The Evolution of US Aerospace Power
The Evolution of US Aerospace Power AS 2020
Utah State University
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CHAPTER 7 LEAD AUTHEIR BEINTRIELITINE AUTHEIRE Ozone and Stratospheric Chemistry M R Schoeberl A R Douglass J C Gille J A Gleason W R GTOSC C H Jackman S T Massie M P McCormick A J Miller P A Newman L R Poole R B Rood G J Rottman R S Stolarski J W Waters EDS SCIENCE PLAN CHAPTER 7 CEINTENTE 7 N w 4 u Stratospheric oz one background 711 Why is understanding stmtospheric ozone important 7111 Location of the ozone layer and climatology 7112 Ozone and UVibiological threat 7113 Ozone and climate change 712 Observed ozone changes 7121 Polar ozone changes 7122 Midlatitude ozone loss 713 The stratospheric ozone distribution 7131 Chemical processes 7132 Trans ort 7133 Aerosols and Polar Stratospheric Clouds PSCs 71331 Aerosols 71332 Polar stratospheric clouds 7134 Solar ultmviolet and energetic particles Modeling the ozone distribution assessments 7141 Twodimensional models 7142 Threedimensional models 18 gt1 4 3 Major scientific issues and measurement needs 721 Natural chan es 7211 Interannual and longterm variability of the stratospheric circulation 7212 External in uences solar and energetic particle effects 7213 Natural aerosols and PSCs 722 Manmade changes 7221 Trends in chlorine source gases 72211 Historical trends in chlorine source gases 2 12 Stratospheric chlorine 72213 Depletion of ozone by stratospheric chlorine 7222 Effects of aircra exhaust 723 Summary ofscience issues Required measurements and data sets 73 1 Meteorological requirements 732 Chemical measurement requiremenw 7321 Science questions 7322 Key trace gas measuremenw 733 Stratospheric aerosols and PSCs 734 Solar ultraviolet ux 735 Validation of satellite measurements EOS contributions 741 Improvemenw in meteorological measurements 7411 Global limb temperature measurements 7412 Higher horizontal resolution tempemture pro les 2 A 39 emica in L t 1 743 Improvemenw in measuremenw ofaerosols 744 Improvemenw in measuremenw of the solar ultraviolet ux 745 Advanced chemicaldynamicalradiative models 746 Full meteorological and chemical assimilation ofEOS data sets Foreign partners and other measurement sources Referen ces Chapter 7 Index 71 Stratospheric ozone 7 background 711 39 39 ponam n 15 kmypaned pn WMd and dawnward by m 111g 1 h m a r m mm azanz y 1 mm m wavelenghs shun4 LhanZUU m Th2 wavzlenglhs bar omnznn anleEI nm arenmwwd mun 7 1 Wm 1 MWWW WWW 3 maner 7 SM mm Mammyquot face Numemus smokes h 5 m 15 2125 harmfu 117 plants annuals and m ammunm m m mansUNMO 1992 m 1mm Amosmenc m mpznm Dressuezs nwmnmmm 71 1 17mm 1271119177771 change Ifmanz mm matasphexewuetabe 71 1 1 sphere the layerquot IPcc 12pm sphere belaw 1 km m the Egan knawn as the mg afchmate Changquot 1995 Th camlwanafthnl 1 h mu mm mm am r N u w quot cussedmchaplerA equaltathepaauvendlmve farcmgfmm hlam uamr carbunsCFCs the 5mm athz mammhmc mamlass 7112 gen 01 Th axygznammOpmn1cedby39hsphmnlyas m Shape 15m ed fax 39hatlass xecamhnes wnh 01 1 ram alum 0 0mm fuzmahm rmquot 7 a man hale Andaman at a munch WWW Salaman 199D Madam Anhnugh m chiming 1 cum mm W Pam 199D m Innges ume sums WW m w W mAmM w WWW SWIM his mm my Wm ammkm 1925 1551mmanng pg quot nh mlycanstnm V 4a a 7 39 1 c and Analysis Ufa 1am mum Navembex 1972 NxmhusJ 5am hrqnalny g am ncaxdsbegan m wnh m launchan amzm and TOMS mslmmzms Thzse h mmmmzyme smmi McMumnJSAGE ummms may NaxdumHemlsphzn whmh are My m m m mm and eulyspnng p2 mg a abmn rXV pxdzcadz m Auusw w m a HH A uua quotmy qhqa m cammnmcauan Chlanne ndxcals have been funk TOMS andSEUV mslmmems h m h h UARS MLS mmm Same a n 1997 absemd Azmsal and Gas Expnmzm SAGE mum mum k v A h 7 4 7 3 4mm mmmtymm Mow am cm 450 be m lcedby ymuhmdsmmgmm mm Mm H m CH oxhld l xhydnczrbon cm 5 ude by 3914 mags m hydmgen mm cum mum Tine made an ymceamk mmm m H mm mm mm Ho 5 at 70H mm mm msdy m mm cm S 9b 2 0 am ww quotend um um m um um n mm 2 mm sources of bromine are methyl bromide CHgBr and the halons CFgBr and CFzClBr These source molecules are transported to the stratosphere where they react or are pho todissociated to produce the catalyticallyactive oxide radicals The catalytic ef ciency of hydrogen nitrogen chlorine and bromine oxides is determined by a set of interlocking reactions which convert the active oxides to catalyticallyinactive temporary reservoirs such as HNOg HCl ClONOZ H20 HOCl HOBr and BrONOZ andvice vers a In the lower stratosphere the balance between cata lytic oxides and temporary reservoirs is strongly affected by reactions on the surfaces of stratospheric aerosols The balance is even more profoundly affected in the polar winter by reactions on the surface of Polar Stratospheric Cloud PSC particles In the early spring the chlorine balance is shifted to almost 100 Cle ClOK is short hand for the sum ofall chlorine radicals ClO ClZOZ Cl Brune et al 198939 Waters et al 1993 This shift in the chemical balance results in a large calculated chemical sensitivity of ozone towards chlorine perturbations and a relatively small calculated sensitivity of ozone towards nitrogen oxide perturbations Although the basic outline of the chemistry con trollin A 39 I 110w known 111411 i111pU1La11L aspects of the problem remain to be solved The primary difference between the Northern and Southern Hemi spheric polar ozone loss regions appears to be a result of the denitri cation that occurs in the Antarctic winter Denitri cation means the removal of nitrogen oxides and HNO by large particles which fall into the troposphere Denitri cation takes place when temperatures are cold enough to form large stratospheric ice crystals When springtime comes there are no nitrogen ox ides to convert Cle to ClONOZ and slow down the rate of ozone depletion There is some evidence for denitri cation when temperatures are not cold enough to form ice crystals Under those conditions the mechanism for denitri cation is not completely understood 7132 Transport Much of the currentlyobserved ozone interannual vari ability in the stratosphere is controlled by dwamical processes In particular this variability is drivenby such processes as the quasibiennial oscillation QBO El Ni oSouthem Oscillation tropospheric weather systems which extend into the stratosphere and longterm uc tuations in planetary wave activity The annual cycle of total ozone is largely driven by transport effects As shown in Figure 72 relatively low values of ozone are observed in the tropics and high values are observed in the extratropics These low tropical ozone values occur in spite EIZDNE AND ETRATDSF HERIC CHEMISTRY 2315 of the large ozone production rates in the tropics If ozone production were precisely balanced by ozone loss every where total ozone would have extremely high values in the tropics The observed tropical low values result from vertical advection of lowozone air from the tropical tro 39 t 39 tmtn phere and pu pl1e1t 1 transport of this air poleward and downward into the extratropics and polar regions This advective circulation is known as the BrewerDobson circulation The redistribution of ozone from the production region at low latitudes to extratropical latitudes is modu lated by a variety of processes Foremost among these processes is the annual cycle in the circulation It is now recognized that the BrewerDobson circulation is prima rily controlled by largescale waves in the winter stratosphere As these waves propagate through the west erly winds that dominate the winter stratosphere they exert a westward zonal drag which through the Coriolis force leads to a poleward and downward transport circulation which in turn drives the temperatures away from radia tive equilibrium The largescale waves breaking in the winter upper stratosphere also produce li ing in the trop ics Since the lifetime of ozone increases with pressure the poleward downward circulation causes ozone to ac cumulate in the lower stratosphere over the course of the winter Since the largescale waves are not present in the summer the poleward and downward circulation is sig ni cantly weakened and ozone amounts which have built up during winter begin to decrease due both to transport into the troposphere and to photochemistry The exchange of mass between the troposphere and the stratosphere is the focus of considerable current re search Holton et al 1995 Stratospheretroposphere exchange is important for the budget of ozone in the lower 1 t 1L 1 w ell in p p Upward transport occurs in the tropics but the exact mechanism controlling the transport is not clear Current research is focussing on the role of subvisible cirrus and the radiative impact of infrared IR heating of subvisible cirrus Jensen et al 1997 Downward transport strato sphere to troposphere takes place in midlatitudes through jet stream foldsibut the frequency and amount of mass irreversibly moving through these folds is still not under stood Holton et al 1995 7133 Aerosols andPolar Stratospheric Clouds PSCs It is now known that knowledge of stratospheric aerosols and PSCs is very important to our understanding ofstrato spheric ozone The surfaces of aerosols and PSCs are sites for heterogeneous reactions which can convert chlorine from reservoir to radical forms Likewise radical nitro 231E EEIE SCIENCE F39LAN CHAPTER 7 gen forms can be sequestered as nitric acid to shift the chemical loss process WMO 1995 71331 Aerosols Thelongterm stratospheric aerosol record reveals at least three 1 epi udic 39 PSCs and clouds just above the tropical tropopause and a back ground aerosol level At normal stratospheric temperatures aerosols are most likely supercooled solu tion droplets of HZSO4HZO with an acid weight fraction of 55 to 80 The primary source of stratospheric aero sols is volcanic eruptions that are strong enough to inject SOZ buoyantly into the stratosphere Aerosol sizes range from hundredths of a micrometer to several micrometers Although there is some variability especially just after a volcanic emption alognormal size distribution of spheri cal particles appears to aptly describe the aerosol Just a er an eruption the size distribution becomes bimodal and some particles are nonspherical because ofthe addi tion of crustal material After an eruption the S02 is converted to HZSO4 which condenses to form strato spheric sul lric acid aerosols with a time scale of about 30 days Subsequently aerosol loading decreases due to a combination of sedimentation subsidence and exchange through tropopause folds The loading decreases with an efolding time of 9to12 months although this appears quite variable with altitude and latitude The net effect of this postvolcanic dispersion and natural cleansing is a greatly enhanced aerosol concen tration in the upper troposphere after a major eruption especially poleward of about 30 latitude Except imme diately after an eruption stratospheric aerosol droplets tend to be concentrated into 3 distinct latitudinal bandsi one over the equatorial region to 30 and the other over each highlatitude region 50 to 90 N and S Following a lowlatitude eruption aerosol is dispersed into both hemispheres whereas following a midtohighlatitude eruption aerosols tend to stay primarily in the hemisphere of the eruption Potential sources of a background aero sol component include carbonyl sul de OCS from the oceans lowlevel SOZ emissions from volcanoes and various anthropogenic sources including industrial and aircraft emissions Also it is not clear whether there is an upward trend in this background aerosol as has been hy pothesized and linked to increasing aircraft emissions since any increase may be due to incomplete removal of past volcanic aerosol Stratospheric aerosol loading in 1979 was approxi mately 05 X 10mg 05 Mt thought to be representative of background aerosol conditions The present status of the aerosol is one of enhancement due to the June 1991 eruption of Pinatubo 15 1 N 12040 E which produced on the order of 30 X 10mg 30 Mt ofnew aerosol in the stratosphere about 3 times that of the 1982 eruption of El Chichon This perturbation appears to be the largest of the century perhaps the largest since the 1883 eruption of Krakatoa By early 1993 stratospheric loading de creased to approximately 13 Mt about equal to the peak loading values after El Chichon McCormick et al 1995 Measurements in 1995 showed that the aerosol levels were approaching background levels 71332 Polar Stratospheric Clouds PSCs The interannual variability in PSC sightings has been addressed by Poole and Pitts 1994 who analyzed more than a decade of data from the spacebome Strato spheric Aerosol Measurement SAM ll sensor Figure 76 They found noticeable variability in PSC sightings in the Antarctic from year to year even though the south ern polar vortex is typically quite stable and longlived This variability was found to occur late in the season and can 1111HU r A I Poole and Pitts found even more yeartoyear variability in SAM 11 Arctic PSC sighting probabilities This was expected since the characteristics and longevity of the northern polar vortex vary greatly from one year to the next The yeartoyear variability inArctic sighting prob abilities can also be explained qualitatively by differences in temperature eg zonal mean lower stratospheric tem peratures in February 1988 were as much as 20 K colder than those one year earlier 7134 Solar ultraviolet and energetic particles Since ozone formation is fundamentally linked to the lev els of ultraviolet radiation reaching the Earth natural variations in that radiation must be understood in order to detect trends The ultraviolet comprises only onetotwo percent of the total solar radiation but it displays consid erably more variation than the longer wavelength visible radiation For example from 1986 to 1990 the solar UV increased with onset of the 11year solar cycle and re sulted in an increase of global total ozone of almost 2 This natural increase in ozone is comparable to the sus i 1 nected 39 r r J need to in order to totally separate the anthropogenic decrease from this natural change Studies of total ozone trends typically subtract solar cycle and other natural changes from the total ozone record in trend resolution see WMO 199239WMO 199539 Stolarski et al 199139 and Hood and McCormack 1992 Thus morequantitative knowledge of this natural solarcycleinduced total ozone change would be especially valuable Changes in energetic particle ux from the sun penetrate into the middle atmosphere and may also drive w v Dfsnbr ansm gm gnmnhns gon hondehndladm mu mum mam ufdd7z cm a m Hm u m 25 ms m med m be de ned mm mm 1212mm ah ha Pm mmdfmmm39hvpusem m 4m cc datum mumm mm m m 7141 Mm m at Mt 39Evodmnsmrla 270 mm mnsedbysevuzl Ir seac11ng Tknmodels weald ebelruvwzofmm 5mm cumnbutnmbsm ym huddmr 2nd m 9mm x r huggnbudgdofk n been mums WM 1992wmoms Eecanseu lese weal dmyhyz m mum Mm ms mm mm magma wk 199m Amhxmsmm hwbeennohzdncmdymmnynms m s m mum m rdmy mam 5m 12 1 my Drumsz a cananhuwui Gmsehl m m a mum llywassmdmdby msmug REPsliY199LdrIAhIgEs mmdnhnmcc I39llurgzrd nssm199imd zmrgud ESLZJ cmmxwmmmkmwkmwn 0 km eukolemhoemycmmkskzb antenna zrd mhxwm on Rm 5 manned m drmmlgl39lly Mm hymn Igndlrg ma hemormmhm mg um ma Coxsde a 21 1995 3 z E 3 WWW ammmw WWmmmmmwmm 231B EEIE SCIENCE F39LAN CHAPTER 7 These 2D models have also been used to produce multiyear simulations of the response of stratospheric ozone to perturbations ofthe source gases such as CFCs from which chlorine radicals are produced WMO 199239 WMO 1995 An outstanding issue regarding simulations of the stratospheric ozone response to chlorine increases is the lack of ability of2D models to accurately predict the ozone trend in the middle and high northern latitudes over the 1980to1990 time period Since the 2D models predict a smaller trend than observed it is believed that the models do not adequately model all of the relevant processes and thus require further development 7142 Threedimensional models The threedimensional 3D or general circulation model with full interaction between chemical dynami cal and radiative processes remains elusive The present generation of general circulation models GCMs gener ates unrealistic temperature elds which in turn alter the photochemistry The unrealistic temperatures are related to problems with the model transport circulation For ex ample the polar regions are persistently cold in GCMs which suggests that there is insuf cient adiabatic heating or descent in the winter polar region Correspondingly there will be insuf cient ascent in the tropics which weak ens the transport from the troposphere into the stratosphere Subtle changes in the general circulation of the at mosphere in 3D models can alter and distort the chemical feedbacks For example Rasch et al 1995 report on a twoyear simulation using version 2 of the National Cen ter for Atmospheric Research NCAR Middle Atmosphere Community Climate Model MACCMZ A chemical scheme for 24 reactive species or families is run as part of this simulation This model is partially coupled in that the water vapor predicted by MACCMZ is connected to the chemical source of water through oxi dation of methane Prescribed ozone is used in the radiative calculation In this simulation the calculated upper strato spheric ozone is substantially lowerthanis observed39 much of the difference is attributed to the lower CH4 compared to observations by the UARS Halogen Occultation Ex periment HALOE This bias leads to excessive C10 and excessive destruction of 03 In effect the error in this long lived trace gas which results from the weak transport circulation leads to noticeable errors in ozone The dif culties described above show why most 3D modeling efforts have focused on offline calcula tions ie use of chemistry and transport models CTMs in which the wind and temperature elds are input from a GCM eg Eckrnan et al 1995 or from a data assimila tion system eg Rood et al 199139 Lefevre et al 1994 For either approach there are computational advantages as the same set of winds and temperatures is used many times Furthermore the effects of modi cations to the chemical scheme can be isolated and their effects under stood without the complications caused by feedback processes A further advantage of the use of assimilated winds and temperatures is that the results of constituent simulations may be compared directly with observations with no temperature biases such as those found in GCMs This is particularly important for the study of processes which have a temperature threshold such as heteroge neous reactions on PSC surfaces The most information is gleaned when the model is sampled in a manner con sistent with the satellite sampling Geller et al 1993 The offline approach has been used success illy for many years and is used to test chemical and transport mechanisms as well as to interpret observations These tests include 1 assessment of the importance of transport ofair with high levels of reactive chlorine to middle latitudes Douglass et al 1991 2 assessment ofthe rate ofozone loss within the North ern Hemisphere vortex and identification of the variables to which the calculation is sensitive Chipper eld et al1993 3 o e p synopticscale systems on the vortex temperature as well as their in uence on the transport and mixing of air which has experienced temperatures cold enough for PSC formation Douglass et al 1993 and 4 examination of the impact of ozone transport follow ing the breakup of the Antarctic polar vortex on the global ozone budget the ozone dilution effect These 3D studies provide a picture of the impor tant physical processes which control polar ozone loss However because of computer resource restrictions it is not yet possible to make full 3D model longrange pre dictions including possible in uence of the ozone loss on lower stratospheric temperature and climate For ex ample future temperature changes may have a signi cant impact on the Northern Hemisphere vortex The full 3D model with all relevant chemical dynamical and radia tive processes and feedbacks among them has yet to be developed EIZDNE AND ETRATDSF HERIC CHEMISTRY 2319 72 Major scienti c issues and measurement needs Changes in the ozone layer can be divided into two cat egories natural changes and manmade changes Separating these components is the goal of much ozone and trace gas research Since ozone can be transported by stratospheric winds there is signi cant interannual vari ability in column ozone amounts Ozone is likewise in uenced by aerosol amounts through heterogeneous chemistry Solomon et al 1996 the formation ofnitro gen radicals associated with highenergy particles and variations in the ultraviolet radiation from the sun Man made changes generally include increased chlorine and hydrogen amounts from industrial gases and increased aerosols and nitrogen radicals from airplane exhaust Many of our current scienti c issues and future measure ment needs center around the interaction of the ozone layer with these pollutants and separating natural changes in the ozone layer from manmade processes 72 Natural changes 7211 Interannual and longterm variability of the stratospheric circulation Because the stratospheric circulation is strongly depen dent on the dissipation of largescale waves in the stratosphere interannual variability of the wave ampli tudes has an important impact on ozone transport see Section 7132 Winds and temperatures derived from 3D GCMs and assimilation models include such interannual variability and can be used to assess the im pact on ozone transport 2D models can incorporate prescribed variability to simulate interannual ozone trans port see Section 7141 Accurate assessment of the largescale waves and the transport circulation is neces sary for understanding the variability of ozone trends One of the failures of the 3D models is inadequate simulation ofthe QBO The QBO is a 2430month os cillation of the zonal wind in the tropical lower stratosphere that is driven by tropical waves The QBO affects the stratospheric temperature distribution and pro duces a secondary circulation which transports trace gases and aerosols For ozone the QBO can generate variations from the climatological mean of510 DU in the tropics There is also a QBOozone signal outside the tropics of 1020 DU The QBO provides one of the largest components of the interannual variability of the column ozone values Because the geostrophic relationship breaks down in the tropics direct tropical wind measurements are critical to precisely measuring the QBO and for understanding the effects ofthe QBO on the circulation Datasparse regions and infrequent sampling of wind elds all preclude good quantitative studies of the tropical circulation and its ef fect on ozone 7212 External in uences solar and energetic particle e ects As discussedin Section 7134 solar ultraviolet radiation and precipitating energetic particles can strongly in u ence ozone amounts In order to understand the anthropogenic changes in ozone we must maintain reli able measurements of the solar ultraviolet input to the middle atmosphere Solar variations in the UV produce ozone changes on the same order of magnitude as the current observed midlatitude changes Proxies for the UV changes have been historically used to estimate the re sponse of ozone to solar ultraviolet changes With direct measurements from UARS these proxies have been shown to inadequately represent changes in ultraviolet ux Particle events generate NOK compounds which catalytically destroy ozone but these events tend to be con ned to the upper stratosphere Large events which tend to be more episodic may affect polar ozone at lower levels The impact of NOK generation through particle precipitation on the natural ozone layer is a major scien ti c question 7213 Natural aerosols andPSCs As discussed in Section 7133 aerosols and PSCs are believed to play a major although indirect role in ozone loss Irregular volcanic inputs of SOZ with the subsequent formation of sulfate aerosols have an impact on the ozone layer There is some evidence suggesting that increasing amounts of background aerosols are a result of subsonic aircraft emissions in the lower stratosphere A maj or sci enti c question is whether the background amounts of these aerosols are increasing and if so determining their origin Monitoring the aerosol amounts within the strato sphere and determining their trend is a primary measurement requirement to understand ozone loss During the 19805 itbecame apparent that aerosols play an important role in the chemistry of the stratosphere Observations of large decreases in ozone over Antarctica during the Southern Hemisphere spring were not ac counted for by theory until several researchers hypothesized that heterogeneous reactions on PSCs might be converting inactive chlorine compounds into reactive forms Solomon et al 198639 McElroy et al 198639 Toon et EZD EEIE SCIENCE F39LAN CHAPTER 7 al 1986 In a similar fashion to PSCs heterogeneous reactions upon sulfuric acid droplets at midlatitudes con vert N205 into HNO and shift the ratio of HNO to NOZ normally present in the stratosphere Throughout the stratosphere reactions on and inside aerosol particles are therefore important To understand the effectiveness of the heteroge neous gas phase aerosol phase reactions it is important to know a the temperatures of the aerosol particles b the surface and volume densities of the aerosol par ticles which are derived from the aerosol extinction and a knowledge of the size distribution c the composition the mixing ratios of H20 H2804 and HNO in ppbv and phase li quid solid amorphous solid solution ofthe aerosol particles d the concentration of the reactants in the aerosol eg the concentration of HCl and e the duration of time over which the heterogeneous re actions occur A theoretical framework by which heterogeneous rates of reaction are quanti ed is given in Hanson et al 1994 An important research goal is the ability to observe the yearly episodes ofozone loss in the polar regions eg the Antarctic ozone hole to measure this loss as reser voir chlorine levels change with time and to be able to relate the changes in observed ozone to a quantitative understanding of heterogeneous processes In principle one should be able to identify the com position of stratospheric aerosol from multiwavelength extinction data Multiwavelength observations of rrridlatitude sulfuric acid droplets have an extensive his tory Observations of El Chichon aerosol Pollack et al 1991 post El Chichon aerosol Osborn et al 1989 Oberbeck et al 1989 and of Mt Pinatubo aerosol Grainger et al 1993 Massie et al 1994 and Rinsland et al 1994 yield spectral data consistent with theoretical expectation Analysis of multiwavelength observations of PSCs is a developing research topic Recent attempts to use spectra to determine PSC composition are illus trated by Toon and Tolbert 1995 Several years ago ice and nitric acid trihydrate NAT particles were thought to be the primary composi tion ofPSCs Recent studies have shown that some PSC particles are liquid the ternary solution of HNOgHZO H2804 and not that of crystalline NAT Carslaw et al 1994 Drdla et al 1994 As additional laboratory cold temperature measurements of the indices of refraction of PSC composition candidates become available the abil ity to classify PSC composition from spectra will improve Although PSCs are now known to be instrumental in polar ozone loss their amounts and types must be moni tored The major difference between the Antarctic ozone depletion and the lesssevere Arctic depletion appears to be the result of a lack of denitri cation in the Arctic Schoeberl et al 1993 Fundamentally denitri cationis a function of temperature and the size of PSCs Above frost point the PSC size is generally too small to precipi tate nitric acid from the stratosphere If temperatures reach frost point larger PSCs form which are able to remove nitrogen acid from the lower stratosphere The tempera ture history of the air parcel may play an important role in the PSC size distribution as well eg Murphy and Gary 1995 Photolysis ofthe nitric acidis key to halting the ozone depletion during winter With the increase of greenhouse gases the strato sphere is expected to cool and thus increase the probability of PSC formation as well as increase the surface area and heterogeneous reaction rates on sulfate aerosols Prelimi nary studies Austin et al 1992 suggest greenhouse gas increase could have amaj or role in polar ozone depletion through increased probability of PSC formation Moni toring stratospheric aerosol loading and PSC amounts is critical for understanding ozone loss 722 Munmade changes Manmade changes in ozone mostly arise from the manu facture of unreactive chlorinecontaining compounds such as the CFCs chlorine source gases These compounds reach stratospheric altitudes where photolysis by ultra violet radiation releases chlorine with subsequent destruction of ozone through catalytic cycles Aviation also has an impact on ozone through the release of nitro gen radicals in aircraft exhaust Both of these anthropogenic effects are discussed below 7221 Trends in chlorine source gases As mentioned earlier chlorine source gases and their re spective trends are the major drivers behind decreases in A 39 A A d of chlo rine source gases is contained in WMO 1995 This report may be consulted for more detail and appropriate refer ences 72211 Historical trends in chlorine source gases All chlorine in the stratosphere comes from tropospheric sources predominantly the manmade CFCs and chlorocarbons The manmade sources account for about 78th of the total stratospheric chlorine CFCs are cur rently being phased out in favor of the hydrochloro uorocarbons HCFCs Extensive measure ments of the chloro uorocarbons CFC11 CCIgF CFC12 CClZFZ and CFC113 CClZFCClFZ have in dicated a steady increase in their tropospheric mixing ratios for more than a decade Most recent data suggest that the growth rate for these species has begun to de crease Measurements taken from Tasmania suggest that levels of the important chlorocarbon CCl4 in the tropo sphere are also decreasing As HCFCs are introduced as substitutes for CFCs it may be expected that their mixing ratios in the tropo sphere will increase well into the next century HCFC22 CHClFZ data show a nearlinear growth rate in recent years HCFC141b and HCFC142b have been available only recently as CFC replacements These species are clearly increasing in the troposphere but irther data is required to get reliable growth rates for longterm stud ies CH3CC13 data also indicate a reduced growth rate that is aresult of recentlyreduced emissions but also pos sibly due in part to increasing hydroxyl OH levels Data for dichloromethane CHZClZ methyl chloride CH3Cl and chloroform CHClg currently exhibit no longterm trends Continued tropospheric measurements of these gases are required to estimate ozone depletion potential 72212 Stratospheric chlorine An extensive compilation of measurements of chlorine source gases in the stratosphere can be found in Fraser et al 1994 The most comprehensive suites of simultaneous I in J include the Atmospheric Trace Molecule Spectroscopy ATMOS experiments of 1985 1992 and 1993 and the Airborne Arctic Stratospheric Expedition 11 AASE 11 measurements of 1991 1992 The data from these mis sions have provided invaluable information on the stratospheric chlorine burden and the partitioning among the various chlorine species Based upon the 1985 ATMOS data Zander et al 1992 determined a total stratospheric chlorine level of 255 i 028 ppbv Further they concluded that above 50 km most of the inorganic chlorine was in the form of hy drogen chloride HCl and that the partitioning of the chlorine among sources sinks and reservoir species was consistent with that level of total chlorine From the 1992 ATMOS ights total stratospheric chlorine based upon HCl data above 50 km was esti mated to be 34 i 03 ppbv anincrease of approximately 35 in seven years Gunson et al 1994 This increase is consistent with that predicted by models eg WMO 1992 Schauf er et al 1 993 inferred total chlorine lev EIZDNE AND ETRATDSF HERIC CHEMISTRY 2321 els of 350 i 006 ppbv from the AASE II data near the tropopause a value which is in excellent agreement with the 1992 ATMOS values Recent HCl data 55 km from HAL OE on UARS see Russell et al 1996 reveal atrend in HCl versus time at 55 km v 18 compared with the estimated total Cl trend based on tropospheric emissions Figure 77 Of the total stratospheric burden only about 05 ppbv is estimated to arise from natural sources in the tro posphere W MO 1995 but these estimates have yet to be con rmed by direct or remote observations HCl emis sions from major volcanic eruptions El Chichon 1982 and Mt Pinatubo 1991 provided negligible perturbations to the levels of HCl in the stratosphere Mankin and Coffey 198439 Wallace and Livingston 199239 and Mankin et al 1992 72213 Depletion ofozone by stratospheric chlorine Estimates of the severity of ozone depletion in the future can only be determined by atmospheric model simula tions The level of con dence in these models is based upon their ability to simulate present atmospheric distri butions and their ability to simulate recent decadal trends A discussion of the strengths and weaknesses of current assessment models is contained in WMO 1995 and Section 7141 Model simulations of ozone change spanning the period 1980 to 2050 were conducted as part ofthe WMO 1995 assessment process Two scenarios were adopted for the assessment studies 1 the emissions of halocar bons follow the guidelines in the Amendments to the Montreal Protocol Scenario 139 and 2 partial compliance with the guidelines Scenario H see WMO 1995 for speci c details of the scenarios and models Figure 78 pg 324 summarizes the results ofthe model calculations for Scenario 1 This gure shows the percent change relative to 1980 in the ozone column at 50 N in March for each of the models participating in the assessment Decreases ofup to approximately 65 are seen to occurjust prior to 2000 The recovery time to 1980 levels varies widely for the different models from as early as 2020 to well past 2050 The individual models all showed reasonable agreement among themselves for the presentday ozone distributions but begin to differ substantially as the atmosphere is perturbed away from its existing state by increasing levels of nitrous oxide methane halocarbons and other in uences Uncertainties in the absolute levels of depletion predicted by the models are dif cult to evaluate for these longterm scenario calculations The trends in the source gases are changing and the trends in the stratospheric reservoir gases which are dependent on transport into the 2322 EEIE SCIENCE F39LAN CHAPTER 7 stratosphere will respond Thus measurements of the chlorine source and stratospheric reservoir gases must be made to test models against observations Critical gases in the suite of required measurements are the reservoirs HCl and ClONOZ The predictive capability of these as ir Hx r Mquot I e ment of chlorine source gases reservoir gases and gases which are sensitive to transport processes 7222 E ects ofaircraft exhaust Longlived source gases eg NZO CH4 are unreactive in the troposphere and hence can enter the stratosphere at the ambient tropospheric concentrations In the strato sphere these gases undergo photolysis or react with radicals to release their potential ozonedestroying cata lytic agents In contrast aircraft ying in the stratosphere will directly inject catalytic agents into the stratosphere The primary agents for potential ozone change which have been considered in studies of aircraft exhaust are the ni trogen oxides NOX and water vapor which leads to HOX Now that heterogeneous reactions on background aero sols and PSCs are known to play an important role in the ozone balance of the stratosphere the evaluation of the effects on ozone of NOK from supersonic aircraft ying in the stratosphere has changed signi cantly T e impact on column ozone of a eet of super sonic transports now referred to as High Speed Civil Transports HSCTs is now calculated to be of the order of 1 or less An important possibility is that the sulfur in the exhaust will lead to the generation of numerous small particles which will add to the aerosol surface area An increase in surface area will enhance the conversion of chlorine from its reservoirs to Cle and thus could lead to an increased loss rate for ozone Another possibility is that the other condensibles in the exhaust water vapor and nitric acid from NOX could impact the formation or duration of PSCs Initial calculations show this effect to and lower stratosphere is not completely understood Air cra NOK sources have to be compared to the NOK sources due to lightning stratospheric intrusions and the lofting of groundlevel pollution in cumulus clouds Thus the role of aircraft as a source of upper tropospheric NOx and its impact on lower stratospheric ozone is uncertain Also uncertainis whether heterogeneous chemistry on ice crys tals plays a signi cant role in the NOK budget Understanding the impact of supersonic and sub sonic aircraft exhaust on the stratospheric chemical balance is a complex problem Knowledge of meteoro logical conditions is required to compute exhaust dispersion Knowledge of aerosol chemistry is required to understand the aerosol formation process from sul lr in fuels and its impact on the background conditions Finally a good understanding of the lower stratosphere chemistry is required to understand the direct impact of the NOK pollutants 723 Summary afscience issues The investment by the scienti c community in instru ment and model development has produced a signi cant increase in the understanding of stratospheric chemical and dwiamical processes Although some fundamental questions of ozone loss have been answered new ques tions have arisen For example the longterm response of the ozone layer to natural uctuations QBO El Ni o volcanoes is still not well understood Section 7211 The secular decrease in ozone following the eruption of Mt Pinatubo was clearly associated with aerosol loading of the stratosphereibut the nearly oneyear delay in the appearance ofmaximurn ozone loss is still not explained More fundamentally the midlatitude trend in column ozone loss reported by Stolarski et al 1991 is still not explained although it is probably connected with the in crease in stratospheric chlorine and the stratospheric chemistry associated with aerosols see Section 7133 1 L be small Considine et al 1995 and transport tquot 1quot h that inj ection into the polar vortex is unlikely Sparling et al 1995 but there is still uncertainty about what will happen as the stratosphere cools with increasing COZ con centrations All of the chemical effects of HSCT exhaust de pend on how much of the exhaust products accumulate in the stratosphere and where they accumulate The same is true for the exhaust of the subsonic eet which is released in the upper troposphere and lower stratosphere The three major potential effects of the subsonic eet of aircraft are ozone increase due to the smoglike photochemistry of NOX COZ increase due to fuel consumption and cirrus cloud formation from the water vapor The importance of aircraft NOK to ozone generation in the upper troposphere ofthe processes is still quite incomplete which increases our uncertainty in the forecast predictions Under the Atmospheric Effects of Aviation Pro gram AEAP the impact of stratospheric and tropospheric aircraft pollution on stratospheric ozone is now being in vestigated Section 7222 The research studies have 1 39 thatour quot of 1 39 transport is not complete with regard to transport espe cially the containment of the pollutants within the midlatitude release regions and the distribution and mag nitude of stratospheretroposphere exchange especially exchange of ozone Many of the issues associated with the stratospheric circulation Section 7211 are above the observing range of current stratospheric aircraft ie m mmm m as wmymmk m1 73 Required mmmementsznd dam mmmmmm mdwmsedbdm my Mormwm mm m39xrsmmm 73 1 Mupwlimulvlqmnmcm mad m Pmmw 01quot shrth mmmmm mahrgm mm mm s x mm mm 7 dzrrdzm mm ma walla rm Kc sets m Mm Hank sumsth mm 1mm 19w 1 am mm nmg fmmkmdbg d my Mm 1mm mg n 1 14px Mum Wm 2 7Janvemzl when 12 xmmm mi 3911 am you I39lzmeamnn n and mu sum e may mm medz a mam Ex mun mm mm e shun chm Mum ams mg n r m m shun muan thOAA mm m e mum gummsmKummsm Asshbdmsemm7211bw z amykva mr mumm MSUSsu mmSUweglmrg mm mmhg d duexvzcnxs m m mam m m a abouMk dzythm v W msu magmam Dfdrwmmxcmufdrlzhvaszrddrlz man mm mdmkzmylme 12mg su 14p A 1mm mm Mm ummmmmm mm st M 1 Mm m Mm mm mum W mem 021 1 mm mmm an m m mmmobmm E 2 rmchmmsmdemgnmd g 3 mm om 1P0 1995 a mm mm m s 4 Manama Thznmun 5 m 0 Monks g mmmmmxmum a quotWham m 7 mm m bum m1 SwamvemA g men ms 3911 1 u 199D 2mm 2mm 2mm 2mm 2mm 2 mnmsmm my mum avmamuwuuammmpmnmungmmumnamn wrlullm nrmmvmn km MNPOESS 459M 939 m m WWW w mm W m m Mmmm Lm Eminde MU has A Md reschmmrmfz few m 4mm karmqu avenge 5 myme gamma 1w ma mm mm nqnuemms for mm m a m u mm mm Andwmds 1P0 1996 199a 73 2 cm mmmmummm Mm suremms Whnypumymyh Andlwexshqmr 5114 3mm mm umka Mindan m magma mmms Flam mm mg Sesnlrmdrlzmemulugmzlma yses asednymmvi 7s 1 Sam mm K m k w mmmgwmecm as mmwmmmm m PM mm shamiykm wmd am a medzd Mm m M n xeg hcnns m mum mm gases mm mm lower stratospheric temperatures caused by increasing greenhouse gas concentrations For example the colder stratospheric temperatures may lead to an expansion of the extent of PSCs and hence polar ozone depletion The complex chemistry of the stratosphere can only be understood in detail by measuring a broad range of species over varying conditions with global coverage and over at least an annual cycle The rst area which merits further observational and theoretical study is polar chem istry processes Direct simultaneous measurements of HOCl or aproxy such as ClO HNOg and N205 are criti cal since these gases are believed to be involved in PSC surface chemistry Also polar night observations above 20 km ofthe chemicallyactive species along with PSC measurements are needed in understanding polar ozone depletion These regions are not presently accessible with balloons and aircraft In order to understand the large ozone depletion at 39 Section 7 1 2 21 39 measure ments of NZOS HOCl HNOg and HCl are needed to assess the role of heterogeneous chemistry on background aerosols Since OH and HOZ drive the chemistry of the lower stratosphere global measurements of these gases are required to evaluate ozone losses especially any zonal A1 0 lower 1 39 f OH and H02 along with O and temperature are likely to be key links in understanding the large O decrease expected to occur near 40 km as chlorine levels continue to rise It is clear that full understanding of these changes requires not just O and CIO measurements but HOK and NOK measurements as well Measurements in the lower meso sphere where the chemistry is more simple may provide the best data set for this analysis 7322 Key trace gas measurements There are several scienti c requirements to address middleatmosphere chemistry issues 1 The selfconsistency between the source gases and the resulting active reservoir gases needs to be tested for the four major families that are important to ozone chemistry The four families and most important spe cies measurements required are oxygen family 03 hydrogen family HZO CH4 OH HOZ HZOZ nitro gen farnily N20 N02 HNOg N205 and chlorine familyCFC13 CFZCIZ HCl C10 CIONOZ Strato spheric chlorine is predicted by atmospheric models to increase by 20 in the next ve years thus our understanding of the production and partitioning among the individual family constituents needs to be veri ed EIZDNE AND ETRATDSF HERIC CHEMISTRY 2325 2 The changes in the AntarcticArctic lower stratosphere constituents 03 HZO ClO OClO HCl BrO N20 N02 HNOg N205 and aerosols during the ozone hole period in the winter and spring need to be monitored Since signi cant changes have been detected during the 1980s and 1990s in the polar regions these geo graphical areas require special attention and monitoring 3 There are a few chemical process studies which re quire investigation as indicated below 97 The HOK family OH HOZ HZOZ is fundamen tally important in stratospheric chemistry but the database for that group remains one of the poorest in the atmosphere Global measurements of the latitudinal seasonal and diurnal variation in the HOK family and related species H20 and 03 are needed to address this de ciency ST Models for the past decade have predicted less ozone in the upper stratosphere than is measured Several species 03 O NOZ OH and C10 need to be measured in the upper stratosphere to help resolve this dif culty see Section 7141 o Models in general predict less odd nitrogen in the lower stratosphere than observed Measurements of odd nitrogen species NOZ HNOg N205 and ClONOZ in the lower stratosphere will help to deal with this problem P Another odd nitrogen species HNOg is not mod el ed accurately in the wintertime in the midtohigh latitudes Ameasurement of HNOg N205 H20 and aerosols should help confront this problem 4 V Global observations of ozone in the lowermost strato sphere tropopause to ab out 20 km with high horizontal vertical and temporal resolution are needed in order to quantify the ozone budget in that region of the atmosphere and in particular to determine the spatial and temporal distribution of ozone uxes from the lowermost stratosphere to the troposphere These uxes which are presently known only to within about a factor of two are important for the ozone budget of the lowermost stratosphere and are crucial for under standing the ozone budget of the upper troposphere The measurement requirements to attack these sci ence questions are outlined in Table 71 Generally the help one to classify regions of PSCs as to composition and phase Since the microphysics of PSC particles is very temperature sensitive absolute temperatures need to be measured to plusorminus 2 K since curves of tempera ture versus volume density for NAT ternary and NAD particles Figure 79 pg 329 differ by only a fewkelvins Remotesensing observations also average over many ki lometers along ahorizontal ray path Vertical coverage is usually on the order of several km Thus the nescale structure of PSCs as sampled by ERZ instruments can not be resolved by the remote sounder Another complication is due to present limitations in the theoreti cal understanding of howPSCs form which compositions are formed and the need for additional laboratory work to quantify at cold stratospheric temperatures the rates at which realistic PSC particles convert inactive to active chlorine compounds and the need for additional labora tory measurements of the refractive indices of PSC and sulfuric droplets Current research will see to what extent it is possible to re ne present capability to quantify the mechanisms of PSC chemistry as observed from orbit 734 Solar ultraviolet ux Solar radiation at wavelengths below about 300 nm is completely absorbed by the Earth s atmosphere and be comes the dominant direct energy input establishing the composition and temperature through photodissociation and driving much of the dynamics as well Even small changes in this ultraviolet irradiance will have important and demonstrable effects on atmospheric ozone Radia tion between roughly 200 and 300 nm is absorbed by ozone and becomes the major loss mechanism for ozone in the middle atmosphere Likewise solar radiation lt 200 nm is absorbed predominantly by molecular oxygen and becomes a dominant source of ozone in the middle atmo sphere so changes in these ultraviolet will have to rst order an inverse in uence on ozone These two atmospheric processes driven by solar radiation be come the major natural control for ozone in the Earth s stratosphere and lower thermosphere To fully understand the ozone distribution will require many coordinated ob servations and in particular a precise measurement of the solar ultraviolet ux The visible portion of solar radiation originates in the solar photosphere and has been accurately measured for about fteen years Willson and Hudson 1991 Ap parently this radiation varies by only small fractions of one percent over the 11year activity cycle of the sun with comparable variation over time scales ofa few days The ultraviolet portion of the solar spectrum comprises only about 1 approximately 10 W m39Z and originates EIZDNE AND ETRATDSF HERIC CHEMISTRY 2327 from higher layers of the photosphere As we move to shorter and shorter wavelengths the emission comes from higher and higher layers of the solar atmosphere Unlike the solar photosphere these higher levels are much more under the in uence of solar activity as manifested for example by increasing magnetic eld strength As the magnetic activity increases or disappears the solar radia tion especially the ultraviolet undergoes dramatic varia tions modulated by the 27day rotation period of the sun Near 120 nm the variation over time periods of days to weeks can be as large as 50 and over the longer 11 year solar cycle the variation can be as large as a factor of two Rottrnan 1993 Toward longer wavelengths the so lar variability decreases to levels of about 10 at 200 nm Figure 710 and nally to only about 1 at 300 nrn Longward of 300 nm the intrinsic solar variabilityis prob ably only on the order 01 roughly commensurate with measurements of total solar radiation The challenge during the EOS time period is to provide measurements of the solar ultraviolet with a pre cision and accuracy capable of tracking the changes in the solar output Ideally the instrument will be capable of measuring changes as small as one percent throughout the EOS mission This requirement is extremely challeng ing for solar instruments especially those making observations at the ultraviolet wavelengths which are no toriously variable The harsh environment of space coupled with the energetic solar radiation rapidly de nrarl pH a1 llrfar e and 11 Hall makes I suspect Some manner of in ight calibration is required to unambiguously separate changes in the instrument re sponse from true solar changes 7 3 5 Validation of satellite measurements The role of validation of satellitebased chemical mea surements cannot be over stressed Validation e peciall p cies using two different techniques have proved to be invaluable for understanding satellite trace species mea surements The very successful UARS validation campaign has contributed a great deal to understanding the individual UARS measurements The validation cam paigns perform two major functions First they test the ability of a satellite instrument to make a measurement by giving an independent data point to compare against Second ifthe validation measurements are performed as part of a larger coordinated campaign the validation measurements done using aircraft and groundbased mea surements can be used to link the smallscale geophysical features that they can observe with the largescale geo physical features observable from space 2323 EEIE SCIENCE F39LAN CHAPTER 7 74 EOS contributions 741 Improvements in meteorological measure ments 7411 Global limb temperature measurements The tropopause the boundary between the upper tropo sphere UT and lower stratosphere LS is critical for understanding many important processes in the atmo sphere The tropopause is de ned by a sharp change in the vertical temperature gradient taking place over a few hundred meters at most Below the tropopause the tropo sphere is a region of active vertical mixing Above the tropopause the stratosphere is very stable with little ver tical mixing The match between these dissimilar regions A f t 1 modulates r permit the exchange of mass trace gases momentum potential vorticity and energy between the two regions Unfortunately present observing systems do not observe the UTLS region with suf cient detail The NOAA operational temperature sensors are characterized by vertical resolution of the retrievals of the order of 10 12 km The detailed structure of the tropopause is much too thin to be seen by operational systems However their crosstrack scanning capability gives them the ability to observe horizontal scales of about 100 km Figure 711 pg 381 Temperature pro les with much higher vertical resolution can be obtained by observing the atmospheric limb or horizon The improvement results from the ge ometry since most of the ray path through the atmosphere is within 12 km ofthe lowest or tangent point In addi tion the atmospheric signal is seen against the cold background of space These factors can reduce the height ofthe vertical weighting functions to 34 km and the ef fective resolution to N 5 EOS limb sounders MLS and the HighResolu tion Dynamics Limb Sounder HIRDLS on the EOS Chemistry Mission CHEM will greatly improve the accuracy precision and resolution of temperature mea surements in the tropopause region HIRDLS will determine temperatures with a resolution of 115 km through a combination of a narrow 1 km vertical eld of view FOV low noise and oversampling MLS will make limb temperature measurements with a resolution of 23 km 7412 Higher horizontal resolution temperature pro files Previous limb scanners have retrieved temperatures with higher vertical resolution but because the vertical scans are made at a single azimuth relative to the orbital plane the horizontal resolution was limited to the orbital spac ing or about 25 This is suf cient to resolve only about 6 longitudinal waves However theUTLS is a region in which smallerscale waves from the troposphere are present The horizontal resolution of previous limb sound ers did not allow these smallerscale systems to be measured Figure 711 shows that the consistent scaling between vertical and horizontal scales suggests that higher horizontal resolution is required to sample geostrophic motions The gure shows that HIRDLS has the ability to observe and retrieve with a 1km vertical resolution and 4 horizontal resolution by scanning from side to side This resolution allows all horizontal waves up to N 45 to be observed with the appropriate vertical resolution Furthermore the high vertical resolu tion of HIRDLS together with the high horizontal resolution and daily observations will for the rst time provide accurate global mapping of the distribution of ozone in the lowermost stratosphere a measurement that is crucial for determining the distribution of the ux of ozone to the troposphere which in turn is crucial for un derstanding the budget of tropospheric ozone Recently atechnological innovation has been pro posed for the MLS instrument Instead of a single heterodyne receiver Microwave Monolithic Integrated Circuit MMIC arrays have been proposed at two fre quencies The array system Array MLS AMLS would allow 100km X 100km horizontal resolution tempera ture ozone N20 and water with lower power and weight This proposed system is currently being studied by NASA 742 Improvements in chemical measurements in the stratosphere EOS instruments will give signi cantly improved strato spheric chemical measurements by having better measurement precision particularly in the lower strato sphere and a morecomplete suite of collocated measurements especially chemical radicals The accu racy of the proposed instruments is close to that set down in Table 71 The major improvements in these chemical measurements are from MLS and HIRDLS These two I L r I quot AMLSare er I I I that HIRDLS will have high resolution in longitude as well as latitude discussed in the previous section while MLS will be able to make measurements in highaerosol or cloudy regions In addition highlatitude coverage will be obtained on each orbit from both HIRDLS and MLS a significant improvement from UARS which had monthly gaps in highlatitude coverage and did not sample important periods The hghrvemcal rum 7 smug m the upper m aquot a w E a a WWMWM pmcesang u I Campued thh m Mummm w Mummm 195 mu Tempende pmmn uf mm mm sphnc measurzments an mus maused mam bmmdlhmd chaise ufstmngu sputum thxeasUARS M LS wasdeaguzdpnmar m Huddle and upper mmphm EOS MLS v q UARS are surnmanzemeahle 7 2 measuredbyWS m fmnmanafClONOi 515a near sued by HIRDLS HIRDLS measlxemzn39s 1110de mm unngmmm cxouoi p m u mam the m uf m mtmgzn res1m Andaman N pm gym measlxa39nen39s whach EOS wm pzmnde This which mu m mg m OH cancemuhm hmh an an H10 5mm azmsal mg aux understanding af matasphenc hydragen chzmxslxy m 0mm ManntmnglnslxunemOMl canmbuudm EOS Chambythz Netherlands own is ahypnpemumg lusmdPSCs H10 mm W u u my culnmn quotWm a ma dznved 11er mg mum m1 m4 mm mm 7 u smmdby m mmummm Mum e mm w e m lama 1mm ma mdnsommwmmm mm Isohmanwx beondrlz mam 1mm mdmmu ma w auy dedxcned m ubhmmg mm emu n m cm my 9 shot mm mm m vemczl mm v v 1 391 Physmxsm Maan my mm Mwa sunm m dam cmbe esnmakdwnhgubd m racy m lmemnczs um man uflElV m Wm mmkxmmbehmrmm AGE m mam v a n o v m mede um styhnc and mammams m quotin H I n l h 39 n MW u a 6 I U kVVquotWWMM chemistry do not occur at this stage Later the chemical transport model will be used along with the EOS chemi cal data to produce an assimilated chemical data set The full coupling will occur through the assimilation system The observations of motion of longlived trace species can be inverted to make better estimates of stratospheric winds The forecast of temperatures from the assimila tion modeling effort will increase the accuracy of the retrieved trace gases The second effort the Pyle IDS United Kingdom uses a full GCM and chemical package The GCM and chemicalradiationtransport system will be fully linked The objectives are to examine the sensitivity of the atmo sphere to the chemicalradiativedynamical feedback systems This foreign effort consists of a full edged EOS IDS team but is not funded by NASA Z 4 6 F ull meteorological and chemical assimilation ofEOS data sets The Data Assimilation Of ce DAO at NASAG oddard Space Flight Center G SFC already provides routine sup port to the stratospheric aircraft missions planned to study stratospheric ozone Daily analyses are produced for the Stratospheric Tracers of Atmospheric Transport STRAT mission and given the duration of this mission this will evolve into the operational support of the EOS Morning Platform AMl During the aircraft deployment peri ods forecasts are produced to aid in ight planning These forecasts enhance the ability of the mission planners to target air of speci c chemical characteristics EIZDNE AND ETRATDSF HERIC CHEMISTRY 3323 The current DAO meteorological analyses have a large impact on stratospheric chemistry studies The wind elds are of suf cient quality to remove the dwamical uncertainty from trace observations This allows a high caliber examination of chemical processes a bene t that has been realized for satellite balloon and aircraft data There are active efforts of the DA0 to improve the sub tropical winds and the deep vertical motions that link the stratosphere and mesosphere Future plans call for a straightforward extension of the application of winds from the DA0 assimilation to moregeneral problems This includes stratospherictro pospheric exchange as well as broader issues of tropospheric chemistry Advanced assimilation systems will directly assimilate constituent observations First longlived tracers will be assimilated Initial studies of N20 from UARS show that assimilation can in fact pro vide veri able global information from the nonglobal UARS coverage pattern An important goal ofthe DAO constituent effort is to improve wind estimates especially in the tropics Wind inversion techniques are being ac tively investigated In addition at least two university proposals have been recently submitted to attempt to as similate aerosol observations within the DA0 system These proposals are examples of the longterm efforts to assimilate the complete chemical suite of measurements with the goal of bringing to bear the quantitative analysis of data assimilation on the internal consistency of the chemical observations ofUARS and CHEM 75 Foreign partners and other measurement sources Foreign partners are critical to the scienti c success of the global stratospheric measurements program The scale of collaborationranges from individual science teams to collaborative instruments to reciprocal ights of instru ments to mission planning The timing of the EOS CHEM mission has been structured to follow the launch of the European Space Agency s E SA s Environmental Satel lite I ENVISAT I This mission to be launched in 2000 follows the successful NASA UARS mission ENVI SAT will make many critical trace species measurements in the time period of maximum stratospheric chlorine This longterm data set UARSENVISAT CHEM will be ab solutely critical to our understanding of the role of trace species in controlling ozone in the stratosphere Other international space platforms will carry a few stratospheric instruments The French Systeme pour l Observation de la Terre SPOT satellite will carry the Polar Ozone Aerosol Measurements II POAM II aero sol and ozone measuring system The Russian MIR space station will y the Fourier Transform Spectrometer DOPI In addition to these space instruments several stratospheric aircraft campaigns are planned for the next few years eg the STRAT campaign 23234 EEIE SCIENCE F39LAN CHAPTER 7 References Aikin A C 1992 Stratospheric evidence of relativistic electron pre cipitation Planet Space Sci 40 413431 AndersonJG DW Toohey andWH ane 1991 Free radicals within the Antarctic vortex The role of CFC39s in the Antarctic ozone loss Science 251 3946 Austin J R R Garcia J M 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carbonmonoxide CO 332 CFC 314321326 CH2C12 321 CH3Cl 314 321 CHC13 321 chlorine 312327 333 CLAES 331 climate change 311 c1 315 322 DAO 333 Dobson units 312 DU 312314319 El Ni o 315 322 energetic particles 316317 319 ER2 327 foreign partners 333 greenhouse forcing 311 GSFC 324 333 H2504 316 320 HALOE 318 321 323 HCFC 321 HIRDLS 326332 HIRS 323 HO 314322 325 329 HSCT 322 IDS 331 333 interannual Variability 315316 319 IPCC 31 1 IR 315 ISAMS 331 lightning 322 manmade changes 320322 EIZDNE AND ETRATDSF HERIC CHEMISTRY 2337 measurement requiremenw 323333 METEOR3 329 validation 327 methane CH4 314 318 322 325 volcanoes 316 322 Wind 312319323324333 MLS 311324332 WMO 311316318320321324 MMIC 326328 WSR 316 modeling 317 333 MSU 323 NAD 326329 NASA 324 326 328 333 NAT 320 326329 natural changes 319320 NCAR 318 Nimbus7 311 NOAA 323324 328 NOX 314 319 322325 329 NPOESS 324 330 OCS 316 329 OH 314 321 325326 329 332 OMl 326 329332 ozone changes 312315 ozone chemistry 314315 ozone distribution 314 317 319320 ozone transport 315 UV B 311 330 precipitation 319 PSC 315316 318322 325 327 331 QBO 315 319 322 REP 317 SAGE 313 331 SAGE III 313 330332 SAM 316317 SBUV 313314 SOLSTICE 326 330331 SPOT 333 STP 312 sulfate 319320 329 sul ir 322 sul ir dioxide S02 316 319 329332 sulfuric acid 316 320 TOMS 311314 326 329331 TOVS 323324 331 trace gases 317 319 328 333 UARS 313 318321 323 326332 UT 328 UV 311 327 330331