土壤湿度非均匀性对青藏高原一次中尺度对流系统初生过程影响的数值模拟研究

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  • 1. 成都信息工程大学大气科学学院/高原大气与环境四川省重点实验室,四川 成都 610225
    2. 中国科学院西北生态环境与资源研究院/冰冻圈科学与冻土工程重点实验室,甘肃 兰州 730000
    3. 兰州大学大气科学学院,甘肃 兰州 730000

网络出版日期: 2025-05-20

基金资助

国家自然科学基金青年科学基金项目(A类)(42325502);甘肃省青年科技基金(25JRRA703);甘肃省拔尖领军人才项目

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

摘要

为探究土壤湿度非均匀性对青藏高原中尺度对流系统初生过程的影响,本文利用卫星遥感资料、地闪观测资料和再分析资料筛选出2022810日青藏高原上空的一次由孤立对流初生发展而来的中尺度对流系统个例进行观测分析和数值模拟研究。结果表明:(1)本次中尺度对流系统在弱天气强迫背景下初生于06:00(世界时),发展过程中向东北方向移动并通过合并云团不断增强,在强对流阶段伴随有闪电活动。对流初生位置附近土壤湿度存在显著的西南干、东北湿的空间非均匀分布型。(2)基于中尺度数值模式,模拟了西南侧干区受地表热力强迫作用下形成的地面辐合,及由此产生的上升气流沿土壤湿度梯度方向发展、增强至形成对流初生的时空特征。对流初生发生时刻,初生位置上空低层大气处于干绝热层结状态下,对流有效位能(对流抑制能量)为 946. 5 J·kg-1 0 J·kg-1),2 m 气温在对流初生发生前1 h达到对流温度,此时边界层高度突破自由对流高度,随后对流迅速发展并增强。(3)敏感性试验结果表明,去除土壤湿度非均匀特征后,初生对流强度减弱,位置向西移动,这与土壤湿度非均匀性改变对流初生前大气动热力和水汽条件有关,即土壤湿度非均匀性通过增强地表温度梯度从而间接增强西南侧干区感热通量,进而增强初生前地表上升运动,以及改变风场方向从而增强初生时刻该位置的地表风场和水汽的辐合强度,使得对流发展强度增大。(4)土壤湿度均一状态下,土壤湿度值的增加使地表水汽更充沛、地面风场辐合更强,进而使得水汽辐合强度增加,对流发展增强,同时较高的土壤湿度通过减小地表温度和感热通量抑制了对流初生发生前上升气流的发展强度,使对流发展过程减缓,导致对流初生的出现时间更晚。

本文引用格式

张荣平, 孟宪红, 杨显玉, 魏 倩 . 土壤湿度非均匀性对青藏高原一次中尺度对流系统初生过程影响的数值模拟研究[J]. 高原气象, 0 : 1 . DOI: 10.7522/j.issn.1000-0534.2025.00056

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.

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