Variations of Indian summer monsoon rainfall induce the weakening of easterly jet stream in the warming environment?

• Published in: Global and planetary change 2011, Vol.75 (1), p.21-30
• Main Authors: Naidu, C.V., Krishna, K. Muni, Rao, S. Ramalingeswara, Bhanu Kumar, O.S.R.U., Durgalakshmi, K., Ramakrishna, S.S.V.S.
• Format: Article
• Language: English
• Subjects: circulation; Indian; Jet streams; Latent heat; latent heat flux; Monsoons; Rainfall; Running; Summer; summer monsoon; Troposphere
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2010.10.001

The 11-year running averages of all India summer monsoon rainfall during 1877–2006 reveal two extreme active monsoon epochs (1884–1894 and 1954–1964) and two extreme weak monsoon epochs (1895–1905 and 1995–2005). The NCEP/NCAR reanalysis data is available from 1948 onwards. So for the recent two epochs (1954–1964 and 1995–2005), different parameters such as mean seasonal values of air temperatures, zonal and meridional winds at two levels, 850 hPa and 150 hPa and latent heat flux in the domain of 30°E–120°E and 30°S–40°N are analyzed. Intensified easterly jet stream is observed in good monsoon epoch. India received copious amounts of rainfall during good monsoon epoch. Release of latent heat due to these high amounts of rainfall leads to high north–south temperature gradient which may be responsible for the strengthening of tropical easterly jet stream at the upper troposphere during active monsoon epoch. Opposite features are observed for weak monsoon epoch. In the period 1995–2004, with the exception of 1996, are among the warmest 10 years on record and 1998 the warmest year. India experienced a weak summer monsoon epoch (1995–2005) which is closely associated with weak tropical easterly jet stream. This period is very much coinciding with the warmest decade. The weakened easterly jet stream (upper troposphere) is ultimately due to the reduced moisture advection as associated with weaker surface westerlies, and thus rainfall.