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The effect of variations in temperature and nitric oxide density on ion-clustering in the mesopause region during winter anomaly
Jourd
0021-9169/78/1101-1147$02.00/O
of Armospheric and TerrestrialPhysics. Vol. 40. pi. 1147-1152
OPergamon
Press
Ltd.. 1978.Printedin Northern
Ireland
The effect of variations in temperature and nitric oxide density on ionclusteringin the mesopauseregion during winter anomaly* D. K. ~HA~~Arn+t,
P. CHAKRABARTY~
Uppsala Ionospheric Observatory, S-755 90 Uppsala-1,
Sweden
and G. Wn-I Institute of Meteorology, University of Stockholm, Arrhenius Laboratory, P. 0. Box 10405, Stockholm, (Received
Sweden
10 July 1977: in revised form 1 April 1978)
Abatraet-Rocket measurements have shown that changes occur in the D-region electron density N, positive ion composition and mesopause temperature T during the days of anomalous winter absorption. In this paper. we have examined these changes on the basis of a detailed positive ion chemical scheme. This scheme is first made to satisfy the normal D-region features. When this scheme is applied to winter anomaly, it is seem that the increase of N is more sensitive to the increase of [NO] than to the increase of T, and the factor by which N increases, [NO] has to be increased by almost the same factor. The observed increase of [30+$[32+] ratio by about an order at 80-85 km altitude region is also explainable by an increase of NO density. However, to explain the observed decrease of [48’]/[30+] by about an order at 80-85 km region, an increase of T by about 50 K is necessary. The increase of T also shifts the water cluster population from higher hydrates to lower hydrates and this, coupled with an increase of [NO], lowers the height of the transition from hydrated to molecular positive ions from about 82.5 km to about 75 km 1. UWRODUCTION
A number of rocket campaigns have been conducted in the past by various groups to study the changes that occur in different parameters of the D-region of the ionosphere during winter anomaly. It has been found that electron density N increases between 75 to 90 km region when absorption exceeds 20dB (WILLIAMS, 1977; GEUER and SECHRIST, 1971). The extent of this increase depends on the severity of the event. In an extreme case, as on 29 November 1974 when absorption was greater than 50 dB, WILLIAMS (1977) found the increase of electron density by a factor as large as 100 around 82 km. The increase of temperature in the mesopause region has also been observed by different amount ( GELLER and SECHRIST, 1971; THRANE, private communication). The first measurement of positive ion composition on a winter day of excessive absorption was made by ZB~NDEN et al. 1975). They found that 37’ was the major ion below 77 km in both up and down legs. The 55’ ion was not observed in the downleg, but in the upleg its concentration was found much less than that of 37’. A recent measurement by MEISTER et * Presented at COSPAR symposium held in Tel Aviv, Israel in June 1977. t Present address: Physical Research Laboratory, Ahmedabad 9, India.
al. (1978) however, shows that below 76 km, 55’ and 73’ are equally abundant. Their measurements also show an increase of 30’132’ ratio by a factor of about 100 and a decrease of 48’130’ ratio by a factor of about 10 during winter anomaly from normal time in 80-85 km altitude region. Similar results are obtained by ARNOLD and KRANKOWSKY (1977). The transition height of hydrated protons to molecular ions goes down during winter anomaly from quiet daytime level. The amount by which this goes down appears to depend on the severity of the event. Bern group (MEISTER et al., 1978; ZBINDEN et al., 1975) observed the transition height around 76.5 km while Heidelberg group (ARNOLD and KRANKOWSKY, 1977) in the extreme case of 29 November 1974 found the transition height at about 70 km. Both the groups pointed out that above this altitude the profile of N practically coincided with the profile of NO’ ions. It is now believed that the winter anomaly is not due to the increase in the electron production rate by particle precipitation of solar origin. And hence to explain the increase of N, several authors (WILLIAMS, 1977) have suggested that winter anomaly absorption arises as a result of greatly enhanced NO concentration in the D-region heights. In this paper, we have examined these changes on the basis of a detailed positive ion chemical scheme. This scheme is first made to reproduce the
1147
D. K.
1148
CHAKRABARTY et al.
quiet daytime D-region feature (CHAKRABARTYet al., 1978a). Next we have increased the temperature and NO concentration by different amounts and studied whether the observed features mentioned above could be reproduced. 2.
MElll0DoLoGY
It has been shown by CHAKRABARTY et al. (1978a) that the presently known detailed positive ion chemical scheme as such is not able to explain the observed D-region features satisfactorily. The following modifications are necessary: (a) Reactions analogous to NO’ to NO’. H20, for the conversion of NO+*H20 to NO’*(H,O), and NO+S(H~O)~ ions.
Ion
clustering
H+~(H,O),+H+*(H,O),,~X~H’~(H,O).+,. It may be mentioned that some of the modifications have also been proposed earlier by several authors (HEIMERL and VANDERHOFF, 1974; JOHNSEN et Cd., 1975). The presently known positive ion chemical scheme with the above modifications is shown in Fig. 1 along with the rates, the references of which are available from CHAKRABARTY et al. (1978a) and FERGUSON (1973). The coefficients of reactions and the temperature dependence of (a) and (b) mentioned above have also been shown in Fig. 1.
scheme
Rl = R9 = R15 = 2.5 x 10-29(200/T)2 [CO,] [NJ R2 = R10 = R16 = 2.0 x 1O-31(3OO/T)4.4 [N,] [NJ R3 = 1.1 x 10-8(300/T)4~4exp(-2125/~ [NJ R4 = R12 = R18 = 1.0 x 1O-9 [CO,] R5=R13=R19=1.0x10-9~H,01 R6 = R14 = R20 = 1.0x 1O-9 [H;Oj R7=1.0xlO-‘“TN LI+0 91
R8=7~10-‘~[I_i] L LRll = R17 = lOR3 R21= 3.3 x lo-” [H,O] R22 = R23 = lOR7
(b) Fast path for converting 02+ to 02+.H20. (c) Formation of hydrated protons through steps like
R24 = 4.4 x lo-” [NO] R25 = 1.0x lo-l7 [NJ R26 = 2.4 x 10-“0(300/T)3.2 [OJ (O,] R27=3.0xlO-“‘[O] R28 = 2.2 x lo-’ [H,O] R29 = 0.6 (photodetachment) R30 = 1.9x 1O-9 [H,O] R31= 3.C x lo-” [H,O] R32 = 3.2 x 1O-9 [H,O] Ul = 2.5 x 1O-31 [N,+O,] 2(300/T)4.4 U2 = 1.0 x 1O-9 [H,O]
Fig. 1. Schematic diagram of positive ion reactions with their rates.
The effect of temperature and nitric oxide density on ion-clustering in the mesopause region BS=lOOxB, F2 = 8 x 10-32(300/T)4.4[Mp F,=F,=F,=F, F,=lOxF,
For B and F the following relations have been used (CHAKRABARTY et al., 1978a) B3 = 5 x 10-3[M](300/Z94~4 exp (-5000/T) B, = 1O-4 x B3 B, = lo-* x B3 B,=SOxB,
-
--
lo4
-
The continuity equations of all the ions shown in Fig. 1 are framed on the basis of reactions and their
-Normal WA -Wintuwmmaly
Obsrved Theorrticol
100
10’
102
Im rntii Obwrnd
t=l
1149
Lwrl ,
Normal-95 km Wintoranomaly -77-70
km
T - Constant
Obsmd increase dNbyX)-llX
(b)
(a)
Non0rma1ous p-1
Fig. 2. Increase of electron density ratio: (a) when normal time temperature is increased by 50, 100 and 150 K; (b) when normal time nitric oxide density is increased by factors of 5, 10 and 50. Change of H+.(H,O),J(NO++O,+) ratio; (c) when normal time temperature is increased by 50 K; (d) when normal time nitric oxide density is increased by factors of 5 and 10. Observed: (e) 48+/30’ ratio and (f) 30’/32’ ratio (from ZSP~DENet al., 1975; msn~ et al., 1978) for normal and winter anomaly conditions along with theoretical values when normal time temperature and nitric oxide density are increased by 50 K and by a factor of 10 respectively.
1150
D. K. CHAKRAEZARTY
rates also shown in the same figure. These equations are solved simultaneously by a computer in the manner described earlier (CHAKFUBAFWY et al., 1977). The photo-ionisation rate of NO by Lyman alpha has been calculated using revised NO density measured by MEIRA (1971) and Lyman alpha intensity as 4.2 rates of ergs cm -*s-’ A-‘. Ion pair production O,(‘A,) by solar radiation in 1025-1118A have been taken from HUFFMANN et al. (1971) and the electron ion pair production rates by X-rays less than 1008, have been calculated in the manner described in CHAKRABARTY and CHAKRABARTY (1973). For neutral atmospheric density we have used the model given in CIRA (1972). The concentrations of minor constituents 0, H, H,O and 0, have been taken from HE~STVEDT (1968) and of CO, is deduced assuming a constant mixing ratio of 3 x 10e4. The values of different a,‘s-the ionelectron recombination rates are taken from SWIDER and NARCISI (1975). In this scheme we now increase the temperatures by 50, 100 and 150K and NO density by a factor of 5, 10 and 50 from MEIRA (1971) values. The results thus obtained are shown in Fig. 2, the discussion of which are given below.
3. RESULTS AND
DISCUSSIONS
In Figs 2(a, b) we have shown the effect of increase of T and NO densities on electron densities. It is seen that even when the temperature is increased by 150 K, as an extreme possibility, the increase of electron density in 80-85 km range is by a factor of about only 3 when the observed values are much higher. It is thus clear that the increase of temperature alone is not sufficient to explain the observations. On the other hand, the effect of the increase of NO density is much pronounced. An increase of NO density by a factor as large as 50 can increase the electron density by a factor of about 10. In Figs 2(c, d) are shown H’.(H,O),,/(NO’+ 02+), hereafter referred to as f, for different temperature and NO densities. It is seen that while for normal case f = 1 level lies around 85 km, when the temperature increases by about 50 K and the NO density increase by a factor of 10, the f = 1 level goes down below 80 km. It is also to be noted that the increase of temperature lowers the f= 1 level much more quickly than the increase of NO density. The question may arise whether a change of temperature is indeed necessary to account for the features of winter anomaly. This point will be clear from Figs. 2(e, f) where we have plotted [48’]/[30’]
etnl.
and [30’]/[32’]. It can be seen that an increase of [NO] by a factor of 10 decreases the [48’]/[30’] marginally and increases [3O’y[32’] by more than an order of magnitude. On the other hand, an of temperature by 50K decreases increase [48’]/[30+] by about an order of magnitude and increases [30’]/[32’] marginally. Thus we see that to explain the observed decrease of [48’]/[30’] and increase of [30’]/[32’] we need increase of both temperature and nitric oxide density. The change of T and NO density is probably not the same below 80 km as it is above this altitude. This is also apparent from the recent measurements of MEISTER et al. (1978) who got equal abundance of 55’ and 73’ during an anomalous winter day as is observed in quiet daytime indicating thereby that the temperature did not change at and below the transition height during this flight. It may be mentioned that during winter the temperatures are much less stable and may experience substantial deviations from the mean value by as much as *50 K and also there is temperature inversionthe base of the inversion varying from 80 km to as low as 65 km and the inversion being greater for winter than summer (SCHMIDLJN, 1976). In Fig. 3 we have given a theoretical model of electron and ion densities for a winter anomaly condition when the temperature and nitric oxide density have been increased by 50 K and by a factor of 5 respectively from those of normal values throughout the height range of 80-90 km. In view of the unpredictable situation regarding the variation of temperature (SCHMIDLIN, 1976) and long life-time of nitric oxide, we have not considered any change
-
Observed ---- Thaontical
3
Ions ond electrons
lo3
(cni3)
Fig. 3. A theoretical model of electron and ion densities for a winter anomaly condition when normal time temperature and nitric oxide density have been increased by 50K and by a factor of 5 respectively. The measured values of ZBINDEN et al.(1975) are also shown.
The effect of temperature and nitric oxide density on ion-clustering in the mesopause region of these two parameters below 80 km. For the sake of comparison, we have also plotted in the same figure the measured values of ZBINDEN et al. (1975). Good agreement between theoretical and observed profiles of N, 30+ and 32’ is noticed. For 37’, agreement is good only above 78 km. Below this height, a rapid increasing trend in the experimentally measured profile of 37’ indicates some unreliability of data as this is not noticed in the subsequent observation by the same group using the same technique (MEISTER et al., 1978). Disagreement is also noticed between the observed and theoretical profiles of 48”. However, certain basic features are seen to be reproduced. Besides increase of electron density, which is obvious since NO density has been increased, the transition level of predominance of hydrated ions to molecular ions is lowered to about 76 km from the normal level of about 83 km. It is also seen that above 76 km the profile of 30’ closely follows the profile of N as observed. The increase of temperature at the mesopause region makes the concentration of lower hydrate, 37’ greater than that of 55’ and 73’ as experimentally found.
4. CONCLUSION
Changes in N and positive ion composition have been observed during winter anomaly in the height range of 75-90 km. These have been explained on
1151
the basis of detailed positive ion chemical scheme. It has been found that to reproduce properly the observed distribution of N and positive ion composition, both increases of temperature and NO density are necessary. The increase of temperature has been observed by several groups. An increase of temperature when incorporated in an ionneutral chemical scheme in which the transport mechanism has been included, increases the concentration of NO. As for example, an increase of temperature by about 75 K when introduced in our ion-neutral chemical scheme (see CHAKRARAR~ et al., 1978b) increases the NO density around 85 km by a factor of about 5. To understand the extent of transport process on winter anomaly, the behaviour of minor constituents such as odd nitrogen. oxygen and hydrogen which are highly sensitive to transport parameter could be studied by airglow emission. In this direction satellite limb scanning observations should be of great help in obtaining a global picture of mesospheric weather.
Acknowledgements-We are grateful to Dr. E. KOPP for making available to us the preliminary results of his recent flights at Wallops Island. We thank Dr. R. R. BURKE for his critical comments and useful suggestions. We also thank Drs R. BOSTR~M and H. DER~LOM for their interest in this work. Two of the authors D. K. C. and G. W.. acknowledge the Swedish Board for Space Activities, Stockholm and the third P. C., acknowledges the Swedish Institute, Stockholm for financial support.
REFERENCES
Dynamical and Chemical Coupling of the Neutral and Ionized Atmosphere, p. 93, Reidel.
ARNOLD F. and KRANKOWSKY D
1977
CHAKRABARTY D. K. and CHAKRABARTY P. CHAKRABARTY D. K. CHAKRABARTY P. and BJORN L. CHAKRABARTY P., CHAKRABARTY D. K. and B&RN L.
1973 1977
J. atmos. terr. Phys. 39, 57
1978b
J. atmos. terr. Phys. (in press)
CHAKRABARTY D. K.. CHAKRABARTT P. and WI-IT G.
1978
.I. atmos. terr. Phys. 40, 437.
CIRA
1972
FERGUSON E. E. GELLER M. A. and SECHRISTC. F., Jr HEIMERL J. M. and VANDERHOFFJ. A. HESSTVEDTE. HUFFMANN R. E., PAULSEN D. E., LARRABEE J. C. and CAIRNS R. B. JOHNSENR., HUANG C. M. and BIONDI M. A. MEIRA L. G.. Jr
1973 1971 i974 1968 1971
COSPAR International Reference Atmosphere (Compiled by COSPAR working group IV). Atomic Data and Nuclear Data Tables. 12, 159.
MEITI-ERJ., EBERHARDT P., HERRMANN U., KOPP E., HIDALGO M. A. and &CHRIST C. F. JR. SCHMIDI-INF. J.
Ind. J. Radio Space Phys. 2. 21 1
J. atmos. terr. Phys. 33, 1027. J. Chem. Phys. 60, 4362. Geophys. Norvegica 27, 1. J. geophys. Res. 76, 1028.
1975
J. Chem. Phys. 63, 3374.
1971 1978
J. geophys. Res. 76, 202.
1976
Geophys. Res. Lett. 3, 173.
Space Research XVIII, p. 155, Pergamon
Press.
1152 SWIDER W. and NARCISI WILLIAMS E. R.
D. K. CHAKRABARTY
R. S.
P. A., HIDALGO M. A., EBERHAFCDT P. and GEISS J.
ZBINDEN
1975 1977 1975
Reference is also made to the following unpublished material: THRANEE. V. 1977
et&. J. geophys. Res. 80, 665. Space Research XVII, p. 279. Pergamon &ss. Planet. Space Sci. 23, 1621,
Private communication
0021-9169/78/1101-1147$02.00/O
of Armospheric and TerrestrialPhysics. Vol. 40. pi. 1147-1152
OPergamon
Press
Ltd.. 1978.Printedin Northern
Ireland
The effect of variations in temperature and nitric oxide density on ionclusteringin the mesopauseregion during winter anomaly* D. K. ~HA~~Arn+t,
P. CHAKRABARTY~
Uppsala Ionospheric Observatory, S-755 90 Uppsala-1,
Sweden
and G. Wn-I Institute of Meteorology, University of Stockholm, Arrhenius Laboratory, P. 0. Box 10405, Stockholm, (Received
Sweden
10 July 1977: in revised form 1 April 1978)
Abatraet-Rocket measurements have shown that changes occur in the D-region electron density N, positive ion composition and mesopause temperature T during the days of anomalous winter absorption. In this paper. we have examined these changes on the basis of a detailed positive ion chemical scheme. This scheme is first made to satisfy the normal D-region features. When this scheme is applied to winter anomaly, it is seem that the increase of N is more sensitive to the increase of [NO] than to the increase of T, and the factor by which N increases, [NO] has to be increased by almost the same factor. The observed increase of [30+$[32+] ratio by about an order at 80-85 km altitude region is also explainable by an increase of NO density. However, to explain the observed decrease of [48’]/[30+] by about an order at 80-85 km region, an increase of T by about 50 K is necessary. The increase of T also shifts the water cluster population from higher hydrates to lower hydrates and this, coupled with an increase of [NO], lowers the height of the transition from hydrated to molecular positive ions from about 82.5 km to about 75 km 1. UWRODUCTION
A number of rocket campaigns have been conducted in the past by various groups to study the changes that occur in different parameters of the D-region of the ionosphere during winter anomaly. It has been found that electron density N increases between 75 to 90 km region when absorption exceeds 20dB (WILLIAMS, 1977; GEUER and SECHRIST, 1971). The extent of this increase depends on the severity of the event. In an extreme case, as on 29 November 1974 when absorption was greater than 50 dB, WILLIAMS (1977) found the increase of electron density by a factor as large as 100 around 82 km. The increase of temperature in the mesopause region has also been observed by different amount ( GELLER and SECHRIST, 1971; THRANE, private communication). The first measurement of positive ion composition on a winter day of excessive absorption was made by ZB~NDEN et al. 1975). They found that 37’ was the major ion below 77 km in both up and down legs. The 55’ ion was not observed in the downleg, but in the upleg its concentration was found much less than that of 37’. A recent measurement by MEISTER et * Presented at COSPAR symposium held in Tel Aviv, Israel in June 1977. t Present address: Physical Research Laboratory, Ahmedabad 9, India.
al. (1978) however, shows that below 76 km, 55’ and 73’ are equally abundant. Their measurements also show an increase of 30’132’ ratio by a factor of about 100 and a decrease of 48’130’ ratio by a factor of about 10 during winter anomaly from normal time in 80-85 km altitude region. Similar results are obtained by ARNOLD and KRANKOWSKY (1977). The transition height of hydrated protons to molecular ions goes down during winter anomaly from quiet daytime level. The amount by which this goes down appears to depend on the severity of the event. Bern group (MEISTER et al., 1978; ZBINDEN et al., 1975) observed the transition height around 76.5 km while Heidelberg group (ARNOLD and KRANKOWSKY, 1977) in the extreme case of 29 November 1974 found the transition height at about 70 km. Both the groups pointed out that above this altitude the profile of N practically coincided with the profile of NO’ ions. It is now believed that the winter anomaly is not due to the increase in the electron production rate by particle precipitation of solar origin. And hence to explain the increase of N, several authors (WILLIAMS, 1977) have suggested that winter anomaly absorption arises as a result of greatly enhanced NO concentration in the D-region heights. In this paper, we have examined these changes on the basis of a detailed positive ion chemical scheme. This scheme is first made to reproduce the
1147
D. K.
1148
CHAKRABARTY et al.
quiet daytime D-region feature (CHAKRABARTYet al., 1978a). Next we have increased the temperature and NO concentration by different amounts and studied whether the observed features mentioned above could be reproduced. 2.
MElll0DoLoGY
It has been shown by CHAKRABARTY et al. (1978a) that the presently known detailed positive ion chemical scheme as such is not able to explain the observed D-region features satisfactorily. The following modifications are necessary: (a) Reactions analogous to NO’ to NO’. H20, for the conversion of NO+*H20 to NO’*(H,O), and NO+S(H~O)~ ions.
Ion
clustering
H+~(H,O),+H+*(H,O),,~X~H’~(H,O).+,. It may be mentioned that some of the modifications have also been proposed earlier by several authors (HEIMERL and VANDERHOFF, 1974; JOHNSEN et Cd., 1975). The presently known positive ion chemical scheme with the above modifications is shown in Fig. 1 along with the rates, the references of which are available from CHAKRABARTY et al. (1978a) and FERGUSON (1973). The coefficients of reactions and the temperature dependence of (a) and (b) mentioned above have also been shown in Fig. 1.
scheme
Rl = R9 = R15 = 2.5 x 10-29(200/T)2 [CO,] [NJ R2 = R10 = R16 = 2.0 x 1O-31(3OO/T)4.4 [N,] [NJ R3 = 1.1 x 10-8(300/T)4~4exp(-2125/~ [NJ R4 = R12 = R18 = 1.0 x 1O-9 [CO,] R5=R13=R19=1.0x10-9~H,01 R6 = R14 = R20 = 1.0x 1O-9 [H;Oj R7=1.0xlO-‘“TN LI+0 91
R8=7~10-‘~[I_i] L LRll = R17 = lOR3 R21= 3.3 x lo-” [H,O] R22 = R23 = lOR7
(b) Fast path for converting 02+ to 02+.H20. (c) Formation of hydrated protons through steps like
R24 = 4.4 x lo-” [NO] R25 = 1.0x lo-l7 [NJ R26 = 2.4 x 10-“0(300/T)3.2 [OJ (O,] R27=3.0xlO-“‘[O] R28 = 2.2 x lo-’ [H,O] R29 = 0.6 (photodetachment) R30 = 1.9x 1O-9 [H,O] R31= 3.C x lo-” [H,O] R32 = 3.2 x 1O-9 [H,O] Ul = 2.5 x 1O-31 [N,+O,] 2(300/T)4.4 U2 = 1.0 x 1O-9 [H,O]
Fig. 1. Schematic diagram of positive ion reactions with their rates.
The effect of temperature and nitric oxide density on ion-clustering in the mesopause region BS=lOOxB, F2 = 8 x 10-32(300/T)4.4[Mp F,=F,=F,=F, F,=lOxF,
For B and F the following relations have been used (CHAKRABARTY et al., 1978a) B3 = 5 x 10-3[M](300/Z94~4 exp (-5000/T) B, = 1O-4 x B3 B, = lo-* x B3 B,=SOxB,
-
--
lo4
-
The continuity equations of all the ions shown in Fig. 1 are framed on the basis of reactions and their
-Normal WA -Wintuwmmaly
Obsrved Theorrticol
100
10’
102
Im rntii Obwrnd
t=l
1149
Lwrl ,
Normal-95 km Wintoranomaly -77-70
km
T - Constant
Obsmd increase dNbyX)-llX
(b)
(a)
Non0rma1ous p-1
Fig. 2. Increase of electron density ratio: (a) when normal time temperature is increased by 50, 100 and 150 K; (b) when normal time nitric oxide density is increased by factors of 5, 10 and 50. Change of H+.(H,O),J(NO++O,+) ratio; (c) when normal time temperature is increased by 50 K; (d) when normal time nitric oxide density is increased by factors of 5 and 10. Observed: (e) 48+/30’ ratio and (f) 30’/32’ ratio (from ZSP~DENet al., 1975; msn~ et al., 1978) for normal and winter anomaly conditions along with theoretical values when normal time temperature and nitric oxide density are increased by 50 K and by a factor of 10 respectively.
1150
D. K. CHAKRAEZARTY
rates also shown in the same figure. These equations are solved simultaneously by a computer in the manner described earlier (CHAKFUBAFWY et al., 1977). The photo-ionisation rate of NO by Lyman alpha has been calculated using revised NO density measured by MEIRA (1971) and Lyman alpha intensity as 4.2 rates of ergs cm -*s-’ A-‘. Ion pair production O,(‘A,) by solar radiation in 1025-1118A have been taken from HUFFMANN et al. (1971) and the electron ion pair production rates by X-rays less than 1008, have been calculated in the manner described in CHAKRABARTY and CHAKRABARTY (1973). For neutral atmospheric density we have used the model given in CIRA (1972). The concentrations of minor constituents 0, H, H,O and 0, have been taken from HE~STVEDT (1968) and of CO, is deduced assuming a constant mixing ratio of 3 x 10e4. The values of different a,‘s-the ionelectron recombination rates are taken from SWIDER and NARCISI (1975). In this scheme we now increase the temperatures by 50, 100 and 150K and NO density by a factor of 5, 10 and 50 from MEIRA (1971) values. The results thus obtained are shown in Fig. 2, the discussion of which are given below.
3. RESULTS AND
DISCUSSIONS
In Figs 2(a, b) we have shown the effect of increase of T and NO densities on electron densities. It is seen that even when the temperature is increased by 150 K, as an extreme possibility, the increase of electron density in 80-85 km range is by a factor of about only 3 when the observed values are much higher. It is thus clear that the increase of temperature alone is not sufficient to explain the observations. On the other hand, the effect of the increase of NO density is much pronounced. An increase of NO density by a factor as large as 50 can increase the electron density by a factor of about 10. In Figs 2(c, d) are shown H’.(H,O),,/(NO’+ 02+), hereafter referred to as f, for different temperature and NO densities. It is seen that while for normal case f = 1 level lies around 85 km, when the temperature increases by about 50 K and the NO density increase by a factor of 10, the f = 1 level goes down below 80 km. It is also to be noted that the increase of temperature lowers the f= 1 level much more quickly than the increase of NO density. The question may arise whether a change of temperature is indeed necessary to account for the features of winter anomaly. This point will be clear from Figs. 2(e, f) where we have plotted [48’]/[30’]
etnl.
and [30’]/[32’]. It can be seen that an increase of [NO] by a factor of 10 decreases the [48’]/[30’] marginally and increases [3O’y[32’] by more than an order of magnitude. On the other hand, an of temperature by 50K decreases increase [48’]/[30+] by about an order of magnitude and increases [30’]/[32’] marginally. Thus we see that to explain the observed decrease of [48’]/[30’] and increase of [30’]/[32’] we need increase of both temperature and nitric oxide density. The change of T and NO density is probably not the same below 80 km as it is above this altitude. This is also apparent from the recent measurements of MEISTER et al. (1978) who got equal abundance of 55’ and 73’ during an anomalous winter day as is observed in quiet daytime indicating thereby that the temperature did not change at and below the transition height during this flight. It may be mentioned that during winter the temperatures are much less stable and may experience substantial deviations from the mean value by as much as *50 K and also there is temperature inversionthe base of the inversion varying from 80 km to as low as 65 km and the inversion being greater for winter than summer (SCHMIDLJN, 1976). In Fig. 3 we have given a theoretical model of electron and ion densities for a winter anomaly condition when the temperature and nitric oxide density have been increased by 50 K and by a factor of 5 respectively from those of normal values throughout the height range of 80-90 km. In view of the unpredictable situation regarding the variation of temperature (SCHMIDLIN, 1976) and long life-time of nitric oxide, we have not considered any change
-
Observed ---- Thaontical
3
Ions ond electrons
lo3
(cni3)
Fig. 3. A theoretical model of electron and ion densities for a winter anomaly condition when normal time temperature and nitric oxide density have been increased by 50K and by a factor of 5 respectively. The measured values of ZBINDEN et al.(1975) are also shown.
The effect of temperature and nitric oxide density on ion-clustering in the mesopause region of these two parameters below 80 km. For the sake of comparison, we have also plotted in the same figure the measured values of ZBINDEN et al. (1975). Good agreement between theoretical and observed profiles of N, 30+ and 32’ is noticed. For 37’, agreement is good only above 78 km. Below this height, a rapid increasing trend in the experimentally measured profile of 37’ indicates some unreliability of data as this is not noticed in the subsequent observation by the same group using the same technique (MEISTER et al., 1978). Disagreement is also noticed between the observed and theoretical profiles of 48”. However, certain basic features are seen to be reproduced. Besides increase of electron density, which is obvious since NO density has been increased, the transition level of predominance of hydrated ions to molecular ions is lowered to about 76 km from the normal level of about 83 km. It is also seen that above 76 km the profile of 30’ closely follows the profile of N as observed. The increase of temperature at the mesopause region makes the concentration of lower hydrate, 37’ greater than that of 55’ and 73’ as experimentally found.
4. CONCLUSION
Changes in N and positive ion composition have been observed during winter anomaly in the height range of 75-90 km. These have been explained on
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the basis of detailed positive ion chemical scheme. It has been found that to reproduce properly the observed distribution of N and positive ion composition, both increases of temperature and NO density are necessary. The increase of temperature has been observed by several groups. An increase of temperature when incorporated in an ionneutral chemical scheme in which the transport mechanism has been included, increases the concentration of NO. As for example, an increase of temperature by about 75 K when introduced in our ion-neutral chemical scheme (see CHAKRARAR~ et al., 1978b) increases the NO density around 85 km by a factor of about 5. To understand the extent of transport process on winter anomaly, the behaviour of minor constituents such as odd nitrogen. oxygen and hydrogen which are highly sensitive to transport parameter could be studied by airglow emission. In this direction satellite limb scanning observations should be of great help in obtaining a global picture of mesospheric weather.
Acknowledgements-We are grateful to Dr. E. KOPP for making available to us the preliminary results of his recent flights at Wallops Island. We thank Dr. R. R. BURKE for his critical comments and useful suggestions. We also thank Drs R. BOSTR~M and H. DER~LOM for their interest in this work. Two of the authors D. K. C. and G. W.. acknowledge the Swedish Board for Space Activities, Stockholm and the third P. C., acknowledges the Swedish Institute, Stockholm for financial support.
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