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4-15-1994

New Sources for the Hot Oxygen Geocorona

P. G. Richards University of Alabama - Huntsville

Michael P. Hickey Ph.D. Embry-Riddle Aeronautical University, [email protected]

D. G. Torr University of Alabama - Huntsville

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Scholarly Commons Citation Geophysical Research Letters, vol. 21, no. 8, pages 657-660, April 15, 1994.

This Article is brought to you for free and open access by Scholarly Commons. It has been accepted for inclusion in Publications by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. GEOPHYSICAL RESEARCH LETTERS, VOL. 21, NO. 8, PAGES 657-660, APRIL 15, 1994

New sources for the hot oxygen geocorona

P. G. Richards,M.P. Hickey,and D. G. Torr Centerfor SpacePlasma and Aeronomic Research, The University of Alabamain Huntsville

Abstract. Thispaper investigates new sourcesof thermospheric experimentalevidence was suppliedby Hedin [1989]. He in- nonthermal (hot) oxygendue to exothermicreactions involving ferredhot oxygen densities of 1 to 3xl0 n at 1100km for low to numerousminor (ion and neutral) and roetastablespecies. moderatesolar activitiesby comparingthe satellite drag based Numericalcalculat,ions are performedfor low latitude,daytime, (Jacchia)model and the massspectrometer based (MSIS) model. winter conditions,with moderatelyhigh solar activity and low More recently,Cotton et al. [1993] have inferreda substantial magneticactivity. Under these conditionswe find that the hot O populationfrom a soundingrocket measurement of the quenchingof roetastablespecies are a significantsource of hot ultravioletatomic oxygen dayglow. oxygen,with kinetic energyproduction rates a factorof ten The only sourcesof hot O that were consideredby Rohrbaugh + + higherthan those due to previously considered O2 and NO + andNisbet [1973] were electron recombination ofO 2 and NO +. dissociative recombination reactions. Some of the most However,there are a largenumber of otherpossible sources of significantnew sourcesof hot oxygenare reactionsinvolving hot oxygenatoms that have not been consideredpreviously quenchingof O+(2D), O(1D), N(2D), O+(2P) and vibrationally [Table 1]. Most of these reactionswere not consideredby excitedN2 by atomic oxygen. Rohrbaughand Nisbet [1973] becausethey involveroetastable specieswhose importance was only establishedlater, mainly throughthe AtmosphereExplorer program [Torr and Torr, Introduction 1982].Metastable species contain electronic energy that canbe transferredto translationalenergy in quenchingprocesses..For The possibilityof a hot atomic oxygengeocorona was first example,the roetastable N(2D) which has an electronicenergy discussedtheoretically by Rohrbaughand Nisbet [1973] who of 2.4 eV is producedvery efficiently in the thermosphere calculatedthe flux of energeticatoms resulting from the throughdirect photodissociationand numerouschemical reac- dissociativerecombination ofO2 +and NO + in the F regionofthe tionsand is quenchedefficiently by atomic oxygen. When N(2D) Earth'sionosphere. They found that the hot atomscan ascend to is quenched,the electronicenergy is made availableto the altitudes of several thousand kilometers and can travel horizon- translationalenergy of the two atomswhich would then both be tally to distancesof the orderof theEarth's radius. hot. The existenceof a substantialhot oxygengeocorona is of importanceto our understandingof the Earth'satmosphere for severalreasons including the maintenanceof the nighttime Model ionosphere,the escapeflux of He, andenergetic ion populations The hot oxygenproduction rates are calculatedusing the Field in the plasmasphere.The hot O could help to explain the Line InterhemisphericPlasma (FLIP) transportmodel [Richards maintenanceof the nighttimeionosphere by increasingthe rate of conversionof plasmaspheric14+ into O+. Currentmodel et al., 1994]. This model solvesthe coupledtime dependent energy,momentum, and continuityequations for the majorions calculations,which include ionosphere-plasmaspherecoupling, (O+, I-I+ andHe+), and photoelectron transport equations, from indicatethat the flux from the plasmasphereis not sufficientto 80 km in one hemisphere,along a field line to 80 km in the maintain the ionosphericdensities at the observedlevels other hemisphere.The concentrationsof the major neutral [Richardset al., 1994]. speciesare providedby the MSIS-86 model [Hedin, 1987]. The Anotherpossible effect of the hot O geocoronacould be to mainoutputs of the FLIP modelinclude ion densities(O +, enhancethe escapeof light atoms from the atmosphereby O+(nS),O+(2D), O+(2P), I-I+, He,+ N+, NO,N + 2 +,N 2 +*),neutral increasingthe populationof the highenergy tail of the light ion 1 1 3 + distributionthrough collisional energy exchange. Thus, hot O densities(N(nS), N(2D), N(2P), NO, O(D), O(S), N2(A Zu ), couldhelp to explainthe well knowndiscrepancy between the N2*),electron andion temperatures andflow velocities, thepho- toelectronflux, and a large number of emissions.A recent He outgassingrate and the Jeansescape flux. Finally, the summaryof the FLIP modelis providedby Torr et al. [1990]. existenceof a significanthot O populationin the plasmasphere coupledwith chargeexchange with H+ couldenhance the We have identifieda total of twentysix possiblesources of hot populationofplasmaspheric O+ and also the heating of plasmas- oxygen.They are listed in Table 1 and are taken from Rees [1989].Note that reactions1, 2 and 3 havebeen previously ex- phericions. mined as a sourceof hot oxygenby Rohrbaughand Nisbet Experimentalevidence for the hot oxygengeocorona has been [1973].In thispaper we makeno attemptto decidethe partition- presentedby Yeeet al. [1980]who made twilight measurements ofthe O+(2P) 7320 A emission.Their measurements indicated a ing of energyamongst the productsof the reactions.This parti- hotoxygen density of up to 106cm '3 at 550km altitude. Further tioningcan be complexdepending on the pathwaysfor the reac- tions.In reactionsinvolving atomic species of similarmasses (O and N) it is probablyreasonable to assumethat the electronic Copyright1994 by the AmericanGeophysical.Union. energyis sharedequally by the resultingproducts, whereas in reactionsinvolving molecules, the energypartitioning is compli- Paper number 94GL00561 catedby possibleelectronic and vibrationalexcitation of the 0094-8534/94/94GL-00561503.00 molecule.Forexample, reaction 10(O+(2D) + N 2 ---) O + N2+) 657 658 RICHARDS ET AL.' HOT OXYGEN GEOCORONA

Table 1. Potentialsources of hotoxygen and their exothermicities (AE)

No. Reaction ReactionRate (cm 3 s'l) • (ev)

1 NO+ + e--> N + O 4.3x10'7(T_/300)4 (22%) 2.75 2 NO++ e --> N(2D) +O 4.3x10'7(T?300)4 (78%) 0.38 3 0 ++ e -->0 + 0 Torret al. (1990) 4.42 2.38 45 o•O2++ N(2tD)O(D) -->N(4S)O + O+ O -7x108x1042'13 1.96 6 O + O+(2P)--> O + + O 4xl0 '1ø 5.00 7 O + O+(2D) --> O + + O 5xl0 42 3.31 8 N(2D)+ O+-->N + + O 5x1041 1.46 1.55 9 02+O+--> +2 02+ + O + 2.1x1041{Tn+2Ti/3x300}-ø'763 10 N_+O (D) --> N 2 +O 8x10'10 1.33 11 OltD)+N2--> O+ N2 2.0x104•exp(107.8T) 1.96 12 O+ + H -->O + H+ 2.2x10'tt Tø'5 kT. 13 N(2D)+02 --> NO + O 6x1042 3.7• 14 N(2p)+ O -->N + O 1.7x104• 3.58 15 NO + N -->N_ + O 3.4xl 04• 3.25 16 N + O_--> N(• + O 4.4xl0'12exp(-3220/T) 1.385 17 N++ (•2 '-> NO+ +O 2xl04o 6.67 18 O(D)+O+ 2 2--•O•+ +O 7xl0-10 4.865 19 O+(2P)+N 2 --> N; +O 4.8xl0'10 3.02 20 O(1D)+02 ---> 02 + O 2.9x10'11exp(67.5/T) 1.96 21 O + + N --->NO + + O 1.2xl040 4.2 22 N•.+ N(2D) -->N_ +O 7xl 0'1• 5.63 23- 26 N2 (v=i) +O --> l•2(v'=i-1) +O McNealetal. (1974) 0.3v mayresult in the excitation ofthe N2+(A) state [Omholt, 1957], modelwas nm for an initialperiod of 24 hoursprior to thistime, in whichcase most of the energywill be radiated.Alternatively, in orderto reducedependence on initial conditions. thereaction may produce N2+(X) in vibrational levels up to v = The hot O numberdensity production rates derived from the set 5. Spectroscopicmeasurements made on the ATLAS 1 mission + of chemicalreactions given in Table 1 areplotted as a function indicatesignificant production ofN 2 (X), with little or no pro- of altitudein Figure1. For clarityof presentation,the results ductionofN_+(A) (Torr et al., 1993).In thiscase, O quenchinghave been separatedinto two groups,the first containing of the vibrationallevels may lead to a significantsource of hot reactions1 to 11 and the secondcontaining reactions 13 to 26 O. However,the chemistryof vibrationallyexcited N + hasnot (reaction12 did not contributeto the productionof hotO for the yetbeen fully quantified. Reaction 12(O + + H • O+ I•I +) would results considered here). The hot O numberdensity production onlybe a significantsource ofhot O forT i >>Tn, which only oc- rateis dominated byquenching ofN2*(v=l and 2) byatomic cursabove ~ 500km where O + densitiesare low. It isnot likely oxygen(reactions 23 and 24) at all but the highestaltitudes to be a significantsource of hotO onEarth. Reaction 12 is only (Figure lb). At the highestaltitudes, the hot oxygennumber a candidatefor oxygenion temperaturesexceeding 3000 K. Re- densityproduction rates are predominantlyproduced by (in actions23 to 26 correspond toN 2 vibrationallevels (v) ranging decreasing order of importance)reactions 10, 5, 7 and4 (Figure from 1 to 4, respectively.In this studywe are primarilyinter- la), with smallerproduction rates being due to the dissociative estedin comparingthe new sources of hotoxygen with the pre- recombination reactions 2 and 3. viouslyknown sources (reactions 1, 2 and 3) in orderto demon- While the numberdensity production rates are usefulindicators stratethe potentialimportance of thesenew sources.We em- of whichsources may be of significanceto thehot O population, phasizethat it is the localproduction of hotoxygen that is calcu- the kinetic energyproduction rates are of greaterinterest latedhere. The final distributionof hot oxygenatoms will de- becausethey are a directmeasure of theavailable kinetic energy pendon collisionsand transport, and is beyondthe scopeof this for the productoxygen atom. These kinetic energy production paper.Transport will becomeimportant above 300 - 400 km and rates (Figure 2) were obtainedby multiplyingthe number will beprimarily responsible for populating the exosphere. densityproduction rate by the exothermicityfor eachreaction in Table 1. In general,the energyimparted to the atomicoxygen Results will onlybe half of the totalenergy. The results shownin Figure 2a demonstratethat dissociative The FLIP model was nm for different seasons and different recombinationofNO + (reaction 1)and 02 + (reactions2 and 3) levelsof solaractivity. It was discoveredthat the new sourcesof are not the most significantsources of hot oxygenat high hotoxygen favored conditions ofhigh solar activity (F•0.? = 200) altitudes.Atomic oxygen quenching of O+(2D) (reaction 7) is a duringwinter (day 1). It is theseresults that we havechosen to largesource of hot oxygenat high altitudes,but a minorsource describehere. A moredetailed analysis involving seasonal and at low altitudes.At highaltitudes, the kineticenergy production solarcyclical variations of thesesources is thesubject of a paper rate due to O+(2D)quenching exceeds that due to the inpreparation. A lowlevel of magnetic activity (Ap = 12),a low dissociativerecombination reactions by a factor of eight. latitude(23øN), and a localtime of 12.9 hourswere used. The Quenchingof the roetastable states N(2D) (reactions 4), O(•D) RICHARDS ET AL.' HOT OXYGEN GEOCORONA 659

600

600...... , ...... ' ' [ ...... ' ...... ' -- OeN(•p) NO',.+© .-. NeNO ii iiiiii .... NO+eGii i [i ill t ii i it itt I --. iN.O•i i ii iii [ •1 • N10 O•+• . • -- o• 500 F '"•• • --- O+N•D} - 500 '--' o.•) ['• .... ' X•' • • .... O,O•2P) --- o• D)

400• e'"'•""..?•}•?...N '•.'-x•• ', ...... 02,0 ß • 400•••. '-' --'-• -.• ', '-'.. '--'.....•N,'(V•)

'-- .... • ....O• D)+N2 __ L•--•...•••.. .(• • -... '',• '•.•ß.. -.. sooI• • • N • •..•..•.'--::.h.•.•N•, S00 -,, , ß .. [ 7/ % ,.-., -- ...... 0o 10• 10• 10a 10• 0o 10• 10• 10a •4 PRODUCTION RATE (cm'3s'l) PRODUCTION RATE (cm-3s-1) Figure1. HotO numberdensity production rates for reactions (a) 1to 11,and (b) 12to 26.

(reaction5) andO+(2P) (reaction 6) byatomic oxygen are also Conclusion largesources of hot oxygenat highaltitudes. The factthat reactions1 to 7 all produceatoms of similarmass means that the We havefound that the quenchingof metastablespecies is a partitioningofenergy between the two reaction products will be significantsource of hot oxygenfor the exosphere.For the similar for these reactions. Therefore, the kinetic energy geophysicalconditions employed here (winter,high solar productionrates due to these reactions can be compared directly. activity),the kineticenergy production rates due to someof thesenew sources exceeded, by a factorof ten, thosedue to the Reaction10 is potentiallya very large source of hotoxygen at + highaltitudes, although the uncertaintyassociated with the previouslyconsidered 02 and NO + dissociativerecombination energypartitioning must not be overlooked.Quenching of reactions.Some of the most significantnew sourcesof hot O+(2D)by0 2 (reaction 18),and quenching ofN2*(v=l to3) by oxygenfound in this studyare due to reactionsinvolving atomicoxygen (reactions 23, 24, and25) (Figure2b) aresources quenchingof O+(2D), O(•D), N(2D), O+(2P) and vibrationally of hotoxygen that are comparable to those due to reactions1, 2 excitedN2 by atomic oxygen. These additional sources ofhot and3 at highaltitudes. We notethat there is someuncertainty oxygen may help to explainthe maintenance of the nighttime regardingthe values of someof thereaction rates, particularly ionosphere, the escapeflux of helium,and energeticion thosefor reactions5, 6 and 7. populationsin theplasmasphere.

600 600

500 500

400 400

300 300

i i i i I illl 20010o 20010o 101 102 103 104 KINETIC ENERGY PRODUCTION RATE (Ev cm-3s-•) KINETIC ENERGY PRODUCTION RATE (Ev cm-35-1) Figure2. HotO kineticenergy production rates for reactions (a) 1to 11, and (b) 12 to 26. 660 RICHARDS ET AL.: HOT OXYGEN GEOCORONA

A detailed studyis now under way to ascertainthe diurnal, Omholt, A., The red and near-infra-redauroral spectrum,J. Atmos. seasonal,and solarcyclical variations of the main sourcesof hot Ten,. Phys., 10, 320, 1957. O. Furtherwork is alsoneeded to determinethe partitioningof Rees, M. H., Physics and chemistryof the upper atmosphere, energybetween the productsof the reactionsthat may produce CambridgeUniversity Press, 1989. Richards, P. G., D. G. Torr, B. W. Reinischand R. R. Gamache,F2 energetic0 atoms. peak electrondensity at MillstoneHill: Comparisonof theoryand measurementat solarmaximum, J. Geophys.Res., in press,1994. Acknowledgments.This work was supportedby NSF grantsATM- Rohrbaugh,R. P. and J. S. Nisbet, Effect of oxygenatoms on neutral 9224988 and ATM-9018165, and NASA grant NAGW-996 at the densitymodels, J. Geophys.Res., 78, 6768, 1973. Universityof Alabamain Huntsville. Torr, M. R. and D. G. Torr, The role of roetastablespecies in the thermosphere,Rev. of Geophys.,20, 91, 1982. References Torr, M. R., D. G. Torr, P. G. Richardsand S. P. Yung, Mid- and low-latitudemodel of thermosphericemissions 1. O+(2P) 7320 A Cotton,D. M., G. R. Gladstoneand S. Chakrabarti,Sounding rocket andN, (2P) 3371A, J. Geophys.Res., 95, 21,147,1990. observationof a hot oxygen geocorona,J. Geophys.Res., 98, Torr,M. •., D. G.Torr, T. Chang,P. G. Richards, T. W. Baldridge,J.

21,651, 1993.ß K. Owens, H. Dougani, C. Fellows,W. Swiit, S. Yung and J. Hedin, A. E., MSIS-86 thermospheremodel, J. Geophys.Res., 92, Hladky,The first negative bands of N + in thedayglow from the 4649, 1987. ATLAS1shuttle mission, Geophys. Re2s.,Lett., 20, 523, 1993. Hedin, A.E., Hot oxygen geocoronaas inferred from neutral Yee, J-H., J. W. Meriwetherand P. B. Hays, Detectionof a coronaof exosphericmodels and mass spectrometermeasurements, J. fast oxygenatoms during solar maximum,J. Geophys.Res., 85, Geophys.Res., 94, 5523, 1989. 3396, 1980. McNeal, R. J., M. E. Whitson, Jr., and G. R. Cool Temperature dependenceof the quenchingof vibrationallyexcited nitrogen by P. G. Richards,M.P. Hickey, and D. G. Torr, Centerfor Space atomicoxygen, J. Geophys.Res., 79, 1527, 1974. Plasma and Aeronomic Research,The University of Alabama in Newton, G. P., J. C. G. Walker and P. H. E. Meijer, Vibrationally Huntsville,Huntsville, AL 35899. (e-mail:Richards•cs.uah.edu) excited nitrogen in stable auroral red arcs and its effect on ionosphericrecombination, J. Geophys.Res., 79, 3807, 1974. (Received:January 24, 1994;accepted: February 16, 1994)