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投稿时间:2021-08-18 修订日期:2022-08-14
投稿时间:2021-08-18 修订日期:2022-08-14
中文摘要: 为探讨粤港澳大湾区城市群对局地极端强降水的影响,采用WRF-ARW中尺度区域数值模式及GSI-3DVar同化系统,以ECMWF提供的ERA5再分析资料作为模式初始场和边界场,并进行多普勒雷达资料的三维变分同化,对2020年5月22日发生在大湾区的极端强降水过程进行数值模拟,研究城市对局地极端降水的影响过程与机理。结果表明:相较于未同化任何观测资料,加入雷达反射率和径向风资料的同化可提升降水的模拟能力,尤其对250 mm以上的特大暴雨量级的模拟改善效果最为显著;观测与对照试验共同表明,大湾区城市群一方面作为“热源”,通过感热和潜热过程提高了边界层大气温度,产生明显热岛效应的同时增强了低层大气的对流不稳定度,另一方面,较强的摩擦耗散过程使边界层风速减弱,更多的暖湿空气被截留在城市区域内部,有助于形成更强的热力不稳定与水汽辐合条件,从而使强降水中心落在城市区域边缘靠内部一侧;城市下垫面被替换为农田的敏感性试验进一步表明,城市下垫面造成的摩擦耗散作用可影响800 hPa以下的边界层,而缺乏城市冠层的摩擦耗散作用,边界层更强的西南风可将暖湿不稳定空气输送至城市区域下游更远处,并受到局地地形的强迫抬升,引起更强的垂直上升运动,从而造成比对照试验强度更大、落区位置更偏于城市下风方的降水中心。
Abstract:In order to explore the impacts of urban agglomeration in the Guangdong-Hong Kong-Macao Greater Bay Area on localized extreme heavy rainfall, this paper conducts 3DVar assimilation of Doppler radar data to simulate an extreme heavy rainfall event that occurred in the Greater Bay Area on 22 May 2020, based on the WRF-ARW mesoscale numerical model, GSI-3DVar assimilation system and ERA5 reanalysis data provided by ECMWF. The influence process and mechanism of urban area on local extreme rainfall are studied. The results show that, compared with no assimilation of any observational data, adding the assimilation of radar reflectivity and radial wind data can improve the simulation ability of precipitation, especially for the heavy rainstorm magnitude of more than 250 mm. Observation and control experiment jointly show that the urban agglomeration in the Greater Bay Area acts as a local “heat source”, increasing the temperature of the boundary layer through sensible and latent heat, resulting in significant heat island effect, which then strengthens the convective instability within lower atmosphere. On the other hand, strong friction dissipation reduces the wind speed in boundary layer so that it catches more warm and moist air within the urban area, forming stronger thermal instability and moisture convergence, and then leading to the rainfall center located at the inner part of the edge of urban area. The sensitivity experiment (i.e., removal of urban land use) further shows that friction dissipation caused by urban underlying surface affects dynamic thermodynamic environments in boundary layer below 800 hPa, resulting in stronger southwesterly and unstable atmospheric condition over downstream of the urban area in urban removal experiment. Also, the convection is lifted by the local topography, enhancing vertical upward movement, which finally results in stronger rainfall intensity than the control experiment and the location of the rainfall area more inclined to the downstream of the urban area.
文章编号: 中图分类号:P435 文献标志码:
基金项目:国家重点研发计划(2019YFC1510400)、广东省基础与应用基础研究重大项目(2020B0301030004)共同资助
引用文本:
柯宗贤,王东海,曾智琳,张春燕,梁钊明,张宇,2023.粤港澳大湾区下垫面对“5·22”极端强降水过程影响的研究[J].气象,49(1):12-26.
KE Zongxian,WANG Donghai,ZENG Zhilin,ZHANG Chunyan,LIANG Zhaoming,ZHANG Yu,2023.Underlying Surface Effect on the Extreme Heavy Rainfall Event on 22 May 2020 in the Guangdong-Hong Kong-Macao Greater Bay Area[J].Meteor Mon,49(1):12-26.
柯宗贤,王东海,曾智琳,张春燕,梁钊明,张宇,2023.粤港澳大湾区下垫面对“5·22”极端强降水过程影响的研究[J].气象,49(1):12-26.
KE Zongxian,WANG Donghai,ZENG Zhilin,ZHANG Chunyan,LIANG Zhaoming,ZHANG Yu,2023.Underlying Surface Effect on the Extreme Heavy Rainfall Event on 22 May 2020 in the Guangdong-Hong Kong-Macao Greater Bay Area[J].Meteor Mon,49(1):12-26.