Effect of changing tropical easterly jet, low level jet and quasi‐biennial oscillation phases on Indian summer monsoon

Abstract

Using the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis wind and homogeneous Indian summer monsoon (ISM) rainfall data during June, July, August and September (JJAS) for the period of 1953–2012, a long-term trend has been extracted in the tropical easterly jet (TEJ) and lower level jet (Somali jet/LLJ) along with the rainfall trend over Indian region using empirical mode decomposition (EMD) technique. The zonal wind speed at 100 hPa shows an increasing trend, while a decreasing trend is observed at 850 hPa. The quasi-biennial oscillation (QBO) phases, i.e. west and east phase, show a clear difference in wind anomalies at 100 and 850 hPa. A good (bad) monsoon year during the west (east) phase is confirmed on the basis of wind anomalies, velocity potential and divergent wind.