Understanding the Revival of the Indian Summer Monsoon after Breaks

Understanding the Revival of the Indian Summer Monsoon after Breaks

Govardhan Dandu¹, Vadlamudi Brahmananda Rao² and Karumuri Ashok¹

1. University Centre for Earth and Space Sciences, University of Hyderabad, Hyderabad.

2. Emeritus professor, INPE, Brazil.

In this paper, we suggest a dynamical mechanism involved in the revival of summer monsoon after breaks. In this context, we carry out a diagnostic analysis using the datasets from National Centres for Environmental Prediction reanalysis-2 for the period 1979-2007 to identify a robust mechanism that typifies breaks and subsequent revival of monsoon. We find that during the peak of significant breaks, an anomalous southward shift of subtropical westerly jet stream, which is invariably accompanied by anomalous northward shift of a stronger-than-normal easterly jet. These major changes during a break facilitate an instability mechanism, which apparently leads to formation of a synoptic disturbance. Formation of such a disturbance is often critical to the subsequent revival of summer monsoon. Our computations of energetics and correlation analysis suggest an increase in the eddy kinetic energy at the expense of the mean kinetic energy during the breaks, in agreement with the formation of the synoptic disturbance with monsoon trough deepening. This demonstrates that barotropic instability in the presence of a monsoon basic flow is the primary physical mechanism that controls the summer monsoon breaks and subsequent revival of the monsoon.

In the below image: CMKE: Rate of Conversion Mean Kinetic Energy Values.