<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> <P> A positive IOD index often negates the effect of ENSO, resulting in increased monsoon rains in years such as 1983, 1994, and 1997 . Further, the two poles of the IOD--the eastern pole (around Indonesia) and the western pole (off the African coast)--independently and cumulatively affect the quantity of monsoon rains . </P> <P> As with ENSO, the atmospheric component of the IOD was later discovered and the cumulative phenomenon named Equatorial Indian Ocean oscillation (EQUINOO). When EQUINOO effects are factored in, certain failed forecasts, like the acute drought of 2002, can be further accounted for . The relationship between extremes of the Indian summer monsoon rainfall, along with ENSO and EQUINOO, have been studied, and models to better predict the quantity of monsoon rains have been statistically derived . </P> <P> Since 1950s, the South Asian summer monsoon underwent a gradual decline, with a reduction of up to 10% over central India . This is primarily due to a weakening monsoon circulation as a result of the rapid warming in the Indian Ocean, and changes in land use and land cover . Since the strength of the monsoon is partially dependent on the temperature difference between the ocean and the land, higher ocean temperatures in the Indian Ocean have weakened the moisture bearing winds from the ocean to the land . The reduction in the summer monsoon rainfall have grave consequences over central India because at least 60% of the agriculture in this region is still largely rain - fed . </P>

How do monsoon winds impact climate and seasonal changes in southeast asia