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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 10
Atmos. Chem. Phys., 18, 7473-7488, 2018
https://doi.org/10.5194/acp-18-7473-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 7473-7488, 2018
https://doi.org/10.5194/acp-18-7473-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 May 2018

Research article | 30 May 2018

Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Lois Thomas1, Neelam Malap1, Wojciech W. Grabowski2,3, Kundan Dani1, and Thara V. Prabha1 Lois Thomas et al.
  • 1Indian Institute of Tropical Meteorology, Pune, India
  • 2National Center for Atmospheric Research, Boulder, Colorado, USA
  • 3Institute of Geophysics, Faculty of Physics, University of Warsaw, Warsaw, Poland

Abstract. Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB) and pseudo-adiabatic convective available potential energy (CAPE) vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs). LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

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A thermodynamic parcel analysis of several high-resolution soundings from Pune, India, investigating pre-monsoon and monsoon conditions, is carried out in this study. A simple theoretical approach for cloud base height estimation is illustrated. Results illustrate the role of surface forcing in contrasting conditions of the pre-monsoon and monsoon. Large eddy simulations, observational data, and theoretical explanation are presented.
A thermodynamic parcel analysis of several high-resolution soundings from Pune, India,...
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