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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2016-591
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Dec 2016
Review status
This discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The revised manuscript was not accepted.
Role of surface hydrology in determining the seasonal cycle of Indian summer monsoon in a general circulation model
Shubhi Agrawal1 and Arindam Chakraborty1,2 1Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru, India
2Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru, India
Abstract. Rainfall during summer monsoon season (June–September; JJAS), that accounts for about 80 % of the yearly total over Indian region, is herald by its onset over Kerala in June. And these four summer monsoon months contribute 19 %, 32 %, 29 % and 20 % of the seasonal rainfall, respectively. Therefore, it is important that this seasonal cycle is captured by general circulation models (GCMs) used to understand and predict monsoon. In this study, using decade-long simulations of an atmospheric GCM, we show that surface hydrology over India as well as over its surrounding regions plays a central role during the onset phase of monsoon and thus modulates seasonal cycle. The model, in its default configuration, simulates early onset and excess precipitation (about double of that observed) over the Gangetic plain (GP) in June. Moreover, the model has large positive surface soil moisture bias over India throughout the year and negative bias over the arid-semiarid regions to the north-west of India during the pre-monsoon months. From multiple sensitivity experiments, it is discerned that the remote dry soil moisture bias in the model over the Western Central Asia region intensifies the tropospheric low-level circulation causing excessive moisture advection, followed by moisture convergence over the GP in the beginning of June, and an early onset. Local soil moisture over GP makes a diminutive contribution to precipitation bias in June. But as the season progresses and the remote influence weakens, the increased local soil moisture regulates surface and near-surface conditions which subsequently reduces moisture convergence over GP, reducing precipitation in the later phase of monsoon. The results presented here can be useful for diagnosis and improvement of land surface models.

Citation: Agrawal, S. and Chakraborty, A.: Role of surface hydrology in determining the seasonal cycle of Indian summer monsoon in a general circulation model, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2016-591, 2016.
Shubhi Agrawal and Arindam Chakraborty
Shubhi Agrawal and Arindam Chakraborty

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Short summary
In this paper we show the effects of local and remote soil moisture in determining the annual cycle of rainfall over Gangetic plain, an agriculturally important valley over northern India. This work will generate several more studies to understand the interannual variation of monsoon over India that is linked to this proposed mechanism, both in observations and numerical models.
In this paper we show the effects of local and remote soil moisture in determining the annual...
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