explain the season of RETREATING MONSOON and ADVANCING MONSOON in brief and in easy language .
- Advancing Monsoon- A phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall which is attributed to the variations in temperature and pressure gradient. That causes its wet and dry spells. These breaks in monsoon are related to the movement of the monsoon trough. For various reasons, the trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall. When the axis of the monsoon trough lies over the plains, rainfall is good in these parts. On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains, and widespread rain occur in the mountainous catchment areas of the Himalayan rivers . The depressions follow the axis of the “monsoon trough of low pressure”. Thus, the variations in temperature and pressure causes irregularity in its arrival and retreat.
- Retreating Monsoon-The monsoon system refers to the seasonal reversal of the direction of winds. During the moths of May and June, the winds advance from the south-west direction to the north-east direction. These moisture laden winds arrive from the Arabian Sea are represent the advancing monsoon. The pattern is reversed around mid-September or the time of autumnal equinox with a change in the pressure conditions caused by the shifting of direct sunrays towards equator from the Tropic of Cancer. This causes a cooling of the subcontinental landmass. The differential heating of the land and the adjoining water bodies like Bay of Bengal and Indian Ocean, which still retain a high temperature cause an exaggerated difference in pressure conditions. High pressure areas are formed over the landmass. The wind direction is reversed and moves in the south-east direction towards the Bay of Bengal. The dry off shore wind carries moisture form the Bay of Bengal and causes precipitation parts of Andhra Pradesh and Tamil Nadu during winter. This entire phenomenon is known as retreating monsoon.