<P> El Niño is a warm ocean current originating along the coast of Peru that replaces the usual cold Humboldt Current . The warm surface water moving toward the coast of Peru with El Niño is pushed west by the trade winds, thereby raising the temperature of the southern Pacific Ocean . The reverse condition is known as La Niña . </P> <P> Southern oscillation, a phenomenon first observed by Sir Gilbert Thomas Walker, director general of observatories in India, refers to the seesaw relationship of atmospheric pressures between Tahiti and Darwin, Australia . Walker noticed that when pressure was high in Tahiti, it was low in Darwin, and vice versa . A Southern Oscillation Index (SOI), based on the pressure difference between Tahiti and Darwin, has been formulated by the Bureau of Meteorology (Australia) to measure the strength of the oscillation . Walker noticed that the quantity of rainfall in the Indian subcontinent was often negligible in years of high pressure over Darwin (and low pressure over Tahiti). Conversely, low pressure over Darwin bodes well for precipitation quantity in India . Thus, Walker established the relationship between southern oscillation and quantities of monsoon rains in India . </P> <P> Ultimately, the southern oscillation was found to be simply an atmospheric component of the El Niño / La Niña effect, which happens in the ocean . Therefore, in the context of the monsoon, the two together came to be known as the El Niño - Southern Oscillation (ENSO) effect . The effect is known to have a pronounced influence on the strength of the southwest monsoon over India, with the monsoon being weak (causing droughts) during El Niño years, while La Niña years bring particularly strong monsoons . </P> <P> Although the ENSO effect was statistically effective in explaining several past droughts in India, in recent decades, its relationship with the Indian monsoon seemed to weaken . For example, the strong ENSO of 1997 did not cause drought in India . However, it was later discovered that, just like ENSO in the Pacific Ocean, a similar seesaw ocean - atmosphere system in the Indian Ocean was also in play . This system was discovered in 1999 and named the Indian Ocean Dipole (IOD). An index to calculate it was also formulated . IOD develops in the equatorial region of the Indian Ocean from April to May and peaks in October . With a positive IOD, winds over the Indian Ocean blow from east to west . This makes the Arabian Sea (the western Indian Ocean near the African coast) much warmer and the eastern Indian Ocean around Indonesia colder and drier . In negative dipole years, the reverse happens, making Indonesia much warmer and rainier . </P>

Most of the india remains dry during northeast monsoon give reason