Impact of Atmospheric Moisture Transport on Interannual and Intraseasonal Variations of the Indian Summer Monsoon

The large-scale disturbances that primarily originate over the oceans and mid-latitudes regions result into variability in Indian Summer Monsoon Rainfall (ISMR) at various timescale viz. intraseasonal, interannual etc.. For correct modeling and prediction of ISMR, an understanding of the causes and impact of variability at different time scale and their interaction with each other is important. The impact of these large­­-scale disturbances can be studied by identifying the moisture transport from different sources to India during summer monsoon. Here, we address two important question regarding the variability of ISMR; firstly how and to what extent atmospheric moisture transport variability from different oceanic sources are linked with interannual and intraseasonal variability?; and Secondly the link between the intraseasonal and interannual variability through atmospheric moisture transport. The variability in atmospheric moisture transport from major evaporative sources which contribute to ISMR is studied. We analyzed the atmospheric moisture transport from different oceanic sources to ISMR. The analysis is performed with ECMWF-ERA-interim reanalysis data using Lagrangian trajectory approach at daily timescale and at spatial resolution of 0.75° x 0.75°. The interannual variability of Indian monsoon originates from the ocean-atmosphere interactions, which vary at a range of scales. We observe that the anomaly pattern of moisture contributions from the major oceanic sources, Western Indian Ocean and Central Indian Ocean, during strong and weak monsoon years are very similar to the MISO and provide the possible linkage between the two scales of variability (intra-seasonal and interannual). Our findings also highlight that the sink for the moisture evaporated from the major moisture sources have large amount of spatial variability during strong and weak rainfall years. The novelty of present work lies in understanding the role of different evaporative sources of the Indian Ocean, in different scales of ISMR variability.