Use of large-scale atmospheric energetics for understanding the dynamics of contrasting Indian summer monsoon rainfall in different years

An attempt has been made to understand the dynamics of contrasting Indian summer monsoon rainfall (ISMR) in different years during 1979-2017, from large-scale atmospheric energetics aspects. Daily values of eddy and zonal available potential energy (APE), their generation, eddy and zonal kinetic energy (KE), conversions of zonal KE and eddy APE to eddy KE, and conversions of zonal APE to zonal KE and eddy APE were computed over the region bounded by 65 degrees E-95 degrees E and 5 degrees N-35 degrees N during the period 1 May to 30 September for 39years (1979-2017), using daily ECMWF reanalyzed atmospheric data at 0.125 degrees x0.125 degrees resolution (3 components of wind and temperature). ISMR was classified into three categories, viz., deficient and below normal, normal and above normal and excess. The daily anomaly of these energetics parameters in each of these years was computed using jackknife method and then the composite of the daily anomalies of these parameters constructed for the years with the above-mentioned three categories of ISMR. The following salient features emerge from this study: Analysis of composite anomaly shows that in case of excess and above normal (below normal and deficient) ISMR, C(A(Z), K-Z) was less (more) than normal. In case of excess and above normal (below normal and deficient) ISMR, C(A(E), K-E) was more (less) than normal. Broadly, C(A(Z), A(E)) was more than normal in the years with deficient and below normal ISMR, whereas it was less than normal for years with excess and above normal ISMR. Broadly, G(A(Z)) was below normal for the years with above normal and excess ISMR, whereas it was above normal for the years with below normal and deficient ISMR. Total kinetic energy and total conversion to eddy kinetic energy was above normal for the years with above normal and excess ISMR.