The Northeast Winter Monsoon over the Indian Subcontinent and Southeast Asia: Evolution, Interannual Variability, and Model Simulations

Abstract

The northeast monsoon (NEM) brings the bulk of annual rainfall to southeastern peninsular India, Sri Lanka, and the neighboring Southeast Asian countries. This October–December monsoon is referred to as the winter monsoon in this region. In contrast, the southwest summer monsoon brings bountiful rainfall to the Indo-Gangetic Plain. The winter monsoon region is objectively demarcated from analysis of the timing of peak monthly rainfall. Because of the region’s complex terrain, in situ precipitation datasets are assessed using high-spatiotemporal-resolution Tropical Rainfall Measuring Mission (TRMM) rainfall estimates, prior to their use in monsoon evolution, variability, and trend analyses. The Global Precipitation Climatology Center’s in situ analysis showed the least bias from TRMM. El Niño–Southern Oscillation’s (ENSO) impact on NEM rainfall is shown to be significant, leading to stronger NEM rainfall over southeastern peninsular India and Sri Lanka but diminished rainfall over Thailand, Vietnam, and the Philippines. The impact varies subseasonally, being weak in October and strong in November. The positive anomalies over peninsular India are generated by anomalous anticyclonic flow centered over the Bay of Bengal, which is forced by an El Niño–related reduction in deep convection over the Maritime Continent. The historical twentieth-century climate simulations informing the Intergovernmental Panel on Climate Change’s Fifth Assessment (IPCC-AR5) show varied deficiencies in the NEM rainfall distribution and a markedly weaker (and often unrealistic) ENSO–NEM rainfall relationship.

The Full Extent of El Niño's Precipitation Influence on the United States and the Americas: The Suboptimality of the Niño 3.4 SST Index

“…And in the shoulder seasons of winter, i.e., preceding fall and subsequent spring is it even adequately characterized? Answers are sought from analyses of century-long (1901-2016) SST and precipitation records as realistic representations of regional hydroclimate variability still elude climate system models, at least, of the IPCC-AR5 genre (Sengupta & Nigam, 2019).…”

The impact of varying seasonal lengths of the rainy seasons of India on its teleconnections with tropical sea surface temperatures

“…Therefore, the teleconnections exhibited by the winter anomalies over northern India in this paper is consistent with such an interpretation. In this study, a robust negative correlation is shown between the winter rainfall anomalies over southeastern India with the tropical Pacific, which at the outset seems contrary to previous studies (Rajeevan et al ., ; Sengupta and Nigam, ). However, the earlier studies have reported comparatively much weaker correlations and have used a different season for IWM (e.g., October–November–December).…”

“…On the other hand, despite the strong variability of the Indian Winter Monsoon (IWM) rainfall and its relatively strong teleconnection with ENSO (Ramaswamy, 1972;Zubair and Ropelewski, 2006;Kumar et al, 2007;Rajeevan et al, 2012;Dimri et al, 2016;Misra and Bhardwaj, 2019;Sengupta and Nigam, 2019) the models continue to display poor fidelity of the IWM (Rajeevan et al, 2012;Sengupta and Nigam, 2019).…”

On the simulation of northeast monsoon rainfall over southern peninsular India in CMIP5 models

“…An anomalous anticyclonic circulation over the Bay of Bengal is observed in the wind regression pattern. This anticyclone is forced by the reduction of deep convection over the Maritime continent which is related to El Nino (Sengupta et al, 2019). Due to this anticyclonic circulation, the number of tropical cyclones forms over Bay of Bengal is below (above) normal during El Nino year (La Nina year) (Girshkumar et al2015).…”