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Atmospheric composition during twilight
Adv. Space Res. Vol. 13, No. 1, pp. (1)339—(1)342, 1993 Printed in Great Britain. All rights reserved.
0273-1177/93$15.00
Copyright © 1992 COSPAR
ATMOSPHERIC COMPOSITION DURING TWILIGHT M. J. LOpez-Gonzalez, J. J. LOpez-Moreno and R. Rodrigo Instituto de Asrrofisica de Andalucla, P.O. Box 2144, 18080 Granada, Spain
ABSTRACT A non-steady one-dimensional model for middle latitude of the Earth’s mesosphere and lower
thermosphere at equinox condition specially adapted for twilight conditions is developed to obtain the temporal dependence of the photodissociation coefficients and the concentration of the different compounds. The temporal variations obtained are used to explain the diurnal behaviour of some atmospheric 02 and OH emissions. INTRODUCTION The study of the atmospheric composition during twilight is mainly motivated by the need of knowing the behaviour of some atmospheric parameters in order to explain the diurnal variation of the main atmospheric emissions. The study of the temporal dependence of the atmospheric compounds during twilight is a complex problem because of the atmospheric changes produced by changes in solar radiation which affect the photochemistry and dynamics of the atmosphere. When one-dimensional models of the atmosphere are developed, one of the most usual simplifications is to give the same treatment to the twilight periods as to the rest of the diurnal time. This simplification, however, is only based more on considerations of computer capacity and time than on the realities of the physical situation, paying insufficient attention to the rapid and complex processes occurring during twilight and producing an unrealistic simulation of these periods. In this work a non-steady atmospheric model is developed in the altitude region of 60-220 km for middle latitudes, equinox conditions and moderate activity solar, using the latest experimental and theoretical data. This model improves an initial model /1/ where a special treatment to the twilight periods was not considered. The temporal variation of the compounds considered in the model: 0(3P), O(’D), 03, H, OH, HO2, 02, N2, H20, CO2 and CO and the photodissociation coefficients involved are obtained and these new results have been then applied, in a first approach, to the study of the diurnal variations of some of the OH and O~airgiow emissions. THEORETICAL MODEL We have used the same mathematical equations and temperature profile as in paper /1/. Molecular diffusion coefficients and a time-independent eddy diffusion coefficient profile are calculated as in /1/ following the method described in /2/. The photochemical processes considered are those proposed in /3/. The photodissociation coefficients are calculated for 02, 03, H2O and CO2 following the detailed description made in /3,4/. The lower and upper boundary, placed at 60 and 220 km respectively, are considered as in /1/. The time step for numerical integration was 15 minutes during day- and night-time. The twilight periods were divided into ten subintervals to reproduce the sudden changes in the atmosphere. These time steps are automatically reduced by a factor often when an unstable situation develops until stability is re-established. The different methods of calculation of the concentration of the compounds at different times of the day are described in detail in /3/. (1)339
M. J. López-González et at.
(1)340
RESULTS The general behaviour of this model for the different compounds agree with other more elaborate thermospheric models. The profiles obtained for the minor compounds also agree with experimental measurements. In /3/ a more detailed comparison of the obtained results with experimental measurements and other theoretical calculations is realized. In this work, we make a special emphasis on the twilight results obtained and preliminary results on some of the airglow applications are presented. In figure 1 the Jo, profile at selected twilight times is shown. The values of the photodissociation coefficients durin~twilight begin to decrease continuously at altitudes below 80 km and a negligible value is achieved even before sunset at those altitudes. At higher altitudes, the photodissociation coefficients are maintained because of the low atmospheric attenuation. During morning twilight the photodissociation coefficients begin to increase and this increase towards the maximum value is faster at higher altitudes. CO2, 1120 and 02 photodissociation coefficients show an important decrease as radiation penetrates throughout the atmosphere. This is not the case for Jo, which shows an almost constant value within the 60-220 km region. 120
.~
- . . - -
100
.
.~
. • ~
~
• . . . .
80
transport processes is evident above 80 km and neither chemistry nor photodissociation processes are capable of changing the 0-concentration significantly. Below 80 km, the concentration evolves rapidly and this corresponds to the atmospheric
-.
.
• . . . • •-. •..
60
In figure 2 the diurnal variation of 0, 03, H and OH concentrations selected is presented. As can be seen inatfigure 2a,altitudes the importance of the
.1 .
changes produced by solar radiation. In figures 2a and 2b is shown that the variation of atomic ( oxygen concentration runs parallel to that of the o3 ~S / ozone because ozone photodissociation is the main mechanism producing atomic oxygen, and, on the Fig. 1. 03 photodissociation ~oefficients at other hand, atomic oxygen recombination is the different times. Solid hue: midday. Dash- only ozone production mechanism. dotted line: sunset. Dotted lines: at intervals of 6 mm from sunset. The maximum of 0 concentra3 at 1012 96 km, and 5.6is x6 lOll cm3 at the tion at noon x lOll cm same altitude at midnight. These 10’ results are within the limits re— to’ ported by experimental measure~. ments (see /5/). The 03 concentration at the secondary maximum in the daytime is 2.2 x 108 cm3 108 at an altitude of 82 km, and 1.5 x 10, 1010 cm3 at 84 km at midnight. 10
~
.~
r
,.,
~
-~
.2.
too to LOCAL TIME (ho~r,)
LOCAL ~ME (hOu~)
Fig. 2. Diurnal variation of a) 0, b) O3~c) 11 and d) OH concentrations at selected altitudes.
Theoretical calculations predict an important increase in the 03 concentration from day to night above 70 km (/6, 7/). This prediction has been confirmed by experimental measurements. We obtain an increase in the total 03 column of about a factor of 25 above 70 km from the daytime to the nighttime value.
Figures 2c and 2d show the diurnal variation of H and OH concentrations. The main H production process is the oxidation of OH by atomic oxygen. Then during evening twilight, the atomic hydrogen concentration begins to decrease below 80 km, as does the 0 concentration. During night and below this altitude, H concentration continues decreasing although it does not disappear. During morning twilight, H concentration begins to increase as does atomic oxygen in this altitude range. Above 80 kin, both atomic hydrogen and atomic oxygen concentrations remain constant, because transport processes are predominant. The H concentrations obtained at the solar zenith angle of 102°in this model: 5.8 x 106 cm3 at 75 km, 2.3 x iO~cm3 at 80 km and less than 108 cm3 at 90 km, are in reasonable agreement with the experimental measurements of 5 x 106 cm3 at 75 km, 5 x iO~cm3 at 80 km and less
Atmospheric Composition During Twilight
(1)341
than iO~cm3 at 90 km /8/ obtained at the same solar zenith angle. The OH variation below 80 km is controlled by diurnal variations of H and 03. Above 80 km, the OH variations are directly correlated with 03 evolution because the main OH production mechanism is due to the reaction between atomic hydrogen and ozone, and H concentration is almost constant in this altitude range. AIRGLOW APLICATION Measurements of OH emissions have shown that there is a rapid decrease (or increase) in the intensity of these emissions during morning twilight (or evening twilight). Many attempts have been made to explain the photochemical mechanisms of these emissions (/6, 9, 10, 11/). 1010
120
E 10
1
a
6
12
18
24
LOCAL TIME (hours)
Fig. 3. Diurnal variation of the number of partkcles pf OH in a cm2 col~imnfor v=2 to v=6 vibrational levels. Open circles: measurements of /13/. Asterisks: measurements of /11/.
•
“E ~ 0
I
I
2x104
4x104
‘OH (phot. cm3 s’) Fig. 4. 011 emission profile. Solid line: mensurement of /15/. Dashed line: calculated.
In this paper, we have used the photocheinical scheme proposed by /11/ to calculate the OR’ emission. In figure 3 the diurnal variation of f 5~60[OH’(v))dz for v~2 to v=6 excited levels are plotted, together with the [011*] columns deduced from rocket measurements of /12/ for the same levels and those deduced from the measurement of /13/ for v=3-6 and using the Einstein coefficients recently proposed by /14/. An excellent agreement is achieved between theoretical predictions and experimental measurements considering the errors affecting both sets of data. There is a single twilight profile of OH emission reported /15/ and none has been obtained during the day. The theoretical profile obtained at twilight conditions is compared with the experimental profile for the same solar zenith angle in figure 4. The calculated profile reproduces the measured one with a reasonable qualitative and quantitative agreement bearing in mind that the use of a 0~theoretical profile is only an approximation to the real atmospheric conditions. 14 The measurements of Oz(a1~ f~io 9)emission have shown the diurnal variability of this emission. Early studies 3 the (/16/). In years, E havedayglow identifiedemission ozone photolysis as the the last mainfew source of important efforts have been developed to explain this 1 O’ ~ 10’~ twilight and nightglow emissions (/4, 17, 18/). The radiative lifetime of the 02 (a’ ‘ag) is too long (~ 3900 s) and the possible remnant daytime contribution must .j Oil be considered to calculate this twilight and early night —: emission. The processes considered at daytime con~c ditions are those proposed in twilight /4, 17/. and Thenight remnant 10 dayglow contribution during has 0 20 been calculated in detail following the same method Local time (hours) described in /4/. Figure 5 shows the diurnal variation of the calculated column density f~’~ 6o[O2(a)]dz,toFig. 5. Diurnal variation of the (0-0) gether with some experimental measu~ementsobtained band ofthe Infrared Atmospheric System at different times of the day reported by different auof 02 (the different numbers represent thors. measurements as listed in References). “
-~
M. J. López-González etal.
(1)342
-~
~1
00 80
-~
.~100 80 1000 1O~10a
10° 3s’) 0 I02(0 1 ~,) (ph. cm
I
1
10~ 2xlOa (ph. cm3s’)
O,(a s,)
Fig. 6. Infrared atmospheric system emission profiles. Solid lines: measurements. Dashed lines: theoretical reproductions. a) /26/. b) /15/. c) /12/. d) /19/.
Some profiles tamedpreliminary at differenttheoretical times of the day obare compared with the experimental ones in figure 6. It is necessary to bear in mind that we are using theoretical concentration profiles of 0 and O~to calculate the emission profile of the Infrared Atmospheric System of 02, and these profiles can only reproduce a general behaviour of the atmosphere. In order to make a more realistic comparison, it is necessary to know the real concentration profiles present when the measurements taken. As can be seen in figure 6, thewere calculated profiles agree well with the measu~edones and this confirms the appropnateness of the model results to repro~eer~~~l?ehavi~tllofdthese emissions at
Acknowledgements This research was supported by the Comisión Interministerial de Ciencia y Tecnologia under contracts ESP88-0566 and 0567. -
REFERENCES 1. R. Rodrigo, J.J. López-Moreno, M. López-Puertas, F. Moreno and A. Molina, Planet. Space Sci. 34, 723 (1986). 2. E. Battaner, J. Atmos. Terr. Phys. 37, 1155 (1975). 3. R. Rodrigo, M.J. López-Gonzé.lez and J.J. López-Moreno, Planet. Space Sci., in press (1990). 4. M.J. Lopez-Gonzales, J.J. LOpez-Moreno, M.A. López-Valverde and R. Rodrigo, Planet. Space Sci. 37, 61 (1989). 5. R. Rodrigo, J.J. LOpez-Moreno, M.J. LOpez-Gonzalez and E. Garcia-Alvarez, Planet. Space Sci. 37, 49 (1989). 6. G. Moreels, G., Megie, G., Vallance Jones, A. and Gattinger, R.L. 1977, J. Atmos. Terr. Phys. 39, 551 7. G.G. Bjarnason, S. Solomon and R.R. Garcia, J. Geophys. Res. 92, 5609 (1987). 8. D. Kita and W.E. Sharp, EOS 1~’ans.AGU63, 896 (1982). 9. E. Battaner and J.J. LOpez-Moreno, Planet. Space Sci. 27, 1421 (1979). 10. I.C. McDade and E.J. Liewellyn, J. Geophys. Re8. 92, 7643 (1987). 11. J.J. LOpes-Moreno, R. Rodrigo, F. Moreno, M. LOpez-Puertas and A. Molina, Planet. Space Sci. 35, 1029 (1987). 12. J.J. LOpez-Moreno, S. Vidal, R. Rodrigo and E.J. Llewellyn, Ann. Geophysicae 2, 61 (1984). 13. V.!. Krassovsky, N.N. Shefov and V.J. Yarin, Planet. Space Sci. 9, 883 (1962). 14. D.N. Turnbull and R.P. Lowe, Planet. Space Sci. 37, 723 (1989). 15. E.J. Liewellyn and W.F.J. Evans, in: The Radiating Atmosphere, ed. B.M. McCormac, Reidel, Dordrecht, 1971, p. 17. 16. W.F.J. Evans, D.M. liunten, E.J. Llewellyn and A. Vallance Jones, J. Geophys. Res. 73, 2885 (1968). 17. J.J. LOpez-Moreno, R. Rodrigo, F. Moreno, M. LOpez-Puertas and A. Molina, Planet. Space Sci. 36, 459 (1988). 18. I.C. McDade, E.J. Llewellyn, R.G.H. Greer and D.F. Murtagh, Planet. Space Sci. 35, 1541 (1987). 19. C.D. Howell, D.V. Michelangeli, M. Allen, Y.L. Yung and R.J. Thomas, Planet. Space Sci. 38, 529 (1990). 20. W.F.J. Evans, E.J. Llewellyn and A. Vallance Jones, 1. Geophys. Res. 77, 4899 (1972). 21. W.F.J. Evans and E.J. Llewellyn, Ann. Geophys. 26, 167 (1970). 22. H.C. Wood, W.F.J. Evans, E.J. Llewellyn and A. Valiance Jones, Can. J. Phys. 48, 862 (1970). 23. E.J. Liewellyn and G. Witt, Planet. Space Sci. 25, 165 (1977). 24. R.G.H. Greer, D.P. Murtagh, I.C. McDade, P.H.G. Dickinson, L. Thomas, D.B. Jenkins, J. Stegman, E.J. Llewellyn, G. Witt, D.J. Mackinnon and E.R. Williams, Planet. Space Sd. 34, 771 (1986). 25. R.J. Thomas and R.A. Young, .1. Geophys. Res. 86, 7389 (1981). 26. W.F.J. Evans, I.C. McDade and E.J. Llewellyn, Can. .1. Phys. 66, 941 (1988).
0273-1177/93$15.00
Copyright © 1992 COSPAR
ATMOSPHERIC COMPOSITION DURING TWILIGHT M. J. LOpez-Gonzalez, J. J. LOpez-Moreno and R. Rodrigo Instituto de Asrrofisica de Andalucla, P.O. Box 2144, 18080 Granada, Spain
ABSTRACT A non-steady one-dimensional model for middle latitude of the Earth’s mesosphere and lower
thermosphere at equinox condition specially adapted for twilight conditions is developed to obtain the temporal dependence of the photodissociation coefficients and the concentration of the different compounds. The temporal variations obtained are used to explain the diurnal behaviour of some atmospheric 02 and OH emissions. INTRODUCTION The study of the atmospheric composition during twilight is mainly motivated by the need of knowing the behaviour of some atmospheric parameters in order to explain the diurnal variation of the main atmospheric emissions. The study of the temporal dependence of the atmospheric compounds during twilight is a complex problem because of the atmospheric changes produced by changes in solar radiation which affect the photochemistry and dynamics of the atmosphere. When one-dimensional models of the atmosphere are developed, one of the most usual simplifications is to give the same treatment to the twilight periods as to the rest of the diurnal time. This simplification, however, is only based more on considerations of computer capacity and time than on the realities of the physical situation, paying insufficient attention to the rapid and complex processes occurring during twilight and producing an unrealistic simulation of these periods. In this work a non-steady atmospheric model is developed in the altitude region of 60-220 km for middle latitudes, equinox conditions and moderate activity solar, using the latest experimental and theoretical data. This model improves an initial model /1/ where a special treatment to the twilight periods was not considered. The temporal variation of the compounds considered in the model: 0(3P), O(’D), 03, H, OH, HO2, 02, N2, H20, CO2 and CO and the photodissociation coefficients involved are obtained and these new results have been then applied, in a first approach, to the study of the diurnal variations of some of the OH and O~airgiow emissions. THEORETICAL MODEL We have used the same mathematical equations and temperature profile as in paper /1/. Molecular diffusion coefficients and a time-independent eddy diffusion coefficient profile are calculated as in /1/ following the method described in /2/. The photochemical processes considered are those proposed in /3/. The photodissociation coefficients are calculated for 02, 03, H2O and CO2 following the detailed description made in /3,4/. The lower and upper boundary, placed at 60 and 220 km respectively, are considered as in /1/. The time step for numerical integration was 15 minutes during day- and night-time. The twilight periods were divided into ten subintervals to reproduce the sudden changes in the atmosphere. These time steps are automatically reduced by a factor often when an unstable situation develops until stability is re-established. The different methods of calculation of the concentration of the compounds at different times of the day are described in detail in /3/. (1)339
M. J. López-González et at.
(1)340
RESULTS The general behaviour of this model for the different compounds agree with other more elaborate thermospheric models. The profiles obtained for the minor compounds also agree with experimental measurements. In /3/ a more detailed comparison of the obtained results with experimental measurements and other theoretical calculations is realized. In this work, we make a special emphasis on the twilight results obtained and preliminary results on some of the airglow applications are presented. In figure 1 the Jo, profile at selected twilight times is shown. The values of the photodissociation coefficients durin~twilight begin to decrease continuously at altitudes below 80 km and a negligible value is achieved even before sunset at those altitudes. At higher altitudes, the photodissociation coefficients are maintained because of the low atmospheric attenuation. During morning twilight the photodissociation coefficients begin to increase and this increase towards the maximum value is faster at higher altitudes. CO2, 1120 and 02 photodissociation coefficients show an important decrease as radiation penetrates throughout the atmosphere. This is not the case for Jo, which shows an almost constant value within the 60-220 km region. 120
.~
- . . - -
100
.
.~
. • ~
~
• . . . .
80
transport processes is evident above 80 km and neither chemistry nor photodissociation processes are capable of changing the 0-concentration significantly. Below 80 km, the concentration evolves rapidly and this corresponds to the atmospheric
-.
.
• . . . • •-. •..
60
In figure 2 the diurnal variation of 0, 03, H and OH concentrations selected is presented. As can be seen inatfigure 2a,altitudes the importance of the
.1 .
changes produced by solar radiation. In figures 2a and 2b is shown that the variation of atomic ( oxygen concentration runs parallel to that of the o3 ~S / ozone because ozone photodissociation is the main mechanism producing atomic oxygen, and, on the Fig. 1. 03 photodissociation ~oefficients at other hand, atomic oxygen recombination is the different times. Solid hue: midday. Dash- only ozone production mechanism. dotted line: sunset. Dotted lines: at intervals of 6 mm from sunset. The maximum of 0 concentra3 at 1012 96 km, and 5.6is x6 lOll cm3 at the tion at noon x lOll cm same altitude at midnight. These 10’ results are within the limits re— to’ ported by experimental measure~. ments (see /5/). The 03 concentration at the secondary maximum in the daytime is 2.2 x 108 cm3 108 at an altitude of 82 km, and 1.5 x 10, 1010 cm3 at 84 km at midnight. 10
~
.~
r
,.,
~
-~
.2.
too to LOCAL TIME (ho~r,)
LOCAL ~ME (hOu~)
Fig. 2. Diurnal variation of a) 0, b) O3~c) 11 and d) OH concentrations at selected altitudes.
Theoretical calculations predict an important increase in the 03 concentration from day to night above 70 km (/6, 7/). This prediction has been confirmed by experimental measurements. We obtain an increase in the total 03 column of about a factor of 25 above 70 km from the daytime to the nighttime value.
Figures 2c and 2d show the diurnal variation of H and OH concentrations. The main H production process is the oxidation of OH by atomic oxygen. Then during evening twilight, the atomic hydrogen concentration begins to decrease below 80 km, as does the 0 concentration. During night and below this altitude, H concentration continues decreasing although it does not disappear. During morning twilight, H concentration begins to increase as does atomic oxygen in this altitude range. Above 80 kin, both atomic hydrogen and atomic oxygen concentrations remain constant, because transport processes are predominant. The H concentrations obtained at the solar zenith angle of 102°in this model: 5.8 x 106 cm3 at 75 km, 2.3 x iO~cm3 at 80 km and less than 108 cm3 at 90 km, are in reasonable agreement with the experimental measurements of 5 x 106 cm3 at 75 km, 5 x iO~cm3 at 80 km and less
Atmospheric Composition During Twilight
(1)341
than iO~cm3 at 90 km /8/ obtained at the same solar zenith angle. The OH variation below 80 km is controlled by diurnal variations of H and 03. Above 80 km, the OH variations are directly correlated with 03 evolution because the main OH production mechanism is due to the reaction between atomic hydrogen and ozone, and H concentration is almost constant in this altitude range. AIRGLOW APLICATION Measurements of OH emissions have shown that there is a rapid decrease (or increase) in the intensity of these emissions during morning twilight (or evening twilight). Many attempts have been made to explain the photochemical mechanisms of these emissions (/6, 9, 10, 11/). 1010
120
E 10
1
a
6
12
18
24
LOCAL TIME (hours)
Fig. 3. Diurnal variation of the number of partkcles pf OH in a cm2 col~imnfor v=2 to v=6 vibrational levels. Open circles: measurements of /13/. Asterisks: measurements of /11/.
•
“E ~ 0
I
I
2x104
4x104
‘OH (phot. cm3 s’) Fig. 4. 011 emission profile. Solid line: mensurement of /15/. Dashed line: calculated.
In this paper, we have used the photocheinical scheme proposed by /11/ to calculate the OR’ emission. In figure 3 the diurnal variation of f 5~60[OH’(v))dz for v~2 to v=6 excited levels are plotted, together with the [011*] columns deduced from rocket measurements of /12/ for the same levels and those deduced from the measurement of /13/ for v=3-6 and using the Einstein coefficients recently proposed by /14/. An excellent agreement is achieved between theoretical predictions and experimental measurements considering the errors affecting both sets of data. There is a single twilight profile of OH emission reported /15/ and none has been obtained during the day. The theoretical profile obtained at twilight conditions is compared with the experimental profile for the same solar zenith angle in figure 4. The calculated profile reproduces the measured one with a reasonable qualitative and quantitative agreement bearing in mind that the use of a 0~theoretical profile is only an approximation to the real atmospheric conditions. 14 The measurements of Oz(a1~ f~io 9)emission have shown the diurnal variability of this emission. Early studies 3 the (/16/). In years, E havedayglow identifiedemission ozone photolysis as the the last mainfew source of important efforts have been developed to explain this 1 O’ ~ 10’~ twilight and nightglow emissions (/4, 17, 18/). The radiative lifetime of the 02 (a’ ‘ag) is too long (~ 3900 s) and the possible remnant daytime contribution must .j Oil be considered to calculate this twilight and early night —: emission. The processes considered at daytime con~c ditions are those proposed in twilight /4, 17/. and Thenight remnant 10 dayglow contribution during has 0 20 been calculated in detail following the same method Local time (hours) described in /4/. Figure 5 shows the diurnal variation of the calculated column density f~’~ 6o[O2(a)]dz,toFig. 5. Diurnal variation of the (0-0) gether with some experimental measu~ementsobtained band ofthe Infrared Atmospheric System at different times of the day reported by different auof 02 (the different numbers represent thors. measurements as listed in References). “
-~
M. J. López-González etal.
(1)342
-~
~1
00 80
-~
.~100 80 1000 1O~10a
10° 3s’) 0 I02(0 1 ~,) (ph. cm
I
1
10~ 2xlOa (ph. cm3s’)
O,(a s,)
Fig. 6. Infrared atmospheric system emission profiles. Solid lines: measurements. Dashed lines: theoretical reproductions. a) /26/. b) /15/. c) /12/. d) /19/.
Some profiles tamedpreliminary at differenttheoretical times of the day obare compared with the experimental ones in figure 6. It is necessary to bear in mind that we are using theoretical concentration profiles of 0 and O~to calculate the emission profile of the Infrared Atmospheric System of 02, and these profiles can only reproduce a general behaviour of the atmosphere. In order to make a more realistic comparison, it is necessary to know the real concentration profiles present when the measurements taken. As can be seen in figure 6, thewere calculated profiles agree well with the measu~edones and this confirms the appropnateness of the model results to repro~eer~~~l?ehavi~tllofdthese emissions at
Acknowledgements This research was supported by the Comisión Interministerial de Ciencia y Tecnologia under contracts ESP88-0566 and 0567. -
REFERENCES 1. R. Rodrigo, J.J. López-Moreno, M. López-Puertas, F. Moreno and A. Molina, Planet. Space Sci. 34, 723 (1986). 2. E. Battaner, J. Atmos. Terr. Phys. 37, 1155 (1975). 3. R. Rodrigo, M.J. López-Gonzé.lez and J.J. López-Moreno, Planet. Space Sci., in press (1990). 4. M.J. Lopez-Gonzales, J.J. LOpez-Moreno, M.A. López-Valverde and R. Rodrigo, Planet. Space Sci. 37, 61 (1989). 5. R. Rodrigo, J.J. LOpez-Moreno, M.J. LOpez-Gonzalez and E. Garcia-Alvarez, Planet. Space Sci. 37, 49 (1989). 6. G. Moreels, G., Megie, G., Vallance Jones, A. and Gattinger, R.L. 1977, J. Atmos. Terr. Phys. 39, 551 7. G.G. Bjarnason, S. Solomon and R.R. Garcia, J. Geophys. Res. 92, 5609 (1987). 8. D. Kita and W.E. Sharp, EOS 1~’ans.AGU63, 896 (1982). 9. E. Battaner and J.J. LOpez-Moreno, Planet. Space Sci. 27, 1421 (1979). 10. I.C. McDade and E.J. Liewellyn, J. Geophys. Re8. 92, 7643 (1987). 11. J.J. LOpes-Moreno, R. Rodrigo, F. Moreno, M. LOpez-Puertas and A. Molina, Planet. Space Sci. 35, 1029 (1987). 12. J.J. LOpez-Moreno, S. Vidal, R. Rodrigo and E.J. Llewellyn, Ann. Geophysicae 2, 61 (1984). 13. V.!. Krassovsky, N.N. Shefov and V.J. Yarin, Planet. Space Sci. 9, 883 (1962). 14. D.N. Turnbull and R.P. Lowe, Planet. Space Sci. 37, 723 (1989). 15. E.J. Liewellyn and W.F.J. Evans, in: The Radiating Atmosphere, ed. B.M. McCormac, Reidel, Dordrecht, 1971, p. 17. 16. W.F.J. Evans, D.M. liunten, E.J. Llewellyn and A. Vallance Jones, J. Geophys. Res. 73, 2885 (1968). 17. J.J. LOpez-Moreno, R. Rodrigo, F. Moreno, M. LOpez-Puertas and A. Molina, Planet. Space Sci. 36, 459 (1988). 18. I.C. McDade, E.J. Llewellyn, R.G.H. Greer and D.F. Murtagh, Planet. Space Sci. 35, 1541 (1987). 19. C.D. Howell, D.V. Michelangeli, M. Allen, Y.L. Yung and R.J. Thomas, Planet. Space Sci. 38, 529 (1990). 20. W.F.J. Evans, E.J. Llewellyn and A. Vallance Jones, 1. Geophys. Res. 77, 4899 (1972). 21. W.F.J. Evans and E.J. Llewellyn, Ann. Geophys. 26, 167 (1970). 22. H.C. Wood, W.F.J. Evans, E.J. Llewellyn and A. Valiance Jones, Can. J. Phys. 48, 862 (1970). 23. E.J. Liewellyn and G. Witt, Planet. Space Sci. 25, 165 (1977). 24. R.G.H. Greer, D.P. Murtagh, I.C. McDade, P.H.G. Dickinson, L. Thomas, D.B. Jenkins, J. Stegman, E.J. Llewellyn, G. Witt, D.J. Mackinnon and E.R. Williams, Planet. Space Sd. 34, 771 (1986). 25. R.J. Thomas and R.A. Young, .1. Geophys. Res. 86, 7389 (1981). 26. W.F.J. Evans, I.C. McDade and E.J. Llewellyn, Can. .1. Phys. 66, 941 (1988).