Mid-winter Stratospheric Warming Effects on Tropical Convection over the Indian Sector: Case Studies

Abstract

The present study investigates the impact of northern mid-winter major stratospheric warming on tropical convection over the Indian region by examining the five Mid-winter Major Stratospheric Warming (MSW) events 2003/04, 2005/06, 2008/09, 2012/13, and 2018/19. The dynamical variables like temperature, wind components, and Outgoing Longwave Radiation are utilized from ECMWF ERA-Interim Reanalysis and NOAA site. Eliassen Palm (E-P) flux is used to visualize the upward and equator-ward propagation of extratropical Planetary Waves (PWs) from the lower atmosphere and their reach to the tropical region. The dominance of extratropical PW forcing from high to low latitudes is seen in all mid-winter cases. Further, the transfer of PW energy to low latitudes modifies the convection pattern over the Indian region. The author found depleted convection in the latitude band -15-20oN for the MSW 2003/04 and 2018/19, with frequent changes seen during MSW 2012/13 and 2005/06. On the other hand, the MSW 2008/09 show enhanced convection in the entire latitude band 20oS-20oN. This work suggests that the modification of OLR depends on the PW energy, onset time, peak temperature, and wind-reversed state during MSW.