Predictability of seasonal mean monsoon

The influence of slowly-varying boundary forces, such as sea surface temperature, soil moisture and snow, on the variability of the atmosphere provides hope for long-range predictability of climate models. This study shows that the variability of the monsoon consists of a combination of large-scale persistent seasonal mean component and intraseasonal variability of different time scales. By performing multi-channel singular spectrum analysis (MSSA) of daily rainfall, low-pressure systems, outgoing long-wave radiation and winds, two intraseasonal oscillatory modes have been identified and shown to correspond to the active and break phases of the monsoon. These two intraseasonal modes, however, do not contribute much to the seasonal mean rainfall. Three other components of the MSSA are identified as the contributors to the seasonal mean rainfall, possibly arising from the influence of slowly-varying boundary forces. The relation between the components with persistent seasonal signature in rainfall and circulation variables and the SST of the Indian and Pacific Oceans is discussed.