korea, and North Australia (Fig. 4.1).