Unveiling the Urban Impact on Mesoscale Convective System Rainfall in the Pearl River Delta Urban Agglomeration Under Typical Synoptic Backgrounds

IF 3.8 2区 地球科学 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES Journal of Geophysical Research: Atmospheres Pub Date : 2024-10-30 DOI:10.1029/2024JD042409
Xinguan Du, Haishan Chen, Yali Luo, Qingqing Li, Zhe Feng, L. Ruby Leung
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Abstract

Mesoscale convective systems (MCSs), the primary drivers of extreme rainfall over the Pearl River Delta (PRD) urban agglomeration, are strongly influenced by synoptic circulations and local geographical environments, including water bodies and topography. However, the urban impact on MCS rainfall under various synoptic backgrounds remain inadequately understood. Using a 20-year high-resolution MCS tracking database and self-organizing map clustering, three typical backgrounds for MCSs, namely weak monsoon-like, strong monsoon-like, and low-pressure system (Types-1 to 3), impacting the PRD are identified. These backgrounds exhibit pronounced disparities in MCS tracks and temporal variations as well as rainfall distributions. Urban heat island (UHI) significantly alters the spatial patterns under Types-1 and 2. Specifically, under weak UHI condition, MCS rainfall typically occurs offshore in the morning and shifts inland in the afternoon driven by the land-sea breeze. However, UHI modifies the low-level thermal structure, leading to anomalous convergence and instability, which causes morning rainfall to concentrate near coastal cities, while afternoon rainfall expands further inland to the northern rural region. Additionally, the strong southwesterly winds associated with Type-2 enhance the interaction between topography and urban impact, resulting in even higher rainfall anomalies (+28.9%) over the northeastern region. The findings highlight the crucial role of urban impact and their synergistic effect with synoptic backgrounds and other land surface processes on MCSs.

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揭示典型天气背景下城市对珠江三角洲城市群中尺度对流系统降雨的影响
中尺度对流系统(MCS)是珠江三角洲(PRD)城市群极端降雨的主要驱动因素,受同步环流和当地地理环境(包括水体和地形)的影响很大。然而,在不同的天气背景下,城市对流域降雨的影响仍未得到充分了解。利用20年高分辨率多云天气跟踪数据库和自组织地图聚类,确定了影响珠三角的三种典型多云天气背景,即弱季风、强季风和低压系统(类型1至3)。这些背景在多云气候系统的轨迹和时间变化以及降雨分布方面表现出明显的差异。城市热岛(UHI)显著改变了类型-1 和类型-2 的空间模式。具体来说,在弱 UHI 条件下,多云天气降雨通常在上午出现在近海,下午在海陆风的驱动下向内陆移动。然而,UHI 改变了低层热力结构,导致异常辐合和不稳定,从而使上午的降雨集中在沿海城市附近,而下午的降雨则进一步向内陆北部农村地区扩展。此外,与类型 2 相关的强西南风增强了地形与城市影响之间的相互作用,导致东北地区降雨异常值更高(+28.9%)。研究结果凸显了城市影响的关键作用,以及它们与同步背景和其他陆面过程对多变量气候系统的协同效应。
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来源期刊
Journal of Geophysical Research: Atmospheres
Journal of Geophysical Research: Atmospheres Earth and Planetary Sciences-Geophysics
CiteScore
7.30
自引率
11.40%
发文量
684
期刊介绍: JGR: Atmospheres publishes articles that advance and improve understanding of atmospheric properties and processes, including the interaction of the atmosphere with other components of the Earth system.
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