A Study of One Local‐Scale Convective Precipitation Event Over Central Tibetan Plateau With Large Eddy Simulations

Abstract

Abstract The Weather Research and Forecasting (WRF) model with Large Eddy Simulation was employed to investigate a local‐scale convective precipitation event at Naqu (altitude of 4.5 km) over the central Tibetan Plateau (TP) on 24 July 2014. The WRF‐LES simulations with horizontal grid spacing of 200 m (CTRL) basically reproduced the rainfall pattern and evolution process compared to the observations. Five sensitivity experiments including removal the hills in east of Naqu (TER), decrease or increase of surface sensible heat flux (HFX0.67, HFX1.5), and surface latent heat flux (QFX0.67, QFX1.5) were implemented, respectively. Results show that the increase of surface heat flux and the eastern hills both enhanced the convection, which was triggered by the low‐level wind convergence. The QFX0.67 simulated the weakest precipitation among six runs, and the QFX1.5 simulated the earliest and strongest convection due to the enhanced atmospheric instability. It is found that the HFX0.67 caused the earlier convection initiation than CTRL and HFX1.5 owing to the lowest lifting condensation level and wettest low troposphere in it. Over the flat terrain in west of Naqu, weak convection was mostly affected by the surface heat flux. The product of 4.8 km wind convergence and difference between 7 km and 4.8 km equivalent potential temperature (>2 × 10−2 K/s) can partly indicate the development of low‐layer turbulence and the subsequent convection in free atmosphere. In addition, water vapor condensation (extending to 10 km) and raindrop evaporation (below 6 km) were two key phase‐change microphysical processes during the convective period even the quite low 0°C layer (∼6.5 km) over TP.

Keywords

• local‐scale convective precipitation
• surface heat flux
• Tibetan plateau
• large eddy simulations