The seasonal reversal of winds and the associated rainfall. This word is derived from the

Arabic word “Mausim”. The annual oscillation in the apparent position of the Sun between

the Tropics of Cancer and Capricorn causes the annual oscillation in the position of the

thermal equator (region of maximum heating) on the Earth’s surface. This is associated

with the annual oscillation of temperature, pressure, wind, cloudiness, rain etc. This is the

cause of the monsoons. On the Earth’s surface, there are asymmetries of land and

Ocean. The differential heating of land and Ocean cause variations in the intensity of the

annual oscillation of the thermal equator and hence regional variations in the intensity of

monsoon. The southwesterly wind flow occurring over most parts of India and Indian

Seas gives rise to southwest monsoon over India from June to September

                                                 FACTS AND FIGURES

EI NINO

                          The oceanic atmospheric phenomenon wherein waters in the equatorial Pacific warm up abnormally due to weakening of trade winds is termed as El Nino.El Nino, means ‘little boy’ in Spanish. It is a weather system which re-emerges after a gap of about two to five years in the Pacific Ocean and its effects last for about 12 months on an average.

               El Nino leads to warming of sea surface temperatures, which in turn affects wind patterns and triggers both floods and droughts in different parts of the world.

                                            El NINO AND INDIAN MONSOON

                        This phenomenon affects rainfall in India during the Monsoon months. Trade winds normally blow westward from South America towards Asia during Indian monsoon months. Warming of the Pacific results in weakening of these winds. Moisture and the heat content thereby, gets limited and results in reduction and uneven distribution of rainfall across the Indian sub-continent.

LA NINA

                         La Nina means The Little Girl in Spanish. La Nina is also sometimes called “a cold event.”La Nina episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific. Global climate La Nina impacts tend to be opposite those of El Nino impacts.

                El Nino and La Nina are opposite phases of what is known as the El Nino-Southern Oscillation (ENSO) cycle.

CLOUDS

Clouds are aggregate of very small water droplets, ice crystals, or a mixture of both, with

its base above the earth’s surface. A classification is made in level – high, medium, or low – at which the various cloud genera are usually encountered.   In temperate regions the approximate limits are high, (16500 – 45000 ft); medium, 2­7 km (6500 –23000 ft); low, 0­2 km (0 – 6500 ft).

The high clouds are Cirrus (Ci), Cirrocumulus (Cc),Cirrostratus (Cs).

The medium clouds are Altocumulus (Ac), Altostratus (As) (the latter often extending higher) and Nimbostratus (Ns) (usually extending both higher and lower);

The low clouds are Stratocumulus (Sc), Stratus (St), Cumulus (Cu), and Cumulonimbus(Cb).