Out‐of‐phase relationships between convection over northwest India and warm pool region during the winter season

Abstract

ABSTRACT:In this paper, we investigate the effect of convection over warm pool region of Indonesia on northwest India winter precipitation (NWIWP) using an analysis of latest available observed climate data. The analysis is based on correlations and composites performed using India Meteorological Department (IMD) records of station data. We find that there is an out-of-phase relationship between convection over warm pool region and northwest India during the winter season. In particular, a positive precipitation anomaly over northwest India is typically found in correspondence to subdued convection over warm pool region. A physical mechanism for such effect is proposed, by which during excess years of NWIWP the tropical cooling over the warm pool region due to suppressed convection generates an upper-level convergence (cyclonic circulation) anomaly over south Asia which intensifies the westerly jet stream over Indian region. Also, the reduced convection over the warm pool may be due to reduced Madden-Julian oscillation (MJO) activities on the intra-seasonal timescale. The Rossby-gyre dynamics with the strong vertical and westward meridional tilts in the tropical baroclinic atmosphere forms cyclonic circulation anomalies at the upper troposphere due to a weak MJO which intensifies the westerly jet stream over the Indian region. The jet stream guides the western disturbances (WDs) and hence increases precipitation over northwest India. The seasonal persistence in migration of convective maximum from south Asia (foothills of the Himalayas) to Indonesia during the peak months of boreal summer to winter increases the seasonal predictability of NWIWP.

Increasing influence of ENSO and decreasing influence of AO/NAO in the recent decades over northwest India winter precipitation

“…The deep vertical structure of the tropical heating and cooling over equatorial Pacific and warm pool, respectively, gives rise to compensating subsidence in the surrounding regions of Cambodia and Philippines, which suppresses convection and produces cooling over there. These cooling anomalies over warm pool and surrounding regions of Cambodia and Philippines could be more effective at generating a rotational flow convergence response (i.e., cyclonic circulation anomaly) at latitude 25°N over China multiplied by the larger subtropical Coriolis parameter to produce a forcing term in the vorticity equation [ DeWeaver and Nigam , 2004; Yadav et al , 2009]. The cyclonic circulation anomaly due to convergence intensifies the Asian westerly jet stream over Indian region (Figure 7b).…”

Characteristic features of winter precipitation and its variability over northwest India

“…In the earlier studies by Yadav et al (2007Yadav et al ( , 2009aYadav et al ( , 2009bYadav et al ( , 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 …”

Assessing impact of climate change on season length in Karnataka for IPCC SRES scenarios

“…Some of the examples of predictors (variables and indices) chosen in previous studies in predicting Indian Monsoon rainfall are sea surface temperatures (SSTs), mean sea level pressure (MSLP), geopotential height and wind fields, Eurasian snow cover and surface temperatures, the Ninõ-3 SST anomaly, the Europe pressure gradient, the south Indian Ocean SST index, and north Atlantic SST (Yadav et al 2007(Yadav et al , 2009a(Yadav et al , 2009b(Yadav et al , 2010b.…”