Decreasing trend in the strength of Tropical Easterly Jet during the Asian summer monsoon season and the number of tropical cyclonic systems over Bay of Bengal

Abstract

[1] The NCEP/NCAR reanalysis data during the period 1958 -1998 show a positive trend in the 100 hPa zonal wind, decrease in the strength of Tropical Easterly Jet (TEJ) during the summer monsoon period of June through September. This is confirmed by the Radiosonde data. The number of observed Tropical Cyclonic Systems (TCS) over Bay of Bengal during the same period shows a decreasing trend. There is a strong negative correlation (À0.549 for the period 1958 -1998, 41 years, significant at 99.9% level by a two sided student t test) between the strength of TEJ and the number of Bay of Bengal TCS. This result has potential for long-range prediction of TCS, which is vital for the prediction of monsoon rainfall.

Long Term Spatiotemporal Variability in Rainfall Trends over the State of Jharkhand, India

“…Sathiyamoorthy and Rao et al found a reduction in strength of Tropical Easterly Jet Stream during monsoon in the recent five decades, which are responsible for the formation of monsoon depressions during the southwest monsoon season, and that are the important rain bearing systems during the southwest monsoon season [31,32]. The decrease in frequency of cyclonic storms over Indian seas during 1981-1997 have been reported by Ray and Srivastava [33].…”

An observational evidence of decrease in Indian summer monsoon rainfall in the recent three decades of global warming era

“…In the consequent study, Naidu et al (2011b) observed that a significant reduction in the frequency of summer monsoon cyclonic systems over the Bay of Bengal in the global warming era is associated with a significant increase of North Atlantic Oscillation Index [NAOI], relaxation of Southern Oscillation Index [SOI] and a weak vertical zonal wind shear in the domain 5°N-22°N and 80°E-100°E. According to Srinivasa Rao et al (2004), the NCEP/NCAR reanalysis data during the period, 1958-1998 show a positive trend in the 100 hPa zonal wind i.e., a decrease in the strength of the tropical easterly jet during the summer monsoon period. If we examine the global temperature trends in the recent past decades, twelve years reported the warmest [1998, 2005, 2003, 2002, 2004, 2006, 2001, 1997, 1995, 1999, 1990, and 2000].…”

Indian Monsoon Depression: Climatology and Variability

“…It was found that the number of extreme rainfall events have increased since 1976 (Goswami et al 2006). At the same time, the number of the MD has been reported decreasing since 1976 (Stowasser et al 2009, Kumar and Dash 2001, Sikka 2006, Ajayamohan et al 2010, Rao et al 2008, Rao et al 2004, Mani et al 2009). This contrasting trend -increasing extreme rainfall but reducing total number of depressions -is an interesting area that the community needs to invest resources.…”