Numerical Simulation Study on the Influence of Soil Moisture Heterogeneity on the Convective Initiation of a Mesoscale Convective System over the Tibetan Plateau 

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  • 1. College of Atmospheric SciencesChengdu University of Information Technology / Sichuan Key Laboratory of Plateau Atmosphere and EnvironmentChengdu 610225SichuanChina
    2. Northwest Institute of Ecological Environment and ResourcesChinese Academy of Sciences / Key Laboratory of Cryospheric Science and Frozen Soil EngineeringLanzhou 730000GansuChina
    3. College of Atmospheric SciencesLanzhou UniversityLanzhou 730000GansuChina

Online published: 2025-05-20

Abstract

In order to investigate the influence of soil moisture heterogeneity on the convective initiation stage of a mesoscale convective system over the Tibetan Plateauan typical case of mesoscale convective systemdeveloped from an isolated convective initiation process over the Tibetan Plateau on 10 August 2022is studied by observational analysis and numerical experiments using satellite remote sensing datacloud-to-ground lightning observations and reanalysis data. The results are as follows:(1Under weak synoptic-scale forcingthe convective initiation stage of the mesoscale convective system occurred at 06:00UTCthe same as after. The convective cloud then moved northeastward and intensified through merging cloudsaccompanied by lightning activity during the development of the mesoscale convective system.2Based on the mesoscale numerical model WRFwe simulated the surface convergence in the southwestern dry zone formed by surface thermal forcingas well as the development and intensification process of the updrafts caused by the surface convergence until the formation of the convective initiation with a moving direction along the soil moisture gradient. At convective initiation timethe low-level atmosphere over the convective initiation location was in a dry adiabatic state with a CAPE CINof 946. 5 J·kg-10 J·kg-1. 2 m air temperature reached the convective temperature 1h before the occurrence of convective initiationwhen the height of the planetary boundary layer was higher than the level of free convection. The convection then strengthened rapidly.3The results of the sensitivity experiments show that the removal of the soil moisture inhomogeneity weakened the intensity of the convection and shifted the position of the convective initiation westwardwhich is related to the fact that the soil moisture inhomogeneity changed the atmospheric dynamicalthermal and moisture conditions before the occurrence of the convective initiation. The soil moisture inhomogeneity indirectly increased the sensible heat flux of the dry zone located to the southwest of the convective initiation location by increasing the surface temperaturethus increasing the upward motion at surface before the occurrence of the convective initiation. Meanwhilethe direction of the wind field near the convective initiation location was also changed and thus increasing the convergence of the surface wind field and water vapor at the convective initiation timewhich led to an increase in the intensity of the convection.4Under the condition of homogeneous soil moisture distributionincreasing soil moisture led to more abundant surface water vapour and stronger convergence of the surface wind fieldwhich in turn led to an increase in the intensity of water vapour convergence and enhanced the development of convection. In additionhigher soil moisture inhibited the intensity of pre-convective initiation updraft development by decreasing surface temperature and sensible heat fluxeswhich slowed the development of convection and led to a later convective initiation time.

Cite this article

ZHANG Rongping, MENG Xianhong, YANG Xianyu, WEI Qian . Numerical Simulation Study on the Influence of Soil Moisture Heterogeneity on the Convective Initiation of a Mesoscale Convective System over the Tibetan Plateau [J]. Plateau Meteorology, 0 : 1 . DOI: 10.7522/j.issn.1000-0534.2025.00056

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