Understanding the underlying dynamics of the Indian summer monsoon (ISM) extremes such as severe droughts is key to improving seasonal prediction of the ISM rainfall. A large number of ISM droughts over the past century occurred unrelated to
external forcing like the El Niño–Southern Oscillation (ENSO). In this study, we challenge the perception that the 2009 ISM drought was driven by ENSO and show that it was caused by internally driven processes.

Reliable medium range prediction of monsoon weather is crucial for disaster preparedness. Weather in tropics, controlled by fast growing convective instabilities is, however, intrinsically less predictable than that in extra?tropics.

The concept of an interannually varying Indian summer monsoon season is introduced here, considering that the duration of the primary driving of the Indian monsoon - the large-scale meridional gradient of the deep tropospheric heat source - may vary from one year to another. Onset (withdrawal) is defined as the day when the tropospheric heat source shifts from south to north (north to south).

Against a backdrop of rising global surface temperature, the stability of the Indian monsoon rainfall over the past century has been a puzzle.

Being an integral effect of sub-seasonal rain spells over the season, the seasonal mean south Asian monsoon (SAM) rainfall could be affected by change in the length of the rainy season (LRS). An objective definition of the duration of the SAM season has, however, been lacking.