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

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.