The Impact Of Intraseasonal Oscillations In The Mid- And High-latitude Atmosphere Of Eurasia On The Sudden Warming Of The Stratosphere In Winter And Its Mechanis

Based on NCEP daily reanalysis data and S2S(Sub-seasonal to Seasonal)reforecast data,the impact of mid-high-latitude Eurasian intraseasonal oscillation(ISO)on stratospheric sudden warming(SSW)during the boreal winter is investigated by applying the fast Fourier filtering,EP flux and its divergence,Plumb wave activity flux,lead-lag correlation and other methods.Since the relationship between the mid-high-latitude Eurasian ISO and SSW has not been explored thoroughly,a case study of the ISO-SSW relationship is carried out at first.Then the leading modes of the mid-high-latitude Eurasian ISO is extracted,along with the 3-dimensional characteristics,spatial-temporal evolution and the energy origin of these two ISO modes are detected.At last,the impact of ISO leading modes on SSW and its mechanism are discussed.Conclusions are as follows:(1)A typical vortex-split event which induced by wave 2 occurred on February 11,2018.Statistical analysis indicates that the correlation is significant when mid-high-latitude ISO leads the 2018 SSW event by 9-13 days.The diagnosis of planetary wave activity indicates that stronger ISO leads to strengthened wave 2 geopotential height anomalies;then,its in-phase superposition of climatological geopotential height makes up for the upward-propagating tropospheric planetary waves,which is in favor of the onset of the 2018 SSW event.The outcome of energy conversion equations also reveals that the ISO flow gained barotropic kinetic energy and baroclinic available potential energy from the mean flow,which contributed to the onset of SSW.(2)During the period of 1979-2020,there are two leading modes over the mid-highlatitude Eurasia with the 10-30-day cycle during the wintertime,namely,the westwardpropagating ISO and the eastward-propagating ISO.The westward-propagating ISO is circumpolar by wave 1-2 in the horizontal structure,while the eastward-propagating one is dominated by wave 3-4 with smaller scale.In the vertical direction,the two modes show a quasi-barotropic structure.Moreover,the westward-propagating ISO is discovered to develop the temperature anomaly from the troposphere to the stratosphere.The energy origins of the two modes are diagnosed.The results show that the westward-propagating ISO mainly obtains baroclinic available potential energy from the tropospheric mean flow and barotropic kinetic energy from the stratospheric mean flow,while the eastward-propagating one mainly obtains baroclinic available potential energy from the mean flow in the troposphere.(3)The statistical relationship between the ISO and SSW events is carried out.The results show that the onset of SSW is significantly correlated with the westward-propagating ISO.By employing the phase division,the onset of SSW is found to prefer to occur at the time that lags Phase 2 by 7-9 days.The dynamic process of ISO impacting SSWs is investigated.Along with the westward propagation of ISO,the corresponding pattern favors the loss of the sea ice over the Barents-Kara Sea,which profits the upward-propagating planetary waves.At the same time,the ISO circulation expands the easterly anomaly,which weakens the westerly flow that favors the planetary waves of wave 1 and wave 2 to propagate upwards into the stratosphere.Finally,using the S2 S reforecast data,the influence of the westward-propagating ISO on SSW is verified by the probability density function of zonal wind anomaly.