Preprints
https://doi.org/10.5194/acp-2019-273
https://doi.org/10.5194/acp-2019-273
08 Jul 2019
 | 08 Jul 2019
Status: this preprint was under review for the journal ACP but the revision was not accepted.

The effect of low density over the “roof of the world” Tibetan Plateau on the triggering of convection

Yinjun Wang, Xiangde Xu, Mingyu Zhou, Donald H. Lenschow, Xueliang Guo, Yang Zhao, and Bin Chen

Abstract. We study the relationships between convective characteristics and air density over the Tibetan Plateau (TP) from the perspective of both climate statistics and large eddy simulation (LES). First, based on climate data, we found that there is stronger thermal turbulence and higher frequency of low cloud formation for the same surface relative humidity over the eastern and central TP compared with the eastern monsoon region of China. Second, we focus on the dynamical and thermal structure of the atmospheric boundary layer (ABL) with low air density. With the same surface heat flux, a decrease in air density enhances the buoyancy flux, which increases the ABL depth and moisture transport from the subcloud layer into the cloud layer. With the same low cloud cover for different air densities, the greater ABL depth for lower air density means that the average mixed-layer relative humidity with higher air density will be greater than that with low air density. Results from a subcloud convective velocity scaling scheme were compared with LES results, which indicated that the original fixed parameter values in this scheme may not adequate in case of lower relative humidity and weaker thermal turbulence in the subcloud layer.

Yinjun Wang, Xiangde Xu, Mingyu Zhou, Donald H. Lenschow, Xueliang Guo, Yang Zhao, and Bin Chen
Yinjun Wang, Xiangde Xu, Mingyu Zhou, Donald H. Lenschow, Xueliang Guo, Yang Zhao, and Bin Chen
Yinjun Wang, Xiangde Xu, Mingyu Zhou, Donald H. Lenschow, Xueliang Guo, Yang Zhao, and Bin Chen

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Short summary
We study the relationships between convective characteristics and air density over the Tibetan Plateau from the perspective of both climate statistics and large eddy simulation. We find that smaller air density lead to stronger thermal turbulence which favors the formation and development of convective cloud. The original fixed parameter values in subcloud convective velocity scaling scheme may not adequate in case of lower relative humidity and weaker thermal turbulence in the subcloud layer.
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