Preprints
https://doi.org/10.5194/acp-2022-221
https://doi.org/10.5194/acp-2022-221
 
19 Apr 2022
19 Apr 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Triggering effects of large topography and boundary layer turbulence over the Tibetan Plateau on convection

Xiangde Xu1, Yi Tang1,2, Yinjun Wang1, Hongshen Zhang3, and Mingyu Zhou4 Xiangde Xu et al.
  • 1State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
  • 2School of Environmental Studies, China University of Geosciences, Wuhan, China
  • 3Peking University, Beijing, China
  • 4National Marine Environmental Forecasting Center, Beijing, China

Abstract. In this study, we analyze the diurnal variations and formation mechanism of low clouds at different elevations. We further discuss whether there exist triggering mechanism for convection over the Tibetan Plateau (TP), and whether there is an association among low air density, strong turbulence and ubiquitous “popcorn‐like” cumulus clouds. The buoyancy term (BT) and shear term (ST) over the TP are significantly greater than those at the low elevation, which is favorable for the formation of increasing planetary boundary layer height (PBLH), and also plays a key role in the convective activities in the lower troposphere. The lifting condensation level (LCL) increases with the increasing of PBLH-LCL over the TP. From the viewpoint of global effects, the triggering effects of the dynamical structure within the boundary layer on convective clouds in the northern hemisphere are analyzed. There are strong ST and BT at two high elevation regions (TP and Rocky Mountains), and the strong thermal turbulence results in obvious positive value of PBLH-LCL at high elevation regions under low RH condition in the northern hemisphere. The values of PBLH-LCL slightly greater than zero correspond spatially to more low cloud cover (LCC) in the central part of Rocky Mountains, but obvious large-scale subsidence on both sides of the mountain leads to strong inversion above PBL and lower RH in PBL, which further lead to less LCC in these areas. Thus less LCC is generated at Rocky Mountains compared to the TP.

Xiangde Xu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-221', Anonymous Referee #1, 30 May 2022
  • RC2: 'Comment on acp-2022-221', Anonymous Referee #2, 29 Aug 2022

Xiangde Xu et al.

Xiangde Xu et al.

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Short summary
The vertical motion over the TP is associated with the anomalous convective activities. The diurnal variations and formation mechanism of low clouds over the TP and low elevation regions are analyzed. We further discuss whether there exists “high efficiency” triggering mechanism for convection over the TP, and whether there is an association among low air density, and strong turbulence and ubiquitous popcorn like cumulus clouds.
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