The Empirical Influences of Tibetan Plateau Soil Moisture on South Asian Monsoon Onset

Abstract

The South Asian High (SAH) location and intensity are linked with the Tibetan Plateau (TP) and Yangtze River basin latent heating. The existing feedbacks of SAH variability is rarely linked with TP soil moisture regulated energy fluxes. In this study, remotely sensed soil moisture and global atmospheric reanalysis products are used to quantify the relationship between the TP spring (April, May, June) soil moisture with SAH and South Asian (SA) monsoon onset during 1988–2008. The diagnostic analysis infers that the SAH exhibits a significant correlation (R ≥ 0.90) with TP spring soil moisture and monsoon onset indices (R≥ -0.56−-0.61). During the early and late monsoon onset, a significant anomalous soil moisture regime influenced the surface energy fluxes, which affected the vertical diabatic heating profile. The diabatic heating profile affects the TP ascending motion and SAH intensity, which leads to regional monsoon circulation changes and onset. An asymmetric SAH movement in the upper troposphere appears before the early and late monsoon onset composites and drives the lower tropospheric westerlies/easterlies winds towards the continental SA. The wind shear and transition from prevailing easterlies into westerlies during the pre-onset, onset, and post-onset pentad results in strong/weak ascent in the Bay of Bengal and advances into continental regions. The onset- mechanism further suggested intensified/weaker westerlies/easterlies during early/late onset composites. The SAH intensity and movement are linked with TP soil moisture, which exhibits teleconnections with the regional circulation pattern. A detailed model experiment will be conducted to verify the influence of soil moisture as a driver of energy fluxes and SA monsoon onset.