This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low latitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2+ and NO+ dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O+(²D), O(¹D), N(²D), O+(²P) and vibrationally excited N2 by atomic oxygen

Hickey, Michael P., Ph.D.

Richards, P. G.

Torr, D. G.

English

Embry-Riddle Aeronautical University

Publications 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, hicke0b5@erau.edu D. G. Torr University of Alabama - Huntsville Follow this and additional works at: https://commons.erau.edu/publication  Part of the Atmospheric Sciences Commons 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 commons@erau.edu. 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 Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville Abstract. This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and roetastable species. Numerical calculat,ions are performed for low latitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of roetastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten + higher than those due to previously considered O 2 and NO + dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O+(2D), O(1D), N(2D), O+(2P) and vibrationally excited N 2 by atomic oxygen. Introduction The possibility of a hot atomic oxygen geocorona was first discussed theoretically by Rohrbaugh and Nisbet [1973] who calculated the flux of energetic atoms resulting from the dissociative recombination of O2 +and NO + in the F region ofthe Earth's ionosphere. They found that the hot atoms can ascend to altitudes of several thousand kilometers and can travel horizon- tally to distances of the order of the Earth's radius. The existence of a substantial hot oxygen geocorona is of importance to our understanding of the Earth's atmosphere for several reasons including the maintenance of the nighttime ionosphere, the escape flux of He, and energetic ion populations in the plasmasphere. The hot O could help to explain the maintenance of the nighttime ionosphere by increasing the rate of conversion of plasmaspheric 14 + into O +. Current model calculations, which include ionosphere-plasmasphere coupling, indicate that the flux from the plasmasphere is not sufficient o maintain the ionospheric densities at the observed levels [Richards et al., 1994]. Another possible effect of the hot O geocorona could be to enhance the escape of light atoms from the atmosphere by increasing the population of the high energy tail of the light ion distribution through collisional energy exchange. Thus, hot O could help to explain the well known discrepancy between the He outgassing rate and the Jeans escape flux. Finally, the existence of a significant hot O population in the plasmasphere coupled with charge exchange with H + could enhance the population f plasmaspheric O + and also the heating of plasmas- pheric ions. Experimental evidence for the hot oxygen geocorona has been presented by Yee et al. [1980] who made twilight measurements of the O+(2P) 7320 A emission. Their measurements i dicated a hot oxygen density of up to 106 cm '3 at 550 km altitude. Further Copyright 1994 by the American Geophysical.Union. Paper number 94GL00561 0094-8534/94/94GL-00561503.00 experimental evidence was supplied by Hedin [1989]. He in- ferred hot oxygen densities of1 to 3xl 0 n at 1100 km for low to moderate solar activities by comparing the satellite drag based (Jacchia) model and the mass spectrometer based (MSIS) model. More recently, Cotton et al. [1993] have inferred a substantial hot O population from a sounding rocket measurement of the ultraviolet atomic oxygen dayglow. The only sources of hot O that were considered by Rohrbaugh + and Nisbet [ 1973] were lectron recombination of O 2 and NO +. However, there are a large number of other possible sources of hot oxygen atoms that have not been considered previously [Table 1]. Most of these reactions were not considered by Rohrbaugh and Nisbet [1973] because they involve roetastable species whose importance was only established later, mainly through the Atmosphere Explorer program [Torr and Torr, 1982]. Metastable species contain electronic energy that can be transferred to translational energy in quenching processes..For example, the roetastable N(2D) which has an electronic energy of 2.4 eV is produced very efficiently in the thermosphere through direct photodissociation and numerous chemical reac- tions and is quenched fficiently by atomic oxygen. When N(2D) is quenched, the electronic energy is made available to the translational energy of the two atoms which would then both be hot. Model The hot oxygen production rates are calculated using the Field Line Interhemispheric Plasma (FLIP) transport model [Richards et al., 1994]. This model solves the coupled time dependent energy, momentum, and continuity equations for the major ions (O +, I-I + and He+), and photoelectron transport equations, from 80 km in one hemisphere, along a field line to 80 km in the other hemisphere. The concentrations of the major neutral species are provided by the MSIS-86 model [Hedin, 1987]. The main outputs of the FLIP model include ion densities (O +, O+(nS), O+(2D), O+(2P), I-I +, He, N +, + + +* + NO,N ,N ),neutral 2 2 1 1 3 + densities (N(nS), N(2D), N(2P), NO, O(D), O(S), N2(A Zu ), N2*), electron and ion temperatures and flow velocities, the pho- toelectron flux, and a large number of emissions. A recent summary of the FLIP model is provided by Torr et al. [1990]. We have identified a total of twenty six possible sources of hot oxygen. They are listed in Table 1 and are taken from Rees [1989]. Note that reactions 1, 2 and 3 have been previously ex- mined as a source of hot oxygen by Rohrbaugh and Nisbet [1973]. In this paper we make no attempt o decide the partition- ing of energy amongst he products of the reactions. This parti- tioning can be complex depending on the pathways for the reac- tions. In reactions involving atomic species of similar masses (O and N) it is probably reasonable to assume that the electronic energy is shared equally by the resulting products, whereas in reactions involving molecules, the energy partitioning is compli- cated by possible electronic and vibrational excitation of the molecule. Forexample, r action 10 (O+(2D) + N 2 ---) O + N2 +) 657 658 RICHARDS ET AL.' HOT OXYGEN GEOCORONA Table 1. Potential sources of hot oxygen and their exothermicities (AE) No. Reaction Reaction Rate (cm 3s 'l) 1 NO + + e --> N + O 4.3x10'7(T_/300) 4 (22%) 2 NO ++ e --> N(2D) + O 4.3x10'7(T?300) 4 (78%) 3 0 + + e --> 0 + 0 Torr et al. (1990) 4 •O2++ N(2tD) --> N(4S) + O -7x10 ' 3 5 o O(D) --> O + O 8x1042 6 O + O+(2P) --> O + + O 4xl 0 '1ø 7 O + O +(2D) --> O + + O 5xl 0 42 8 N(2D) + O+--> N + + O 5x1041 9 02+ O+--> 02 + + O 2.1x1041{Tn+2Ti/3x300}-ø'763 +2 + 10 N_+ O (D) --> N 2 + O 8x10 '10 11 OltD) + N2--> O + N2 2.0x104•exp(107.8 T) 12 O + + H --> O + H + 2.2x10 'tt T ø'5 13 N(2D) + 02 --> NO + O 6x1042 14 N(2p) + O --> N + O 1.7x104• 15 NO + N --> N_ + O 3.4xl 04• 16 N + O_ --> N(• + O 4.4xl 0'12exp(-3220/T) 17 N+  (•2 '-> NO+ + O 2xl 04o + 2 + 0-10 18 O(D)+O 2--•O• +O 7xl 19 O+(2P) + N 2 --> N; + O 4.8xl 0 '10 20 O(1D) + 02 ---> 02 + O 2.9x10'11exp(67.5/T) 21 O + + N ---> NO + + O 1.2xl 040 22 N•. + N(2D) --> N_ + O 0 '1• 7xl 23 -26 N 2 (v=i) +O --> l•2(v'=i-1) + O McNeal t l. (1974) • (ev) 2.75 0.38 4.42 2.38 1.96 5.00 3.31 1.46 1.55 1.33 1.96 kT. 3.7• 3.58 3.25 1.385 6.67 4.865 3.02 1.96 4.2 5.63 0.3v may result in the excitation f the N2+(A) state [Omholt, 1957], in which case most of the energy will be radiated. Alternatively, the reaction may produce N2+(X) in vibrational levels up to v = 5. Spectroscopic measurements made on the ATLAS 1 mission + indicate significant production of N 2 (X), with little or no pro- duction ofN_+(A) (Torr et al., 1993). In this case, O quenching of the vibrational levels may lead to a significant source of hot O. However, the chemistry of vibrationally excited N + has not yet been fully quantified. Reaction 12 (O + + H • O + I•I +) would only be a significant source ofhot O for T i >> Tn, which only oc- curs above ~ 500 km where O + densities are low. It is not likely to be a significant source of hot O on Earth. Reaction 12 is only a candidate for oxygen ion temperatures exceeding 3000 K. Re- actions 23 to 26 correspond to N2 vibrational levels (v) ranging from 1 to 4, respectively. In this study we are primarily inter- ested in comparing the new sources of hot oxygen with the pre- viously known sources (reactions 1, 2 and 3) in order to demon- strate the potential importance of these new sources. We em- phasize that it is the local production of hot oxygen that is calcu- lated here. The final distribution of hot oxygen atoms will de- pend on collisions and transport, and is beyond the scope of this paper. Transport will become important above 300 - 400 km and will be primarily responsible for populating the exosphere. Results The FLIP model was nm for different seasons and different levels of solar activity. It was discovered that the new sources of hot oxygen favored conditions f high solar activity (F•0.? = 200) during winter (day 1). It is these results that we have chosen to describe here. A more detailed analysis involving seasonal and solar cyclical variations of these sources i the subject of a paper in preparation. A low level of magnetic activity (Ap = 12), a low latitude (23øN), and a local time of 12.9 hours were used. The model was nm for an initial period of 24 hours prior to this time, in order to reduce dependence on initial conditions. The hot O number density production rates derived from the set of chemical reactions given in Table 1 are plotted as a function of altitude in Figure 1. For clarity of presentation, the results have been separated into two groups, the first containing reactions 1 to 11 and the second containing reactions 13 to 26 (reaction 12 did not contribute to the production of hot O for the results considered here). The hot O number density production rate is dominated by quenching of N2*(v=l and 2) by atomic oxygen (reactions 23 and 24) at all but the highest altitudes (Figure lb). At the highest altitudes, the hot oxygen number density production rates are predominantly produced by (in decreasing order of importance) reactions 10, 5, 7 and 4 (Figure la), with smaller production rates being due to the dissociative recombination reactions 2 and 3. While the number density production rates are useful indicators of which sources may be of significance tothe hot O population, the kinetic energy production rates are of greater interest because they are a direct measure of the available kinetic energy for the product oxygen atom. These kinetic energy production rates (Figure 2) were obtained by multiplying the number density production rate by the exothermicity for each reaction in Table 1. In general, the energy imparted to the atomic oxygen will only be half of the total energy. The results shown in Figure 2a demonstrate that dissociative + recombination of NO+ (reaction 1) and 02 (reactions 2 and 3) are not the most significant sources of hot oxygen at high altitudes. Atomic oxygen quenching of O+(2D) (reaction 7) is a large source of hot oxygen at high altitudes, but a minor source at low altitudes. At high altitudes, the kinetic energy production rate due to O+(2D) quenching exceeds that due to the dissociative recombination reactions by a factor of eight. Quenching of the roetastable states N(2D) (reactions 4),O(•D) RICHARDS ET AL.' HOT OXYGEN GEOCORONA 659 600 i i i iiiii i i [ iill t i i i i t itt I ii i i i iii 600 ........ , ........ ' ' [ ........ ' ........ ' -- .... OeN(•p) NO',.+© .-. NeNO .... NO+eG --. N.O• [ •1 • N10 O• +• . • -- o• 500 F '"•• • --- O+N•D} - 500 '--' o.•) ['• .... ' X•' • • .... O,O•2P) -- - o• D) • ..... • •""..?•}•?... •• ...... 02,0 •••. • -. ', '.. '--' •N,'(V•) 400 e' ' N ' .'-x ', ß 400 '-' --'- • '- • .... O• D)+N2 __ . (• -. ' • ß.. '-- L•--•...•••.. • .. '•.• - . .... ', I • N •..•..•. soo • • • • '--::.h.•.•N•, S00 -,, , ß .. [ 7/ % ,.-., -- ...... 0o 10• 10 • 10a 10• 0o 10• 10 • 10a PRODUCTION RATE (cm'3s 'l) PRODUCTION RATE (cm-3s -1) Figure 1. Hot O number density production rates for reactions (a)1 to 11, and (b) 12 to 26. •4 (reaction 5)and O+(2P) (reaction 6)by atomic oxygen are also large sources of hot oxygen at high altitudes. The fact that reactions 1 to 7 all produce atoms of similar mass means that the partitioning of energy between the two reaction products will be similar for these reactions. Therefore, the kinetic energy production rates due to these reactions can be compared directly. Reaction 10 is potentially a very large source of hot oxygen at high altitudes, although t e uncertainty associated with the energy partitioning must not be overlooked. Quenching ofO+(2D) by 02 (reaction 18),and quenching of N2*(v=l to 3) by atomic oxygen (reactions 23, 24, and 25) (Figure 2b) are sources of hot oxygen that are comparable to those due to reactions 1,2 and 3 at high altitudes. We note that there is some uncertainty regarding the values of some of the reaction rates, particularly those for reactions 5, 6 and 7. Conclusion We have found that the quenching of metastable species is a significant source of hot oxygen for the exosphere. For the geophysical conditions employed here (winter, high solar activity), the kinetic energy production rates due to some of these new sources exceeded, by a factor of ten, those due to the + previously considered 02 and NO + dissociative recombination reactions. Some of the most significant new sources of hot oxygen found in this study are due to reactions involving quenching of O+(2D), O(•D), N(2D), O+(2P) and vibrationally excited N 2by atomic oxygen. These additional sources of hot oxygen may help to explain the maintenance of the nighttime ionosphere, the escape flux of helium, and energetic ion populations inthe plasmasphere. 600 500 400 300 20010o 600 500 400 300 20010o i i i i I illl 101 102 103 104 KINETIC ENERGY PRODUCTION RATE (Ev cm-3s-•) KINETIC ENERGY PRODUCTION RATE (Ev cm-35 -1) Figure 2. Hot O kinetic energy production rates for reactions (a)1 to 11, and (b) 12 to 26. 660 RICHARDS ET AL.: HOT OXYGEN GEOCORONA A detailed study is now under way to ascertain the diurnal, seasonal, and solar cyclical variations of the main sources of hot O. Further work is also needed to determine the partitioning of energy between the products of the reactions that may produce energetic 0 atoms. Acknowledgments. This work was supported by NSF grants ATM- 9224988 and ATM-9018165, and NASA grant NAGW-996 at the University of Alabama in Huntsville. References Cotton, D. M., G. R. Gladstone and S. Chakrabarti, Sounding rocket observation of a hot oxygen geocorona, J. Geophys. Res., 98, 21,651, 1993. ß Hedin, A. E., MSIS-86 thermosphere model, J. Geophys. Res., 92, 4649, 1987. Hedin, A.E., Hot oxygen geocorona as inferred from neutral exospheric models and mass spectrometer measurements, J. Geophys. Res., 94, 5523, 1989. McNeal, R. J., M. E. Whitson, Jr., and G. R. Cool Temperature dependence of the quenching of vibrationally excited nitrogen by atomic oxygen, J. Geophys. Res., 79, 1527, 1974. Newton, G. P., J. C. G. Walker and P. H. E. Meijer, Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination, J. Geophys. Res., 79, 3807, 1974. Omholt, A., The red and near-infra-red auroral spectrum, J. Atmos. Ten,. Phys., 10, 320, 1957. Rees, M. H., Physics and chemistry of the upper atmosphere, Cambridge University Press, 1989. Richards, P. G., D. G. Torr, B. W. Reinisch and R. R. Gamache, F2 peak electron density at Millstone Hill: Comparison of theory and measurement at solar maximum, J. Geophys. Res., in press, 1994. Rohrbaugh, R. P. and J. S. Nisbet, Effect of oxygen atoms on neutral density models, J. Geophys. Res., 78, 6768, 1973. Torr, M. R. and D. G. Torr, The role of roetastable species in the thermosphere, Rev. of Geophys., 20, 91, 1982. Torr, M. R., D. G. Torr, P. G. Richards and S. P. Yung, Mid- and low-latitude model of thermospheric missions 1. O+(2P) 7320 A and N, (2P) 3371 A, J. Geophys. Res., 95, 21,147, 1990. Torr, M. •., D. G. Torr, T. Chang, P. G. Richards, T. W. Baldridge, J. K. Owens, H. Dougani, C. Fellows, W. Swiit, S. Yung and J. Hladky, The first negative bands of N + in the dayglow from the ATLAS 1 shuttle mission, Geophys. Re2s., Lett., 20, 523, 1993. Yee, J-H., J. W. Meriwether and P. B. Hays, Detection of a corona of fast oxygen atoms during solar maximum, J. Geophys. Res., 85, 3396, 1980. P. G. Richards, M.P. Hickey, and D. G. Torr, Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, Huntsville, AL 35899. (e-mail: Richards•cs.uah.edu) (Received: January 24, 1994; accepted: February 16, 1994) 

New Sources for the Hot Oxygen Geocorona

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New Sources for the Hot Oxygen Geocorona

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