Effect of Sub-seasonal Tropical Oscillations on Extreme Weather over Indian Subcontinent

Extreme events over the tropics are known to be modulated by zonally propagating quasi-periodic intraseasonal oscillations like Madden - Julian oscillations and convectively coupled equatorial waves. Developing countries like India have high vulnerability to these events. The effect of these waves on the extreme events like, extreme precipitation and heat waves over Indian region is examined. It is shown that the phases of these waves significantly affect different extreme events over the country. However, the effect is highly dependent on the type of the oscillation and also regionally varying within the country. Frequency of extreme precipitations events (heat waves) is maximum during wet (dry) phases and minimum during dry (wet) phases. However the intensity of precipitation does not vary much from phase to phase. But the dry phase of Rossby waves increase both frequency and intensity of heat waves along with duration of heat waves. The results show that the westward propagating equatorial Rossby waves play a major role in modulating both precipitation extremes and heat waves over this region.The next prominent wave in modulating these events is Madden – Julian oscillation. These oscillations are shown to have significant effect in increasing the frequency of extreme rainfall as well as heat waves, but the effect is regionally varying. A quantitative estimation of the effect of these waves is explored along with the dynamical role played by these oscillations