Assessment of extreme seasonal rainfall over India in current seasonal coupled models during the recent period

The present study analyses the performance of recent seasonal prediction coupled models in simulate the seasonal extremes (June through September) over the India using February and May initializations (hear after FEBIC & MAYIC) for a period of 1981-2018. All the models show significant seasonal dry bias over the northern and western coast of Indian regions (associated with northerly wind bias at lower troposphere), whereas strong wet bias over the southeastern India which is associated with cyclonic circulation (at 850 hPa) over the central Bay of Bengal. CFSv2 hindcasts has more dry bias over India for FEBIC due to strong northerly wind bias over the Northern India and strong cyclonic circulation over the North West Pacific, whereas, that dry bias is reduced significantly over the Northern Indian region in all the models except GEM-NEMO in MAYIC. CFSv2 reproduces the orographic rainfall over the west coast and northeastern parts of India in both leads. The models are not able to reproduced the extreme years that are associated with El Nino, Indian Ocean Dipole and Atlantic Nino boundary forcing (BF), while the observed normal years which co-occur with these BF are represented as excess years in the models. Categorical skill scores suggest that, all the models can capture the normal years only as similar to observations whereas deficient and excess years have more false alarms mainly due to the misrepresentation of ascending and descending branches of the Walker circulation over the tropics during the extreme years.