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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 8
Ann. Geophys., 24, 2075–2089, 2006
https://doi.org/10.5194/angeo-24-2075-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 2075–2089, 2006
https://doi.org/10.5194/angeo-24-2075-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  13 Sep 2006

13 Sep 2006

Theoretical aspects of the onset of Indian summer monsoon from perturbed orography simulations in a GCM

A. Chakraborty1, R. S. Nanjundiah2, and J. Srinivasan2 A. Chakraborty et al.
  • 1Department of Meteorology, Florida State University, Tallahassee, Florida, USA
  • 2Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India

Abstract. A theory is proposed to determine the onset of the Indian Summer Monsoon (ISM) in an Atmospheric General Circulation Model (AGCM). The onset of ISM is delayed substantially in the absence of global orography. The impact of orography over different parts of the Earth on the onset of ISM has also been investigated using five additional perturbed simulations. The large difference in the date of onset of ISM in these simulations has been explained by a new theory based on the Surface Moist Static Energy (SMSE) and vertical velocity at the mid-troposphere. It is found that onset occurs only after SMSE crosses a threshold value and the large-scale vertical motion in the middle troposphere becomes upward. This study shows that both dynamics and thermodynamics play profound roles in the onset of the monsoon.

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