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陆—气耦合对中国东部夏季高温事件影响的区域性差异及其可能机制

Regional Differences in the Effects of Land–Atmosphere Coupling on Summer High-Temperature Events in Eastern China and Their Possible Mechanisms

  • 摘要: 针对陆—气耦合对中国东部夏季高温事件影响的区域性差异及可能的机制,利用ERA5-Land/GLDAS-NOAH再分析资料,基于“两步法”陆—气耦合指数,分析了中国东部陆—气耦合强度的空间分布特征,并探究了其对高温事件影响的区域差异及可能机制。结果表明,中国东部极端高温事件的发生与土壤湿度关系密切,表现为明显的负相关关系。其中,东北地区及长江中下游地区最为显著,且极端高温频次与土壤湿度异常变化的主模态均为南北反位相变化的偶极型分布。进一步分析发现陆—气耦合存在明显的空间差异,土壤湿度通过陆—气耦合对高温事件的影响也存在显著差异。东北地区的高温事件更易受土壤变干导致的感热增加影响,当土壤偏干时,蒸散减弱,伴随着潜热通量减少、感热通量增加,有利于地表增温;同时该地区阻塞高压发展,存在陆面热力异常加热,最终导致东北地区高温事件频发。而在长江中下游,高温事件主要受环流演变伴随的地表能量变化影响,发生高温事件时,西太平洋副热带高压西伸发展,云量偏少且短波辐射增强,伴随着下沉运动产生的绝热加热,陆面存在异常增暖,地表温度升高,有利于蒸散增强,使得土壤湿度降低,进而维持了地表增温的正反馈,为该地区高温事件发生提供了有利的环流形势。

     

    Abstract: The analysis of land–atmosphere interactions and their impact on summer high temperature events in eastern China reveals significant regional differences. Using the “two-legged coupling index” using ERA5-Land/GLDAS-NOAH reanalysis data, we examined how these interactions influence high-temperature events. The results show a strong negative correlation between extreme high-temperature events and soil moisture. In the northeast region and the middle and lower reaches of the Yangtze River, the impact is most significant. Here, extreme high temperature events and abnormal soil moisture changes show a dipole pattern, with reverse phase changes occurring between the north and south. Further analysis reveals obvious spatial differences in land–atmosphere coupling, along with significant differences in how soil moisture influences high-temperature events. In Northeast China, these events are largely affected by increased sensible heat owing to soil drying. When soil is dry, evapotranspiration decreases, reducing latent heat flux and increasing sensible heat flux, which contributes to surface warming. At the same time, the development of blocking high-pressure systems and abnormal land surface heating eventually leads to frequent high-temperature events in Northeast China. In the middle and lower reaches of the Yangtze River, high-temperature events are mainly affected by changes in surface energy and atmospheric circulation. During these events, the West Pacific subtropical high extends westward, reducing cloud cover and increasing short-wave radiation. This leads to abnormal surface warming owing to adiabatic heating from subsidence, causing the surface temperature to rise. As a result, evapotranspiration increases, and soil moisture decreases. This creates a positive feedback loop that maintains surface warming and supports favorable conditions for high-temperature events in this region.

     

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