On the Asymmetry of Indian Summer Monsoon Predictability During Warm and Cold ENSO Events

Conventional wisdom has been that Indian monsoon variability is smaller during El Nino Southern Oscillation (ENSO) years compared to for the ENSO neutral years. This has been argued for the well-known monsoon-ENSO relationship, also exploited for its prediction. However, we find that the monsoon variability during neutral and El Nino years is similar and higher than for La Nina years which are contrary to conventional wisdom. Furthermore, the difference is largely observed in the distribution of variance in the intraseasonal time periods (~30-60 days). Analysis of tropical Ocean and Atmospheric fields suggests that during El Nino years the tropospheric temperature is warmer and conducive for enhanced Madden-Julian Oscillation activity resulting in increased variability of the monsoon, and vice-versa during La Nina years. In addition the variability of tropical Pacific SSTs during El Nino years is higher than during La Nina years. Understanding and modeling this teleconnection can be important for improving the skill of monsoon forecasts. This could also shed light on the tropical wide predictability of rainfall during warm and cold ENSO events. We provide evidence of this hypothesis from model experiments of CCSM and GFS models.