Modulation of ISOs by land-atmosphere feedback and contribution to the interannual variability of Indian summer monsoon

A mechanism of internal variability of Indian summer monsoon through the modulation of intraseasonal oscillation (ISO) by land-atmosphere feedback is proposed. It is shown that a strong break (active) phase is followed by a strong active (break) phase. Evidence of feedback between surface soil moisture and ISOs is seen in the soil moisture data from GSWP-2 and rainfall data from observations. Using internal simulations by a regional climate model (RCM), it is shown that internally generated anomalous soil moisture interacts with the following ISO and generates interannual variability. The feedback appears to be inherent to the monsoon system and a part of it acts through the intraseasonal varying memory of soil moisture. Soil moisture and ISO feedback may have also important implication in terms of improved initial soil moisture condition in dynamical prediction model, which may in turn improve the monsoon rainfall forecast on intraseasonal timescale.