GEOPHYSICAL RESEARCH LETTERS, VOL.34,L09806,doi:10.1029/2007GL029293, 2007 Click Here for Full Article On recent interannual variability of the Arctic winter mesosphere: Implications for tracer descent David E. Siskind,1 Stephen D. Eckermann,1 Lawrence Coy,1 John P. McCormack,1 and Cora E. Randall2 Received8January2007;revised13March2007;accepted29March2007;published5May2007. [1] Observations from the Sounding of the Atmosphere Wintertime planetary wave activity, for example, can trans- with Broadband Emission Radiometry (SABER) port polar NO to lower latitudes, increasing its exposure to experiment on the NASA/Thermosphere Ionosphere dissociating sunlight and reducing the net flux of NO into Mesosphere Energetics and Dynamics (TIMED) satellite the stratosphere [Siskind et al., 2000]. show an unusual vertical displacement of the winter Arctic [3] The 2006 NO intrusions are particularly intriguing stratopause in 2006 with zonal mean temperatures at because they were observed at the end of a winter season 0.01 hPa ((cid:1)78 km) exceeding 250 K. By contrast, at the characterized by low levels of geomagnetic activity. This conventional stratopause location near 0.7 hPa ((cid:1)50 km), suggestsmesosphericmeteorologicalvariabilitywasimpor- temperatures were unusually cold. Simulations with the tant in facilitating the rapid downward transport with NOGAPS-ALPHA model suggest that these are coupled to minimal chemical loss. Randall et al. [2006] argued that an unusually warm and disturbed lower stratosphere that an unusually strong upper-level vortex led to greater con- filtered out many of the gravity waves that normally break finement of NO in the polar night. x at and above 50 km. The model also shows that downward [4] Previous work [Randall et al., 2006; Manney et al., transportinthe2006Arcticvortexwasenhancedrelativeto 2005]reliedonmeteorologicalanalysesthatwerecappedat 2005.Theseresultsmightexplainobservationsofenhanced 1 hPa. Here we analyze data from the TIMED/SABER upperatmosphericNOdescendingtotheupperstratosphere instrumentthatextendintothelowerthermospheretoreveal in 2006 and highlights the importance of gravity waves in unusual middle atmospheric temperatures at the time when modulating the coupling of the upper atmosphere with the enhancedNOwasobserved.Wecomparethree-dimensional stratosphere.Citation: Siskind,D.E.,S.D.Eckermann,L.Coy, general circulation model (GCM) simulations of this 2006 J.P.McCormack,andC.E.Randall(2007),Onrecentinterannual period to simulations of the same period in 2005. These variability of the Arctic winter mesosphere: Implications for results demonstrate that isolated descent in the mesosphere tracer descent, Geophys. Res. Lett., 34, L09806, doi:10.1029/ wasenhancedduring2006andwesuggestreasonsforthis. 2007GL029293. Finally, we suggest how understanding the variable meteo- rology of the mesospheric winter could help resolve the longstanding controversy about EPP and its effect on 1. Introduction stratospheric NO and O . x 3 [2] In early 2004 and early 2006, satellite observations haveshownunusualintrusionsofmesosphericair,enriched 2. SABER Observations in odd nitrogen (NO = NO + NO ) and carbon monoxide x 2 (CO), into the upper stratosphere [Randall et al., 2005, [5] SABER is a 10-channel broadband, limb-viewing, 2006].NOisinvolvedincatalyticdestructionofozone,and infraredradiometerwhichhasbeenmeasuringstratospheric in2004significantlyreducedupperstratosphericozonewas and mesospheric temperatures since the launch of the observed. The intrusions in 2004 were tentatively linked to TIMED satellite in December 2001. Temperature is theoccurrenceofstrongsolarstormsintheOct–Dec,2003 retrieved from the 15 mm CO emission, which is in local 2 period [Randall et al., 2005]. Solar storms and associated thermodynamic equilibrium (LTE) in the stratosphere increased geomagnetic activity will produce enhanced and lower mesosphere and in non-LTE in the middle to energetic particle precipitation (EPP), especially in the upper mesosphere and lower thermosphere (MLT). Initial 90–110 km altitude region. These EPP events will dissoci- temperatures from anon-LTEretrieval havebeen presented ateN andproducelargeamountsofNO .Oneofthemore by Mertens et al. [2004]. Siskind et al. [2005] show they 2 x intriguing questions in aeronomy is under what circum- agreed well with ground-based OH* airglow temperatures. stances this NO can be transported down through the Here we use retrievals with the non-LTE effects included mesosphere to the stratosphere where it can react with (Version 1.06 in the SABER database). stratospheric ozone. One key element is to isolate the NO [6] Figure 1 shows zonal-mean SABER temperatures on in polar night to prevent its dissociation by solar UV. 13 February for 2005 and 2006, dates chosen using the workofRandalletal.[2006,Figure4]asaguide.In2005, thetemperaturestructureissimilartostandardclimatologies 1SpaceScienceDivision,NavalResearchLaboratory,Washington,DC, [Randeletal.,2004].However,in2006anunusualvertical USA. 2Laboratory for Atmospheric and Space Physics, University of displacement of the polar stratopause to (cid:1)0.01 hPa Colorado,Boulder,Colorado,USA. ((cid:1)80 km) is seen: additionally, the 0.2–5 hPa region is unusuallycoldandthelowerstratosphereat20–100hPais Copyright2007bytheAmericanGeophysicalUnion. anomalously warm, associated with a major stratospheric 0094-8276/07/2007GL029293$05.00 L09806 1 of 5 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 3. DATES COVERED 2007 2. REPORT TYPE 00-00-2007 to 00-00-2007 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER On recent interannual variability of the Artic winter mesosphere: 5b. GRANT NUMBER Implications for tracer descent 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION Naval Research Laboratory,Space Science Division,4555 Overlook REPORT NUMBER Avenue SW,Washington,DC,20375 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES The original document contains color images. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF ABSTRACT OF PAGES RESPONSIBLE PERSON a. REPORT b. ABSTRACT c. THIS PAGE 5 unclassified unclassified unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 L09806 SISKIND ETAL.:MESOSPHERIC INTERANNUALVARIABILITY L09806 Figure 1. Zonal mean daily averaged SABER temperatures (K). warming (available at http://www.wmo.ch/web/arep/gaw/ [10] Six 14-day hindcasts were performed. Three were arctic_bull/arctic-bulletin-2005–2006.pdf) [also Manney et initializedon31January,2005andthreewereinitializedon al.,2005].SABERtemperaturesduringthepriortwoweeks 31January,2006,allat0UTC.Foreachyear,onerunused show a gradual development of this displaced polar strato- a Rayleigh friction (RF) profile as a simple invariant proxy pause structure, with zonal mean temperatures at 1 hPa for mesospheric gravity wave drag (GWD) [see Coy et al., decreasingfromabout250Kto<210Kandtemperaturesat 2005], one run used the subgrid-scale orographic GWD 0.01 hPa increasing from <210 K to >250 K. (OGWD)parameterization ofPalmeretal.[1986],andone run was a control without RF or parameterized OGWD. Palmer et al.’s [1986] scheme is an improvement over the 3. NOGAPS-ALPHA Modeling simpleRFprofilebecauseitgivesarealisticdepictionofthe [7] To understand what might be responsible for the geographic location of mountain wave sources and also unusual temperature structure of the middle atmosphere in accountsforfilteringofmountainwavesbythebackground 2004 and 2006, and to link that structure with descent of winds. mesospheric air, we have performed simulations with the [11] Figure 2 shows zonal mean temperatures from NOGAPS-ALPHA GCM (Navy Operational Global Atmo- the six runs on the last day of the simulation (0 UTC, spheric Prediction System- Advanced Level Physics High 13 February). In 2005, the best agreement with the data in Altitude). This model has previously been used to study a Figure 1 is from runs using the parameterized OGWD and, stratospheric warming/mesospheric cooling observed by to a lesser degree, with RF. In 2006, the displaced strato- SABER in August 2002 [Coy et al., 2005] and the unusual pauseandthecoldregionnear1hPaarebestrepresentedby break-up of the Antarctic ozone hole in September 2002 the OGWD and no-drag runs. Further, imposing RF in the [Allen et al., 2006]. 2006 case yields poor agreement with the data. Thus only [8] For the present work, NOGAPS-ALPHA has been the OGWD runs capture the essential morphology of the extended in several ways. First, the model top was lifted to stratospheric temperatures in both 2005 and 2006. The 10(cid:2)4hPawith74modellevels.Ourstratosphericlong-wave similarityofthe2006OGWDsimulationtothe2006no-drag cooling scheme now transitions to the non-LTE cooling simulation and, correspondingly, of the 2005 OGWD sim- parameterization of Fomichev et al. [1998] above 75 km. ulationtothe2005RFsimulationpointsstronglytoreduced The model heating isstill asdescribed byEckermann et al. mesospheric GWD as the source of the anomalously ele- [2004], but we have improved the ozone climatology by vated Arctic winter stratopause seen by SABER in 2006, accounting for diurnal variations in the mesosphere and relative to 2005. extended it up to 10(cid:2)3 hPa based on guidance from HRDI [12] Toinvestigate the possibility of interannual variabil- and SABER data (D. Marsh, personal communication, ity in mesospheric GWD, Figure 3 shows 14-day averages 2006). All runs used a triangular truncation of T79 ((cid:1)1.5(cid:1) from the OGWD runs of zonal-mean zonal winds, mean- horizontal resolution). flow accelerations due to parameterized OGWD, and wave [9] Our NOGAPS-ALPHA ‘‘hindcast’’ runs use an ini- 1 geopotential height amplitudes. Figures 3a and 3b show tialization procedure describedbyEckermann etal.[2006]. that the zonal wind field was dramatically different for the Briefly, archived global analyses for a given date and time two years. While 2005 winds are close to climatology, the are read in on reference pressures from 1000-0.4 hPa, with 2006 winds were unusually weak in the stratosphere pole- 0.4 hPa fields extrapolated upwards and progressively wardof 50(cid:1)N,but unusuallystrong inthe mesosphere. Our blended with zonal mean wind and temperature climatolo- calculated strong upper-level cold vortex in 2006 is consis- gies to crudely initialize altitudes where analysis fields are tent with the observations of Randall et al. [2006]. absent. This global state is interpolated to the NOGAPS- [13] The interannual variation in the zonal winds has ALPHA grid, then balanced internally using nonlinear important consequences for the calculated OGWD. Thus normal mode initialization and hydrostatic adjustment pro- Figure3crevealsstrongOGWDin2005at(cid:1)0.1–1hPaand cedures prior to commencing model integrations. near 70(cid:1)N, as seen in climate GCMs with parameterized OGWD [e.g., McLandress, 1998, Figure 12]. In 2006, 2 of 5 L09806 SISKIND ETAL.:MESOSPHERIC INTERANNUALVARIABILITY L09806 Figure2. Zonalmeanmodeltemperatures,allfor0UTCforeither(top)Feb13,2005or(bottom)Feb13,2006,forruns using OGWD, RF, and no drag. however,OGWDisalmostentirelyabsentpolewardof60(cid:1)N spheric vortex yields an anomalously strong cold vortex in because the weak lower stratospheric zonal winds theupperstratosphereandmesosphere(Figure3b)[Randall (Figure 3b) filter out most mountain waves. The reduced etal.,2006].Thesefindingsareconsistentwithourgeneral mesospheric OGWD due to this weakened warm strato- understanding that the separated polar winter stratopause is Figure 3. (a) Zonal mean wind from the 2005 GCM simulation. Units are m s(cid:2)1. (b) Same as Figure 3a but for 2006. (c)MeanOGWDforthe2005simulation.Unitsarems(cid:2)1day(cid:2)1.(d)SameasFigure3cbutfor2006.(e)Meanamplitude ofperturbationwave1geopotentialheight(m)fortheperiodofthe2005NOGAPSsimulation.Thewave1amplitudewas obtained by linear regression to the perturbation geopotential at each latitude circle. (f) Same as Figure 3e but for 2006. 3 of 5 L09806 SISKIND ETAL.:MESOSPHERIC INTERANNUALVARIABILITY L09806 [15] Pseudo-CH4 isopleths in Figure 4 show a pro- nounced dip at 65–80 km in 2006 that is not present in 2005,indicatinggreaternetdownwardfluxdescentin2006 compared with 2005. The arrows in Figure 4 illustrate the changeinaltitudeforthe10and50ppbvcontoursat72(cid:1)N. Over the 2 week period, the net descent of the 10 ppbv contouris(cid:1)10kmin2006and(cid:1)6kmin2005.The50ppbv contourdescends(cid:1)6kmin2006andonly(cid:1)2kmin2005. This enhanced descent in 2006 would allow NO to more x easily reach the lower mesosphere where the chemical lifetime is longer and where it would remain confined in the strong polar vortex (Figure 3b) and thus be shielded from photodissociative loss. We thus conclude that an important factor in the enhanced downward NO (and x CO) fluxes reported by Randall et al. [2006] is greater net descentinthealtituderegionabove60kminearlyFebruary 2006. 5. Historical Context [16] Here, we speculate whether enhanced downward transport of NO also occurred in previous years. Callis et x al. [1998] argued that NO observations in 1985 could be 2 explained only if they included elevated EPP in their 2D model simulations. Contrary to this, while a link between southern stratospheric NO and EPP has been established x [Randalletal.,1998,2007;Siskindetal.,2000],Hoodand Soukharev [2006] suggest that such a link in the north is insignificant. [17] Our results here specifically show how persistent, weak zonal winds in the stratosphere can create the con- ditionsforenhancedmesosphericNO descent.Interestingly, Figure4. Contoursof‘‘pseudo-CH ’’(ppmv,seetextfora x 4 the winter of 1984–1985 was meteorologically similar to description)afterday14oftheOGWDruns.Initialpseudo- 2003–2004 [Manney et al., 2005]. Although not shown CH (dashed lines) and the final pseudo-CH (solid lines) 4 4 here,SABERtemperaturesinearly2004areverysimilarto are shown. (top) The 2005 simulation and (bottom) the 2006, consistent with the enhanced descent reported by 2006simulation.Theverticalarrowsarevisualguidestothe Randalletal.[2006].Itisthereforelikelythat1984–85was change in the altitude of the 0.01 ppmv contour (upper also a year of a displaced stratopause, and enhanced arrow) and the 0.05 ppmv contour (lower arrow) at 72(cid:1)N. descent, and, possibly, enhanced stratospheric NO as Note the greater change in 2006. 2 reported by Callis et al. [1998]. Because we do not at presentexpecttheseunusualdynamicalconditionstofollow a predictable 11 year cycle, we do not expect the NO flux gravity wave-driven [Hitchman et al., 1989], since here x into the Arctic stratosphere to follow an 11 year cycle. suppressedOGWDeliminatesit.Finally,Figure3fshowsa Contrarytomanyhistoricalmodelsimulations[e.g.,Huang high altitude planetary wave near 0.01 hPa (compare with and Brasseur, 1993], we instead expect the NO flux to Figure3efor2005).Thedissipationofthiswaveabovethis x respond to unusual weather in the middle atmosphere, altitude should lead to net poleward and downward motion which often is forced from the troposphere [e.g., Allen et via downward control [Garcia and Boville, 1994]. This, in al., 2006]. turn should contribute to at least a portion of the observed temperature increase. 6. Conclusion 4. Variation in Descent Rates [18] OurGCMsimulationscaptureimportantelementsof the unusual meteorology associated with the enhanced [14] Figure 4 plots zonal averages of a CH4-like constit- descent of NO into the upper stratosphere in January/ uent, which was advected and photochemically updated in x February 2006 (and by implication for the same period in ourOGWDruns[seeEckermannetal.,2004].Werefertoit 2004). Specifically, these include the unusually warm low- here as ‘‘pseudo-CH ’’ because it was initialized from a 4 ermost stratosphere, the unusually cold upper stratosphere, monthlyzonalmeanclimatologythatisbaseduponour2D the strong polar vortex which extends well up into the model results [McCormack and Siskind, 2002], rather than mesosphere and the displacement of the temperature peak analysis,andsocannotbecomparedwithobservations.We associated with the stratopause up to near 80 km. Our useitheretodiagnosethe relativedifferenceinnet descent results suggest that the highly disturbed lowermost strato- rates between 2005 and 2006, since it is initialized identi- sphere in 2006 blocked the propagation of gravity waves cally in each run. 4 of 5 L09806 SISKIND ETAL.:MESOSPHERIC INTERANNUALVARIABILITY L09806 which normally break in the stratopause/lower mesosphere Garcia,R.R.,andB.A.Boville(1994),‘‘Downwardcontrol’’ofthemean meridional circulation and temperature distribution of the polar winter region. Since this dynamical forcing normally would warm stratosphere,J.Atmos.Sci.,51,2238–2245. the 50 km region, in 2006, this region cooled radiatively Hitchman,M.H.,J.C.Gille,C.D.Rodgers,andG.Brassseur(1989),The leading to a strong upper-level vortex. At the same time, a separatedpolarwinterstratopause:Agravitywavedrivenclimatological planetary wave 1 propagated into the upper mesosphere. feature,J.Atmos.Sci.,46,410–422. Hood,L.L.,andB.E.Soukharev(2006),Solarinducedvariationsofodd Thebreakingofthiswavemayhaveprovidedamomentum nitrogen:MultipleregressionanalysisofUARSHALOEdata,Geophys. source which drove enhanced descent in 2006. This Res.Lett.,33,L22805,doi:10.1029/2006GL028122. enhanced descent facilitated the transport of thermospheric Huang, T. Y. W., and G. P. Brasseur (1993), Effect of long-term solar variability in a two-dimensional interactive model of the middle atmo- NO into the lower mesosphere where it remained isolated x sphere,J.Geophys.Res.,98,20,413–20,427. in the strong polar vortex. Manney,G.L.,K.Kru¨ger,J.L.Sabutis,S.A.Sena,andS.Pawson(2005), [19] Our work is incomplete in that there are still a Theremarkable2003–2004winterandotherrecentwarmwintersinthe Arcticstratospheresincethelate1990s,J.Geophys.Res.,110,D04107, numberofdeficienciesinoursimulationofthepolarwinter doi:10.1029/2004JD005367. temperatures. We fall considerably short of the 250K peak McCormack, J. P., and D. E. Siskind (2002), Simulations of the quasi- zonal mean temperature at.01 hPa in 2006. Also, even in a biennial oscillation and its effect on stratospheric H O, CH, and age 2 4 more typical year, 2005, our lower stratosphere is too cold of air with an interactive two-dimensional model, J. Geophys. Res., 107(D22),4625,doi:10.1029/2002JD002141. and our upper stratosphere/lower mesosphere is too warm. McLandress,C.(1998),Ontheimportanceofgravitywavesinthemiddle These deficiencies may be related to our neglect of non- atmosphere and their parameterization in general circulation models, orographic gravity wave drag [McLandress, 1998]. Our J.Atmos.Sol.Terr.Phys.,60,1357–1383. Mertens,C.J.,etal.(2004),SABERobservationsofmesospherictempera- model does not include chemical heating from oxygen turesandcomparisonswithfallingspheremeasurementstakenduringthe recombination [Mlynczak and Solomon, 1993] in the upper 2002 summer MaCWAVE campaign, Geophys. Res. 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