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The Impact of Super Typhoon Nuri (2014) on the Structure and Strength of the Stratospheric Polar Vortex

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The Impact of Super Typhoon Nuri (2014) on the Structure and Strength of the Stratospheric Polar Vortex The impact of Super Typhoon Nuri (2014) on the structure and strength of the stratospheric polar vortex ISS HD Earth Viewing Experiment Nov 2, 2014 Super Typhoon Nuri Hannah E. ACard and Andrea L. Lang University at Albany, SUNY Cyclone WorKshop Pacific Grove, CA 28 October 2015 R EPORTS 1998 - 1999 Northern Annular Mode A Weak Vortex Regimes 1 50 hPa 40 km 10 30 0 20 0 100 10 4 1000 0 2 BacKground Oct Nov Dec Jan Feb Mar Apr -10 Fig. 1. Time-height development of the northern annular mode during the winter of 1998–1999. The indices have daily resolution and are nondimensional. Blue corresponds to positive values (strong polar vortex), and red corresponds to negative values (weak polar vortex). The contour -1 interval is 0.5, with values between Ϫ0.5 and 0.5 unshaded. The thin horizontal line indicates the approximate boundary between the troposphere and the stratosphere. B Strong Vortex Regimes A Composite of 18 Composite of 18weak Weak vortex events Vortex Events 10 30 30 km hPa 20 0 100 0 tropopause 300 10 1000 0 -90 -60 -30 0 30 60 90 -1 Lag (Days) −AO at 0 2 0 B Composite of 30 Composite of 30 Strongstrong Vortexvortex events Events the surface 10 30 30 km hPa 20 100 Fig. 3. Average sea-level pressure anomalies tropopause (hPa) for (A) the 1080 days during weak vortex 300 10 regimes and (B) the 1800 days during strong vortex regimes. 1000 0 -90 -60 -30 0 30 60 90 the PDFs, especially between the tails of the Lag (Days) curves.+AO at Values of AO or NAO index greater Fig. 2. Composites of time-height development of the northern annular mode for (A) 18 weak the surface than 1.0 are three to four times as likely during Baldwin and DunKerton 2001 vortex events and (B) 30 strong vortex events. The events are determined by the dates on which strong vortex regimes than weak vortex re- the 10-hPa annular mode values cross –3.0 and ϩ1.5, respectively. The indices are nondimensional; gimes. Similarly, index values less than Ϫ1.0 the contour interval for the color shading is 0.25, and 0.5 for the white contours. Values between are three to four times as likely during weak Ϫ0.25 and 0.25 are unshaded. The thin horizontal lines indicate the approximate boundary vortex regimes than strong vortex regimes. Val- between the troposphere and the stratosphere. ues of the daily AO index greater than 1.0 and less than Ϫ1.0 are associated with statistically Stratospheric and tropospheric annular “strong vortex regimes,” as characterized by significant changes in the probabilities of mode variations are sometimes independent of the normalized AO index (22). The average weather extremes such as cold air outbreaks, each other, but (on average) strong anomalies value (1080 days) during weak vortex re- snow, and high winds across Europe, Asia, and just above the tropopause appear to favor tro- gimes is Ϫ0.44, and ϩ0.35 for strong vortex North America (25). The observed circulation pospheric anomalies of the same sign. Oppos- regimes (1800 days). The large sample sizes changes during weak and strong vortex regimes ing anomalies as in December 1998 (Fig. 1) are contribute to the high statistical significance are substantial from a meteorological viewpoint possible, but anomalies of the same sign dom- of these averages (23). During the weak and and can be anticipated by observing the strato- inate the average (Fig. 2). strong vortex regimes the average surface sphere. These results imply a measure of pre- To examine the tropospheric circulation pressure anomalies (Fig. 3) are markedly like dictability, up to 2 months in advance, for AO/ after these extreme events, we define weak opposite phases of the AO (11) or NAO (14), NAO variations in northern winter, particularly and strong vortex “regimes” as the 60-day with the largest effect on pressure gradients for extreme values that are associated with un- periods after the dates on which the Ϫ3.0 and in the North Atlantic and Northern Europe. usual weather events having the greatest impact ϩ1.5 thresholds were crossed. Our results are The probability density functions (PDFs) of on society. not sensitive to the exact range of days used the daily normalized AO and NAO indices (24) Since the NAO and AO are known to mod- and do not depend on the first few days after during weak and strong vortex regimes are ulate the position of surface cyclones across the the “events.” We focus on the average behav- compared in Fig. 4. More pronounced than the Atlantic and Europe, we examine the tracks of ior during these “weak vortex regimes” and shift in means are differences in the shapes of surface cyclones with central pressure less than 582 19 OCTOBER 2001 VOL 294 SCIENCE www.sciencemag.org The stratospheric polar vortex Zonal mean zonal wind (m s-1) at 10 hPa and 65°N mean 80 60 40 20 Winter (Nov- Feb) 0 10 hPa height (m) −20 and wind (m s-1) −40 The winter of 2014/2015 zonal mean zonal wind 10 hPa 65°N The winter of 2014/2015 zonal mean zonal wind 10 hPa 65°N Final warming Zonal mean zonal wind rapid deceleraons The winter of 2014/2015 zonal mean zonal wind KarpetcKo and Nikulin (2004) 10 hPa 65°N Nov/Dec wave acavity is negavely correlated with Jan/Feb wave acavity 4446 JOURNAL OF CLIMATE VOLUME 17 4446 JOURNAL OF CLIMATE VOLUME 17 plane channel model. They found that, when wave forc- ing at the lower boundary isplane raised channel beyond model. a critical They found that, when wave forc- amplitude, the eddy componentsing at and the mean lower zonal boundary flow is raised beyond a critical in the stratosphere oscillateamplitude, quasiperiodically. the eddy In components their and mean zonal flow model vertically propagatingin planetary the stratosphere waves 1 oscillate and 2 quasiperiodically. In their decelerate westerly zonal flowmodel until vertically it turns into propagating east- planetary waves 1 and 2 erlies. Since planetary wavesdecelerate cannot propagate westerly in zonal east- flow until it turns into east- erlies (Charney and Drazin 1961),erlies. this Since results planetary in trapping waves cannot propagate in east- of the waves. In the absenceerlies of wave (Charney forcing and the Drazin strato- 1961), this results in trapping sphere relaxes to the radiativeof the equilibrium, waves. In thewesterlies absence of wave forcing the strato- are recovered, and waves cansphere againBacKground relaxes propagate to the into radiative the equilibrium, westerlies stratosphere. This mechanismare suggests recovered, that and the waves period can again propagate into the 4446 of oscillationsJOURNAL is determined OFstratosphere. by CLIMATE the time that This the mechanism strato- suggests that theVOLUME period17 sphere takes to relax to theof radiative oscillationsJan/Feb zonal mean zonal wind equilibrium. is determined The by the time that the strato- plane channel model. They foundperiod that, of the when vacillations wave forc- is roughlysphereWeak takes 2–3 months, to Nov/Dec wave acavity relax which to the radiative equilibrium. The Strong Nov/Dec wave acavity ing at the lower boundary iscoincides raised beyond with the a period critical of theperiod heat of flux the anticorrelation vacillations is roughly 2–3 months, which amplitude, the eddy componentsfound and here. mean zonal flow coincides with the period of the heat flux anticorrelation in the stratosphere oscillate quasiperiodically.Aconnectionbetweeneddycomponentsandmean In their found here. model vertically propagatingzonal planetary flow oscillations waves 1 and was 2 afterwardAconnectionbetweeneddycomponentsandmean found in general decelerate westerly zonal flowcirculation until it turns models into and east- inzonal observations flow oscillations (Cristiansen was afterward found in general erlies. Since planetary waves1999, cannot 2001). propagate Cristiansen in east- (2001)circulation pointed models out that and these in observations (Cristiansen erlies (Charney and Drazin 1961),oscillations this results originate in trapping from competition1999, 2001). between Cristiansen zonal (2001) pointed out that these of the waves. In the absencewind of wave deceleration forcing the caused strato- by verticaloscillations convergence originate of from the competition between zonal sphere relaxes to the radiativevertical equilibrium, component westerlies of the EPwind flux deceleration and zonal wind caused ac- by vertical convergence of the are recovered, and waves canceleration again propagate caused into by relaxation the vertical toward component the radiative of the EP flux and zonal wind ac- stratosphere. This mechanismequilibrium. suggests that Figure the 3period showsceleration the JF wind caused anomalies by relaxation for toward the radiative of oscillations is determinedyears by the with time the that weak the strato- and strongequilibrium. ND heat flux Figure as well 3 shows as the JF wind anomalies for sphere takes to relax to thetheir radiative differences. equilibrium. Only Thewintersyears when with the the ND weak normalized and strong ND heat flux as well as period of the vacillations is roughlylatitudinal 2–3 averaged months, heatwhich fluxtheir anomalies differences. at 20 OnlyhPa were winters when the ND normalized coincides with the period of themore heat (1985, flux anticorrelation 1994, 1998, 2001,latitudinal 2002) averaged or less (1980, heat flux anomalies at 20 hPa were found here. 1981, 1989, 1990, 1996, 2000)more thanJanuary/ (1985, 1 s were 1994, included 1998, 2001, 2002) or less (1980, Aconnectionbetweeneddycomponentsandmeanin these statistics. It is seen1981, that, 1989, when 1990, wave 1996, flux is 2000) than 1 s were included zonal flow oscillations was afterwardweak in the found early in winter, general thein midwinter theseFebruary zonal statistics. polar night It is jet seen that, when wave flux is circulation models and inis observations well developed (Cristiansen between 60weak8 and in 70 the8N(Fig.3a).In early winter, the midwinter polar night jet contrast, when the early winteris well heatmean zonal developed flux is strong, between the 608 and 708N(Fig.3a).In 1999, 2001).
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