Connection between abnormal downward activity flux of Rossby waves 3-4 and cold spells in eastern China
Cold spells are significant winter weather events that affect eastern China,posing risks to public safety and property.Various factors contribute to the occurrence of these cold spells,including anomalies in the polar vortex,tropical sea surface temperature,Arctic Oscillation,and stratosphere-troposphere coupling.One key form of stratosphere-troposphere coupling is Rossby wave reflection,which can alter tropospheric circulation and trigger cold spells.Previous studies,such as Matthias and Kretschmer(2020),have linked North American cold spells to wave reflection over Siberia and Canada,primarily involving wave numbers 1 and 2.However,the characteristics of cold spells in eastern China remain underexplored,particularly those influenced by higher wave numbers.To address this gap,we analyzed cold spell events in eastern China from 2000 to 2020,selecting cases based on the intensity and duration of cooling.We calculated the E-P flux for wave components 1-4,identifying events influenced by wave reflection.From this analysis,we identified 6 cases influenced by wave reflection of waves 1-2 and 8 cases influenced by wave reflection of waves 3-4.This study focuses on the anomalies associated with Rossby waves 3-4 and their impact on cold spells in eastern China,using synthetic analysis of the 8 cases influenced by wave reflection of waves 3-4 with ERA5 reanalysis data.Our findings indicate anomalies in Rossby waves 3-4 are closely linked to the Ural high.Prior to cold spells,the stratospheric polar vortex showed a distinct 3-wave structure,with the mid-to-upper stratosphere(500-600 K)polar vortex shifting towards Eurasia and extending its northern edge to northern Europe.This dis-placement resulted in abnormal easterly zonal winds over high-latitude Eurasia,promoting downward Rossby wave activity fluxes.The lower stratospheric polar vortex(450 K)elongated towards East Asia,forming wave re-flection near the tropopause characterized by upward fluxes over western Europe and downward fluxes over east-ern Europe.This reflection pattern intensified the Ural high,facilitating the onset of cold spells in China.We pro-pose a regional reflection index,defined as the difference between the eddy heat fluxes over western Europe and eastern Europe at 200 hPa.The index peaked approximately one week before the coldest temperatures were recor-ded,demonstrating strong correlation with temperature changes associated with cold spells influenced by waves 3-4 in eastern China.This index could serve as a valuable tool for forecasting and early warning of cold spells.This study reveals that,in addition to wave components 1-2,wave reflection involving components 3-4 can also occur under specific conditions,contributing to cold spells in eastern China.Future research will examine the 6 cases influenced by wave reflection of waves 1-2,comparing the circulation characteristics and mechanisms between cold spells influenced by waves 1-2 and waves 3-4.
cold spellUral highwave reflectionpolar vortex anomalyreflection index
万方数据
维普
