The Connections Between Stratospheric Sudden Warming Duration In The Northern Hemisphere And Pacific Sea Surface Temperature Anomalies

The connection between Pacific sea surface temperature(SST)and stratospheric sudden warming(SSW)is investigated using the NCEP–NCAR reanalysis dataset,ERA-Interim dataset,the interpolated outgoing longwave radiation(OLR)data,Had ISST dataset and the Whole Atmosphere Community Climate Model(WACCM3).Firstly,we analyze the precursor and the effect of SSWs with different duration.Secondly,the impact of tropical SST on SSW is analyzed.Thirdly,the impact of extratropical SST on SSW is analyzed.At last,we explore the connection of SSW and extratropical atmospheric teleconnections,which are the bridges between SST and SSW.1.Using the NCEP–NCAR reanalysis dataset and ERA-Interim dataset,we diagnose the relationship between SSW strength and SSW duration.We also compare the difference between the precursors of SSWs with different duration.The different effects of SSWs with different duration on the lower troposphere are also investigated.It is found that the stronger SSWs last longer.But the linearity between the strength and duration of the minor SSWs is less justified than that of the major SSWs.The spatial distribution of geopotential height anomalies preceding major SSWs resembles the western Pacific(WP)teleconnection pattern,while the spatial distribution of geopotential height anomalies preceding minor SSWs bears similarity to the Pacific–North America(PNA)teleconnection pattern.An enhancement of the strength of both wavenumber 1 and wavenumber 2 is found before major SSWs.Before minor SSWs,wavenumber 1 is also strengthened,but wavenumber 2 is weakened.Both minor and major SSWs would last longer if there are more positive PNA and WP.The impact of long-lasting major SSWs on the temperature and circulation is compared with that of short-lasting major SSWs using ERA-Interim dataset.The composite analysis reveals that the temperature,zonal wind and northern annular mode anomalies can propagate to lower altitude during long-lasting major SSWs than short-lasting major SSWs.2.The Had ISST dataset,the NCEP–NCAR reanalysis dataset,OLR data and WACCM3 model are used to analyze the impact of two types of El Ni?o events,i.e.,eastern Pacific El Ni?o(EP-El Ni?o)and central Pacific El Ni?o(CP-El Ni?o)events,on the duration of sudden stratospheric warmings(SSWs)in Northern Hemisphere winter.It is found that although the frequency of major and minor SSWs during different types of El Ni?o shows no distinct differences,the duration of both major and minor SSWs during CP-El Ni?o is shorter than that during EP-El Ni?o.The analysis also reveals that EP-El Ni?o tends to induce positive phases of PNA and WP teleconnections,while CP-El Ni?o induces negative-phase WP teleconnection.EP-El Ni?o causes an enhancement of wavenumber 1 in the high-latitude upper troposphere and an enhancement of the upward wave flux in the high-latitude stratosphere,accompanied by a negative anomaly in Eliassen–Palm flux divergence in the subpolar stratosphere,which accounts for the longer SSW duration during EP-El Ni?o than during CP-El Ni?o.3.Using the Hadley Center Had ISST dataset and the NCEP-NCAR reanalysis dataset,this paper investigates the connection between the variability of North Pacific surface sea temperature(SST)anomalies and stratospheric sudden warmings(SSWs)in the Northern Hemisphere winter.It is found that the correlation coefficient of the warming duration and the second primary component of winter North Pacific SST anomalies(PC2)is comparable to that of the warming duration and El Ni?o and larger than that of the warming duration and the first primary component of winter North Pacific SST anomalies(PC1).The analysis also reveals that there is a 10-20 yr oscillation both in the warming duration and PC2 after 1980 which are in accordance with each other.The positive phases of PC2 are marked by more positive Pacific–North America(PNA)and Western Pacific(WP)teleconnections in the upper troposphere.Consequently,the wavenumber-1 planetary wave in the upper troposphere is strengthened and the upward Eliassen–Palm fluxes(EP fluxes)in the extratropical stratosphere are enhanced.The enhanced upward EP fluxes into the stratosphere results in a longer warming duration.The negative phase of PC2 has the opposite effect on the warming duration than the positive phase of PC2.Although PC2 SST anomalies are driven by extratropical atmospheric anomalies,WACCM3 simulations shows that the SST in the subtropical western boundary of PC2 has a feedback on the atmosphere,which will enhance the convective activity and affect the extratropical circulation and planetary wave,will ultimately have an influence on stratospheric polar vortex.4.This study has investigated the influence of different combination of PNA and WP on SSW duration using the NCEP-NCAR reanalysis data and Had ISST dataset.The pattern of positive phase of PNA(PNA+)& positive phase of WP(WP+)is most consistent with SSW precursor while that of negative phase of PNA(PNA-)and negative phase of WP(WP-)is almost opposite to SSW precursor.In phase with the change of wavenumber-1,SSW duration is largest during PNA+ & WP+ while smallest during PNA-& WP-.It is notable that the combinations of PNA+ & WP+ and PNA-& WP-have close relation with tropical SST anomalies while PNA+ & WP+ and PNA-& WP-do not.This paper analyzed the interannual variation of minor SSW in the past few decades for the first time.By using the SSW duration as a statistical indicator for the first time,we got some new findings.Especially,we found that the effect of PC2 on the SSW is greater than that of PC1.