The changing relationship between the convection over the western Tibetan Plateau and the sea surface temperature in the northern Bay of Bengal

B H Vaid,X San Liang

doi:10.1080/16000870.2018.1440869

Abstract

Using the National Oceanic and Atmospheric Administration (NOAA) sea surface temperature (SST) data, we found that the peak Indian summer monsoon season SST in the northern Bay of Bengal (NBOB) has been increased since late 1990s. Moreover, the NBOB SST reveals an increasing trend after 1999 (hereafter POST99), whereas prior to 1999 (PRE99) the trend is decreasing. During POST99, the NBOB SST facilitates a deep convection, while during PRE99 it does not seem so. A robust causality analysis also reveals a large impact on the convection and precipitation over the western Tibetan Plateau during POST99, whereas no significant causality is identified before 1999. Besides, regressions onto the NBOB SST result in a cyclonic circulation pattern and ascending winds on upper vertical levels over the western Tibetan Plateau during POST99, which are distinctly different from those during PRE99.

Highlights

The Bay of Bengal (BOB) is a northern extension of the Indian Ocean, located between India and Sri Lanka in the west, Bangladesh to the north and Myanmar (Burma) and the northern part of the Malay Peninsula to the east
The periods PRE99 and POST99 are chosen because the first leading empirical orthogonal function (EOF) mode of the POST99 tropical Pacific sea surface temperature anomalies (SSTA) has shown maximum warming in the central Pacific, whereas the PRE99 EOF1 mode shows a warming in the eastern Pacific (Xiang et al, 2013; Chung and Li, 2013; Vaid and Liang, 2015)
The mean JA SSTs for both PRE99 and POST99 are above 28 °C (Figs. 1a and b) in most of the northern part of the bay, which is conducive to enhanced convective precipitation. [Recall that, to sustain such convection, SST has to exceed a critical threshold of about 28 °C (Gadgil et al, 1984; Graham and Barnett, 1987; Lau et al, 1997)]

Summary

Introduction

The Bay of Bengal (BOB) is a northern extension of the Indian Ocean, located between India and Sri Lanka in the west, Bangladesh to the north and Myanmar (Burma) and the northern part of the Malay Peninsula to the east. Regressions onto the NBOB SST result in a cyclonic circulation pattern and ascending winds on upper vertical levels over the western Tibetan Plateau during POST99, which are distinctly different from those during PRE99. We see a substantial difference between the PRE99 and POST99 SSTs in the north BOB region: Long.

Results

Conclusion