罗斯贝波和局地瞬变强迫对中国东部春季一次强降水事件的影响

Impacts of Rossby wave propagation and local transient forcing on a heavy spring precipitation event in eastern China

  • 摘要: 为探讨2023年4月初中国东部极端强降水事件大气环流异常的演变机理,基于逐日NCEP再分析资料,通过诊断罗斯贝波能量频散和瞬变波强迫,研究了罗斯贝波传播和局地瞬变波强迫在欧亚中高纬度大气环流“双阻”形势建立与维持过程的作用以及可能的前兆信号,提出了中高纬度“双阻”型环流分布影响2023年4月初中国东部极端强降水的可能机制,结果指出:前期极涡较强,类似极地欧亚遥相关(类POL)作用引起乌拉尔山至东北亚地区高压脊发展,由北大西洋强降水激发的罗斯贝波向下游传播,在上游罗斯贝波和贝加尔湖西部冷空气瞬变强迫的共同作用下,乌拉尔山至东北亚地区上空形成较为稳定的“+−+”型,即“乌拉尔山阻塞高压、贝加尔湖低压槽和东北亚阻塞高压”型双阻分布形势:乌拉尔山、东北亚阻塞高压为异常热源,具有上下相当正压结构;贝加尔湖低压槽为异常冷源,上下为斜压结构;“双阻”型环流分布中的经向风异常增大了冷(暖)空气的向南(北)输送,当副热带西风急流中频散到中国东部的弱波动与中高纬度罗斯贝波同位相叠加时,中高纬度“+−+”型罗斯贝波向南伸展,加强经向风。在低空反气旋西南侧较强的南风和东北亚阻塞高压下沉气流增温的共同作用下,中国东部显著增温,随着贝加尔湖西部强冷空气下沉南压,中国东部相继形成了强冷锋、气旋和切变线,产生暴雪、寒潮、强对流和强降水天气。当北大西洋再次激发罗斯贝波向下游传播时,北大西洋东部阻塞高压加强东移,乌拉尔山阻塞高压减弱崩溃,中国东部降水结束。

     

    Abstract: To explore the evolution mechanism of atmospheric circulation anomalies during the extreme heavy precipitation event in eastern China in early April 2023, Rossby wave energy dispersion and transient forcing are diagnosed based on the NCEP daily reanalysis dataset. Impacts of Rossby wave propagation and local transient wave forcing on the establishment and maintenance of the double-blocking circulation distribution in the middle to high latitudes over Eurasian region and possible precursor are investigated, and possible mechanisms behind the double-blocking circulation distribution in the middle to high latitudes that affected the extreme heavy precipitation in eastern China in early April 2023 are explored. Results are as follows. Under the strong polar vortex in earlier period, a teleconnection similar to the polar Eurasian distant correlation (POL) caused abnormal positive anomalies of geopotential height from the Ural Mountains to Northeast Asia. Meanwhile, Rossby waves triggered by heavy precipitation in the North Atlantic propagated downstream. The combined effects of upstream Rossby waves and transient forcing of cold air in the west over Lake Baikal caused a relatively stable "+−+" pattern of double-blocking circulation from the Ural Mountains to Northeast Asia, namely the pattern of the "Ural Mountains blocking high, Baikal Lake trough, and Northeast Asia blocking high". The Ural Mountain blocking high and the Northeast Asia blocking high are abnormal heat sources, both of which showed a barotropic atmospheric structure; the Lake Baikal low trough is an abnormal cold source with baroclinic structure. The meridional wind anomalies under the double-blocking circulation strengthened southward (northward) transport of cold (warm) air. When the weak fluctuations of the subtropical westerly wind jet over the eastern China were in phase with Rossby waves in the middle to high latitudes, the "+−+" pattern of Rossby waves extended to the south and strengthened meridional winds. Under the combined effects of the strong southerly winds on the southwest side of the low-level anticyclone and the warming of the sinking airflow associated with the Northeast Asia blocking high, temperature increased in eastern China. When the cold air over western Lake Baikal descended and moved to the south, strong cold front, cyclone and shear line formed one after another from north to south in eastern China, leading to snowstorms, cold waves, strong convections and heavy precipitation. When Rossby waves were triggered again in the North Atlantic and propagated downstream, the eastern North Atlantic blocking high strengthened and moved eastward, the Ural Mountain blocking High was weakened and collapsed, and the precipitation in the eastern China ended.

     

/

返回文章
返回