Effect of tropical sub-seasonal variability on heatwaves over India

Abstract

One of the important consequences of changing climate is the increase in temperature extremes and heat stress over many regions of the world. Understanding the various factors that modulate these events on different time scales is of utmost importance due to their great societal relevance. For example, understanding and prediction on sub-seasonal time scales is crucial for reducing losses due to extremes and diligent management of limited resources. In this study, the effect of tropical intraseasonal oscillations like convectively coupled equatorial waves (CCEWs) such as equatorial Rossby wave (ER), Kelvin wave, mixed Rossby gravity waves and the Madden and Julian Oscillations (MJO) in modulating heatwaves occurrence over India is explored. We find that these oscillations significantly modulate extreme heat events. The extent of the modulation is also found to be highly dependent on the location, type and phase of these waves. The maximum effect is observed in case of ER with positive phase (defined as high outgoing longwave radiation phase) enhancing the frequency of the events by almost twice the normal values, and supporting long duration and more intense heatwaves while the opposite phase totally suppresses the heatwave events. The effect of MJO is region dependent with positive (negative) phase increasing (decreasing) the heatwave frequency over South and Eastern (North-western) parts of the country. Kelvin and MT waves are also found to have lesser but significant effect on heatwaves, and mostly reduces the occurrence of heatwaves. Overall, the study shoes that the ER wave has the most significant effect on the frequency and duration of heatwaves over the study region. � 2020 Royal Meteorological Society