• Ajayamohan, R. S., and S. A. Rao, 2008: Indian Ocean dipole modulates the number of extreme rainfall events over India in a warming environment. J. Meteor. Soc. Japan, 86 , 245252.

    • Search Google Scholar
    • Export Citation
  • Ashok, K., Z. Guan, and T. Yamagata, 2001: Impact of the Indian Ocean dipole on the relationship between the Indian monsoon rainfall and ENSO. Geophys. Res. Lett., 28 , 44994502.

    • Search Google Scholar
    • Export Citation
  • Ashok, K., W-L. Chan, T. Motoi, and T. Yamagata, 2004: Decadal variability of the Indian Ocean dipole. Geophys. Res. Lett., 31 , L24207. doi:10.1029/2004GL021345.

    • Search Google Scholar
    • Export Citation
  • Behera, S. K., R. Krishnan, and T. Yamagata, 1999: Unusual ocean-atmosphere conditions in the tropical Indian Ocean during 1994. Geophys. Res. Lett., 26 , 30013004.

    • Search Google Scholar
    • Export Citation
  • Behera, S. K., J. J. Luo, S. Masson, S. A. Rao, H. Sakuma, and T. Yamagata, 2006: A CGCM study on the interaction between IOD and ENSO. J. Climate, 19 , 16081705.

    • Search Google Scholar
    • Export Citation
  • Chen, T. C., 1985: Global water vapor flux and maintenance during FGGE. Mon. Wea. Rev., 113 , 18011819.

  • Gadgil, S., P. V. Joseph, and N. V. Joshi, 1984: Ocean-atmosphere coupling over monsoon regions. Nature, 312 , 141143.

  • Graham, N. E., and T. P. Barnett, 1987: Sea surface temperature, surface wind divergence and convection over the tropical oceans. Science, 238 , 657659.

    • Search Google Scholar
    • Export Citation
  • Harrison, D. E., and G. A. Vecchi, 2001: January 1999 Indian Ocean Cooling Event. Geophys. Res. Lett., 28 , 37173720.

  • Kanamitsu, M., W. Ebisuzaki, J. Woollen, S-K. Yang, J. J. Hnilo, M. Fiorino, and G. L. Potter, 2002: NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83 , 16311643.

    • Search Google Scholar
    • Export Citation
  • Krishnan, R., K. V. Ramesh, B. K. Samala, G. Meyers, J. M. Slingo, and M. J. Fennessy, 2006: Indian ocean-monsoon coupled interactions and impending monsoon droughts. Geophys. Res. Lett., 33 , L08711. doi:10.1029/2006GL025811.

    • Search Google Scholar
    • Export Citation
  • Mooley, D. A., and J. Shukla, 1987: Variability and forecasting of the summer monsoon rainfall over India. Monsoon Meteorology, C. P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 26–59.

    • Search Google Scholar
    • Export Citation
  • Rajeevan, M., J. Bhate, J. D. Kale, and B. Lal, 2006: High resolution daily gridded rainfall data for the Indian region: Analysis of break and active monsoon spells. Curr. Sci., 91 , 296306.

    • Search Google Scholar
    • Export Citation
  • Rao, S. A., and S. K. Behera, 2005: Subsurface influence on the SST in the tropical Indian Ocean: Structure and interannual variability. Dyn. Atmos. Oceans, 39 , 103135.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., N. A. Rayner, T. M. Smith, D. C. Stokes, and W. Wang, 2002: An improved in situ and satellite SST analysis for climate. J. Climate, 15 , 16091625.

    • Search Google Scholar
    • Export Citation
  • Roeckner, E., and Coauthors, 2003: The atmospheric general circulation model ECHAM5—Part I: Model description. Max Planck Institute for Meteorology Rep. 349, 140 pp.

    • Search Google Scholar
    • Export Citation
  • Roeckner, E., and Coauthors, 2006: Sensitivity of simulated climate to horizontal and vertical resolution in the ECHAM5 atmosphere model. J. Climate, 19 , 37713791.

    • Search Google Scholar
    • Export Citation
  • Saji, N. H., B. N. Goswami, P. N. Vinayachandran, and T. Yamagata, 1999: A dipole mode in the tropical Indian Ocean. Nature, 401 , 360363.

    • Search Google Scholar
    • Export Citation
  • Shukla, J., 1987: Interannual variability of monsoon. Monsoons, J. S. Fein and P. L. Stephens, Eds., John Wiley and Sons, 399–464.

  • Xavier, P. K., and B. N. Goswami, 2007: An analog method for real-time forecasting of summer monsoon subseasonal variability. Mon. Wea. Rev., 135 , 41494160.

    • Search Google Scholar
    • Export Citation
  • Xie, P., and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observation, satellite estimates and numerical model outputs. Bull. Amer. Meteor. Soc., 78 , 25392558.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 3 3 3
PDF Downloads 2 2 2

Unusual Central Indian Drought of Summer Monsoon 2008: Role of Southern Tropical Indian Ocean Warming

View More View Less
  • 1 Indian Institute of Tropical Meteorology, Pune, India
Restricted access

Abstract

While many of the previous positive Indian Ocean dipole (IOD) years were associated with above (below)-normal monsoon rainfall over central (southern) India during summer monsoon months [June–September (JJAS)], the IOD event in 2008 is associated with below (above)-normal rainfall in many parts of central (southern peninsular) India. Because understanding such regional organization is a key for success in regional prediction, using different datasets and atmospheric model simulations, the reasons for this abnormal behavior of the monsoon in 2008 are explored. Compared to normal positive IOD events, sea surface temperature (SST) and rainfall in the southern tropical Indian Ocean (STIO) in JJAS 2008 were abnormally high. Downwelling Rossby waves and oceanic heat advection played an important role in warming SST abnormally in the STIO. It was also found that the combined influence of a linear warming trend in the tropical Indian Ocean and warming associated with the IOD have resulted in abnormal warming of the STIO. This abnormal SST warming resulted in enhancement of convection in the southwest tropical Indian Ocean and forced anticyclonic circulation anomalies over the Bay of Bengal and central India, leading to suppressed rainfall over this region in JJAS 2008.

The above mechanism is tested by conducting several model sensitivity experiments with an atmospheric general circulation model (AGCM). These experiments confirmed that the subsidence over central India and the Bay of Bengal was forced mainly by the anomalous warming in the STIO region driven by coupled ocean–atmosphere processes. This study provides the first evidence of combined Indian Ocean warming, associated with global warming, and IOD-related warming influence on Indian summer monsoon rainfall. The combined influence may force below-normal rainfall over central India by inducing strong convection in the STIO region. The conventional seesaw in convection between the Indian subcontinent and the eastern equatorial Indian Ocean may shift to the central equatorial Indian Ocean and the Bay of Bengal if the central Indian Ocean consistently warms in the global warming scenario.

Corresponding author address: Dr. Suryachandra A. Rao, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, NCL Post, Pashan, Pune 411008, India. Email: surya@tropmet.res.in

Abstract

While many of the previous positive Indian Ocean dipole (IOD) years were associated with above (below)-normal monsoon rainfall over central (southern) India during summer monsoon months [June–September (JJAS)], the IOD event in 2008 is associated with below (above)-normal rainfall in many parts of central (southern peninsular) India. Because understanding such regional organization is a key for success in regional prediction, using different datasets and atmospheric model simulations, the reasons for this abnormal behavior of the monsoon in 2008 are explored. Compared to normal positive IOD events, sea surface temperature (SST) and rainfall in the southern tropical Indian Ocean (STIO) in JJAS 2008 were abnormally high. Downwelling Rossby waves and oceanic heat advection played an important role in warming SST abnormally in the STIO. It was also found that the combined influence of a linear warming trend in the tropical Indian Ocean and warming associated with the IOD have resulted in abnormal warming of the STIO. This abnormal SST warming resulted in enhancement of convection in the southwest tropical Indian Ocean and forced anticyclonic circulation anomalies over the Bay of Bengal and central India, leading to suppressed rainfall over this region in JJAS 2008.

The above mechanism is tested by conducting several model sensitivity experiments with an atmospheric general circulation model (AGCM). These experiments confirmed that the subsidence over central India and the Bay of Bengal was forced mainly by the anomalous warming in the STIO region driven by coupled ocean–atmosphere processes. This study provides the first evidence of combined Indian Ocean warming, associated with global warming, and IOD-related warming influence on Indian summer monsoon rainfall. The combined influence may force below-normal rainfall over central India by inducing strong convection in the STIO region. The conventional seesaw in convection between the Indian subcontinent and the eastern equatorial Indian Ocean may shift to the central equatorial Indian Ocean and the Bay of Bengal if the central Indian Ocean consistently warms in the global warming scenario.

Corresponding author address: Dr. Suryachandra A. Rao, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, NCL Post, Pashan, Pune 411008, India. Email: surya@tropmet.res.in

Save