The Indian summer monsoon rainfall (ISMR) is closely linked with the food grain production and economic growth of India. It is about one hundred years since the importance of ISMR prediction was first recognised, after the 1899 famine that was caused by monsoon failure. Since then, several landmarks have been achieved in identifying the cause of monsoon failure. The Pacific El Nino has been identified as the most dominant factor. However, in recent time the El Nino-monsoon relation is reportedly weak. Other climate variability like the Indian Ocean dipole is shown to have more influence on ISMR.

However, the most recent failure of the ISMR in 2002 has puzzled the climate research community. In 2002, there was a weak El Nino in Pacific but ISMR was only ~78% of the climatological value. This was one of the most prominent event which was not envisaged by the major climate prediction systems around the world. Incidentally, we found that these prediction systems do not account for the effects of short-lived atmospheric constituents such as the aerosols, biomass burning products. This could be one of the major drawbacks of climate models and analyses as we found in the present study.

It is observed that the sea surface temperature of Arabian Sea (western Indian Ocean) in 2002 was colder than the climalogical mean or the 2003 excess ISMR year. We show that during the negative Indian Ocean dipole phase of 2002 wetter (drier) condition that prevails over Indonesia (eastern Africa) region, leads to the higher tropospheric column of ozone/aerosol over the western Indian Ocean and Arabian Sea. Further analysis of derived aerosol parameters indicate that the growth of cloud particle is inhibited by the presence of biomass burning emission such as smoke and transformed aerosol particles. Thus, we believe the changes in regional atmospheric composition, radiation balance and dynamical condition jointly dictate the success and failure of the ISMR.