The role of surface air temperature over the east Asia on the early and late Indian Summer Monsoon Onset over Kerala

Devanil Choudhury,Wen Chen,Debashis Nath

doi:10.5194/egusphere-egu2020-3820

Abstract

&lt;p&gt;We investigated the physical mechanism for late Indian Summer Monsoon onset over Kerala&lt;br&gt;(MOK). 14 early and 9 late onset years are selected based on the criteria when the onset is 5 days or&lt;br&gt;more prior and after normal onset date (i.e 1 st June according to India Meteorological Department)&lt;br&gt;respectively. Then, we perform composite analyses of mean May monthly and daily evolution during&lt;br&gt;early and late onset years to examine the differences in monsoon circulation features prior to the MOK.&lt;br&gt;We find that advection of Surface Air Temperature (SAT) from the northern to the southern China and&lt;br&gt;the eastern Tibetan Plateau (TP) plays an important role to modulate the MOK processes. In the late&lt;br&gt;onset years, more low-level jet (LLJ) from the Bay of Bengal (BOB) divert towards the east Asia before&lt;br&gt;the onset, which is due to an extension of the low sea level pressure and high SAT over the east Asia&lt;br&gt;(eastern TP, east-central China). This strengthens the low-level convergence and upper level divergence&lt;br&gt;over the eastern TP and southern China. As a result, a significant amount of moisture from the BOB&lt;br&gt;is transported towards the eastern TP and southern China. Thereby, a comparatively weaker LLJ and&lt;br&gt;deficit low-level moisture supply over the eastern BOB maintain the key roles in modulating the MOK&lt;br&gt;processes.&lt;/p&gt;

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