EL NINO EFFECT AND INDIAN MONSOON RAINS
Last year and also in 2015 Indian Met Dept had forecast that monsoon rains would be affected appreciably by EL NINO . The 2014 monsoon was appreciably deficient and this year after good rains in June and July it is expected that rains will not be as deficient as last year. It may be noted that harvests have got a minimum asking level of rainfall. Less than 10 year average rainfall does not have much indication of this. It appears that fortunately rains in both these years virtually satisfied or is going to satisfy this asking rate although it appeared that RBI and other govt, bodies became a bit over perturbed by IMD forecasts to adjust their arithmetic. But what is this fearsome EL NINO?
The largest waters on the earth are those of the Pacific Ocean. Its eastern equatorial (or tropical) area (approximately between the International Date Line and 120 degrees West) witness two unique syndromes called EL NINO (the small boy)and LA NINA (the little girl) which when they occur, disturb the regularity of global atmospheric behaviour in various ways. Incidentally, equatorial region of the earth receives the fiercest sun generating most of the strong turbulence in its waters and the atmosphere.
EL NINO( the small boy): This syndrome signifies undue warming (0.5 to 1.5 degC temperature differential over normal ) of the surface over eastern equatorial Pacific ocean for a prolonged period of several months. This extra warmth in turn warms up the wind over the warmer ocean surface over a vast area causing additional turbulence with unusual showers and thunder storm over warm waters . This disturbs the seasonal behaviour of the atmosphere, in turn disturbing regularity and quantum of rains , atmospheric temperatures and wind pattern as the trade winds that flow along equatorial pacific from east to west tend to weaken at places causing less rains away from the formation of warm surface waters. Conversely warm waters tend to travel in the opposite direction to the trade winds to cause more showers where the go. A term ENSO ( EL NINO & SOUTHERN OSCILLATIONS) is often used to cover this composite effect of ocean surface and the wind under EL NINO condition.
But why we suffer in India when our distance From the Pacific waters is half the global periphery? The answer lies in the fact that the warm ocean surface during EL NINO condition travels hundreds of kms eastward toward the far east Pacific bringing about strong thunderstorm and rains where they go. The winds that move in the opposite direction ( natural direction of wind is from east to west due to rotation of the earth) induce the surface atmosphere with weakening of rains and storm . More than physical movement of the winds this inducement is effected by telecommunication via waves through the atmosphere effecting a global climatic discord. Thus equatorial Indian ocean which influences generation of our monsoon trade winds also get affected and we get less rains and storms.
LA NINA (the little girl): This phenomenon is just opposite to EL NINO and occurs with drop in the surface temperature of the equatorial Pacific waters to the same extent. Its effect is roughly the opposite of EL NINO. It has a cooling effect as the surface waters travel east ward. But since for us its effect is inconsequential there may be no need to dilate on this.
Dibyendu Sekhar Kumar