Contrasting features of wave number one during northern summer monsoon seasons of 1997 and 2002

Abstract

Temporal and spatial variations of the energetics of the lower tropospheric zonal wave number one are compared for monsoon 2002 (a recent drought year) and monsoon 1997 (a normal monsoon year).  Fourier technique is used to calculate momentum transport, kinetic energy and wave to wave interaction. Daily global grid point NCEP wind (u & v) data at 850 hPa for 153 days (1 May to 30 September) are considered.

                Daily and weekly variations of the energetics of wave number one indicate that as long as the momentum transport or kinetic energy of wave number one around 10° N  is strong, the rainfall is better and vice-versa. The  amplitude of wave number one was almost half during 2002 as compared to that of during 1997,  which resulted into less transport of momentum and meager supply of kinetic energy throughout the monsoon season of 2002. The significant release of kinetic energy by wave number one may have played a vital role in triggering five intense systems during 1997 whereas the  weak supply of kinetic energy  may have failed to trigger a single system during monsoon 2002.