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Some questions of the night-time ionospheric E region formation in middle latitudes
Planet. SJAIC#Scl., Vol. 24, pp. 139 to 145. Pcrmmmt Press, 1976. Printed in Northern
Ireland
SOME QUESTIONS OF THE NIGHT-TIME IONOSPHERIC E REGION FORMATION IN MIDDLE LATITUDES YU.K.
CHASOVITIN
and V. P. NESTEROV
Hydrometerological Service of the U.S.S.R., Moscow, U.S.S.R.
(Received 4 Juti 1975)
Abstract-An attempt is made to analyse known experimental data on electron density and ion composition of the night-time ionosphere; the main ideas on the night-time E region ionization source are considered; the role of dynamic processes in the irregular structure formation of the night-time ionospheric E region is discussed. The night-time ionospheric E region differs significantly from that of the daytime in its properties as well as in physical processes. Extensive experimental material on the behaviour of the daytime ionosphere obtained by ground and rocket methods allowed one to make some progress towards the construction of the daytime ionospheric model. Data on the nighttime E layer are insuiiicient even for the construction of a preliminary model, however, the experimental material accumulated makes it possible to analyse physical processes of the twilight and night-time ionosphere in middle latitudes. 1. ELECTRON DENSITY VARIATIONS AT lOO-20Okm DURING THE NIGHT-TIME
Diurnal electron density variation in the ionosphere have been analysed by many investigators (e.g. Rawer and Rama Krishnan, 1972; Soboleva, 1973; Belinskaya and Koshelev, 1973; Maeda, 1969, 1971, 1972; Knight, 1972), but in practically all these studies only the general peculiarities of electron density behaviour were considered, and detailed analysis of the n, variation behaviour in the night-time ionosphere at lOO-200km was not carried out. Such analysis was performed by Chasovitin and Nesterov (1975). Fifty-nine experiments were considered in which electron density was measured by direct rocket methods. The list of experiments used is given by Chasovitin and Nesterov (1975). The electron density dependence on the solar zenith angle at fixed heights is shown in Fig. 1. Account was taken of different seasons (winter, summer, equinox) and different solar @ia., < 100, 100 < FIo., -C 150, 150 Q F,., < 20% F,,., > 200)
and geomagnetic (K, < 3 +, K, > 3 +) activities. The symbols used are given in the legends to Fig. 1. Experimental points in Fig. 1 were taken from the corresponding n,(z)-profiles. At the heights where sharp irregularity of the electron density profile (e.g. the E, layer) was noted, the n, value was taken on a background of this irregularity. To establish peculiarities of the electron density behaviour, the results obtained during sunrise and sunset were considered separately. The curves describing the n, variation depending on the solar zenith angle in accordance with the theoretical model of Keneshea et al. (1970) are also given in Fig. 1 for 100-140 km (curves No. 1). It is seen from the figure that during the nighttime, there is considerable scatter in the experimental data at all heights. Reasons for this scatter appear to be: (a) intensity variation of the night-time ionization source; (b) deformation of electron density profiles at the expense of the vertical charged particle drift and in particular the influence of the irregular structure of the n,(z)-profiles typical of the night-time ionosphere; (c) peculiarities of electron density variations in different seasons; (d) the influence of solar and geomagnetic activity. The analysis of experimental data, among which there were only two cases when Kz, > 4, showed that on the basis of the experiments considered it is impossible to find any definite dependence of electron density on the KD index. There is only one point where Kp = 8 (point 1). It is seen from Fig. 1 that electron density registered in this experiment at 100-120 km differ little from the results obtained at 139
Yu. K. -so=
140
and V. P. NEWEROV
Irregularity of the night-time ionization source can make a significant contribution to the scatter in experimental data. From general considerations one can suppose that intensity of this source and its variability should be connected with the solar and geomagnetic activity. However to find this connection it seems to be necessary to use, instead of the solar flux at 2800 MHz&.,) and the I& index, some other more detailed characteristics of solar and geomagnetic activity. To our mind the scatter in the experimental n, values is due to variability of the night-time ionization source and irregular structure of the n,(z)-profiles. To exclude to a certain degree the influence of irregular structure the points considered above were not taken into account while analysing the mean n, I I III I I. 200 km dependence on X. Some other points (e.g. 9-12) were not taken into account either though the reasons for their deviation from the mean n, values remained obscure. In spite of significant scatter in the experimental data one can try to find out de&rite tendencies characterizing the electron density dependence on the solar zenith angle during the night-time. Let us Sunrise sunris-e sunset Sunset Grst consider the n, dependence on x after sunset, X0 the analysis being carried out from 160-200 km FIG. 1. ELECTRON DENSITYDEPENDENCE OF THE SOLAR where the scatter in the experimental data is the ZENITH ANGLE AT FIXED HEIGIi’l3. smallest. To stress the observed dependence at o-l& < 100, O--100< F,,., < 150, A-150< these heights the experimental points were visually Flv, < 200, ~--F,,., > 200; light marks--1IT,g 3+, connected by mean curves (curve No. 3); the points dark marks-_% > 3 + ; i%summer, @-winter. 1: theoreticalmodel ofKenes%aetal(l970); 2: theoretical falling out of general totality were not taken into As is seen from Fig. 1, the electron calculations of Tohmatsu and Wakai (1970); and 3: account. mean curves from experimental points. density during sunset decreases rather quickly, then at x m 100” this decrease slows down and after x w 130’ the electron density decreases again lower KD values, but above 130 km it signilicantly reaching its night-time value at x w 140’. At exceeds the n, values obtained at lower geomagnetic 100-140 km one can also note a similar dependence activity. The n, dependence on the solar radiation though it is masked by a significant scatter in the flux is also not established. The analysis of data showed that most of the points. From comparison between obtained results and points having a considerable scatter in the data theoretical curve No. 1 at 100-140 km it is clear that relative to some mean n, values refer to electron during sunset for the 80-90” zenith angle interval the density profiles characterized by a significant irregular structure. Such points in the figure are experimental points fall within the calculated curves. However at x = lOO-130’ the experimental it, values noted by numbers 2-6. In those cases when irregin a majority of cases exceed the theoretical values ular structure is expressed weakly the experimental (the mean values of electron density in this zenith points do not fall out of the general totality of data. angle interval are noted by lines No. 3). DiscrepanIt should be noted that in some cases the n, values cies between experimental and theoretical curves for obtained in summer (points 2,3,7,8) are lower than those for winter and equinox (in Fig. 1 results of the zenith angles of lOO-130’ seem to be due to the summer and winter experiments are shown by fact that in the theoretical model (Keneshea et al., dashed and solid circles, respectively). This seems 1970) intensity of the night-time ionization source was considered to be constant and its variations with to show that an irregular structure is clearly evident the solar zenith angle were not taken into account. in summer. It is interesting that such a peculiarity As is shown (Meier, 1969; Meier and Manya, 1973) is observed only in the first half of the night. I
I
141
Night-time ionospheric E formation in middle latitudes intensity of scattered ultraviolet radiation varies gradually with the increase of the solar zenith angle; it decreased up to x M lOO-110’ rather slowly and then more quickly (Meier, 1969; Meier and Manya, 1973). This offers the following qualitative explanation of the mean experimental n, dependence on x during the sunset: in the 80-90” zenith angle interval the n, value decreases as a result of variation of the full ionizing flux; at 90” < z < 120” the decay of electron density decreases due to the fact that ionization during some of the time is supported by scattered ultraviolet radiation; at x > 120’ n, rapidly falls to the night-time values corresponding to minimum intensity of the ionization source. Tohmatsu and Wakai (1970) calculated the electron density variation in the E layer maximum during the night with allowance for intensity variations of scattered Ls radiation with the solar zenith angle. The observed dependence is shown in Fig. 1 (curves No. 2,100 and 110 km). It is seen that allowance for the intensity variation of the night-time ionization source will improve the agreement between theoretical and experimental values of electron density in appropriate zenith angle intervals and hence will allow one, as a frrst approximation, to explain the main peculiarities of the observed n, dependence on x after the sunset. At solar zenith angles from 140’ after sunset and to 120-100’ before sunrise the electron density is almost constant and agrees with theoretical values in the order of magnitude (Keneshea et al., 1970). Increase of electron density begins before sunrise at z M 12&100° and proceeds more quickly than the nd decrease after sunset. Such asymmetry of the n, variation during the night was also noted by Starkova (1973). It is defined to a certain degree by the inertial property of ionospheric plasma as a result of which electron density variations lag behind relative to variations of the ion production rates (Ivanov-Kholodny and Nikolsky, 1969). The time of this lag At = (2a’n,)-’ therefore varies during the night according to n, variations and result in a more gradual decrease of electron temperature during sunset and a sharp increase during sunrise. As is seen from Fig. 1, electron density variations during sunrise agree satisfactorily with the theoretical dependencies; the main course of experimental points at 100 and 110 km in the appropriate zenith angle interval being somewhat better described by the curve calculated by Tohmatsu and Wakai (1970). 2. ION COMPOSITION OF THE NIGHT-TIME IONOSPHERE
Data on the concentration
of NO+ and O,+ ions
FIG.
2. DEPENDENCE OF NO+ THE
The
SGLAR
ZENITH
ANGLE.3
ION AT
CONCENTRATIONS FIXED
ON
HEIGHTS.
symbols are the same as for Fig. 1. “M” denotes the cases when [M+] > n.13.
obtained by mass-spectrometer methods for some fixed heights are shown in Figs. 2 and 3. The list of rocket launches used is given by Chasovitin and Nesterov (1975). The symbols are the same as in Fig. 1. The points noted by “M” correspond to the cases where in a given height region quite a number of metallic ions ([Ml > n,/3) are present. At 100-140 km the curves corresponding to the theoretical model of Keneshea et al. (1970) are shown by a solid line. As is seen from Figs. 2 and 3, the body of experimental data is too sparse to establish detiite regularities of [NO+] and [02+] variations depending on X. One can note only the main features characterizing the behaviour of NO+ and O,+ ions during the night. Thus concentration of both ions decreases after sunset, as far as electron density is concerned, a tendency to a more gradual decrease of ni at z = lOO-130° also being observed. In a majority of the cases concentrations approach night-time values at z = 120-140’ and have the mean value of about (l-2) x 109 cmm3 for [NO+] and lOa cmT3 for [Os+], though for [Oaf] much lower values are registered, which in some cases are related to the presence of metallic ions (Narcisi et al., 1967; Philbrick et al.,
YIAILCHASOVITINand V. P. I%XEROY impossible to find out from known experiments any de&rite dependence of ion concentrations on the value of the solar flux at 2800 MNz. It is impossible also to establish the ni dependence on &,, at least for those limits of its variation which have been observed in considered experiments. The experimental data obtains do not allow one to find out any peculiarities connected with different seasons. For C@ ions at x > 80’ the very few massspeetrometric me~~ern~ts makes it impossible to construct the [O+] dependence on x for different heights. All known results of [O-t] mea~em~ts for the X00--20Okm height region are given in Fig. 4 (Chasovitin and Nesterov, 1375). It is to be noted that in the majority of cases O+ ions are registered at night beginning from 16Okm although in some experiments they are found at 100-140 km. As to the 0’ dependence on x one can note that at 200 km the O+ concentration is much lower at the 130-140’ zenith angles than at x = 9%100Q. From the experimental data obtained it is impossible to say ~~hing definite about the [O+] dependence on F,., and 1y,.
IO”
I~N~A~O~ SOURCES THE IONOSPHERK! E REGION
3. ~~~-~ pio.3.
~EP~~CaOFOp+IONCON~~TIO~ON~ SOLAR ZZFSITHANGLE AT FIXED HEIffHTS. for
F&,1. “M”denotesthe cases when [M*l > nd3.
~e~~~~s~~es~e~
1967). An increase of ion concentrations before sunrise is observed at x M lO@, however the few experimental points do not alIow one to follow in detail the ng variation during sumise. For lack of data it is difficult to campare experimental data with theoretical curves shown in Figs. 2 and 3. It should be noted that in general outline the theoretical dependencies properly reflect mean variations of ion concentrations with the solar zenithangle. Cbaracteristic dWerences between experim~tal and th~reti~al data as well as for electron density are observed for the 1~13~’ zenith angles after sunsei. Danilav and Vlasov (1973) supposed that during the night-time at x > lOO-105’ the behaviour of ion components (NO+, O,+> is deflued by location latitude, solar activity and disturbances in the ionosphere and not by the x value and the time elapsed after sunset. The authors cite experimental data which really show significant difference between NO+ and O,+ concentrations in middle and high latitudes. Such a difference seems to be due to the different nature of the night-time ionization source in these latitudes. Nowever if data only for middle latitudes are considered. as is seen from Pies. 2 and 3, it is
OF
At present there are three main viewpoints on the nature of the night-time ionization source. Some
~0’1, FIG.&
M&~smrn~T
cm+
RILWLTS ax+0’ CoNCENTRAnoNs km 'HEIGHT RJZGION.
AT x = 80” IN THB 100-2#
7Jhevalues
of solar zenith angle shown on the curves were used while measurements.
Night-time ionospheric E formation in middle latitudes
x” RCS. 5. TIIB
[NO+]n,/[Or+] DEPENDENCE ON THE SOLAR ZENlIT ANGLE AT 120km. 1: the theoretical model of Keneshea et al. (1970); 2 and 3: minimum values of lliOf]n,/[Of] due to ionization by the electron ffux for different NO eonuntratlons; (3: Barth, 1966; and4: Krasnopolsky, 1970). authors (IvauovXholodny and Niiolsky, 1969; Autouova et aZ., 1972) suppose that the night-time ionization is supported by electron fluxes, others (Fuji&a et al,, 1971; Meier, 1970; Ogawa and Tohmatsu, 1966; Swider, 1972) assume that it is supported by scattered ultraviolet radiation; and yet others suggest that meteor and micrometeorite fluxes provide for the night-time E region ionization. We carefully analysed each ot these sources (Chasovitin and Nesterov, 1975; Nesterov, 1974, 1974a). The ~O+]~~~[O~~J parameter used in some works earlier (Danilov and Vlasov, 1973) was taken as a criterion for de&&ion of the role of scattered U.V. radiation and corpuscular fluxes iu the nighttime E region ionization. This value has no wide scatter during the day. In Fig. 5 experimental values of the ~O+~~~[O~~] parameter for 12Okm are plotted from experimental data. The values, calculated with allowance for the fact that scattered L, and Lb radiation is the ionization source, are also given in Fig. 5 (curve No. 1). From comparison of the experimental [NO+ln,/[O,+l parameter values with the calculated curve one can conclude that up to x = llo’theyare~good~~ment. At x > 120° the calculated @IO-Q&f [OS+]values are constant and equal to 2 x 104cm+ (according to the model of L, and L,, radiation chosen by Keneshea ef al., 1970) while the experimental values continue to decrease. A more detailed model of scattered L, and Ls radiation fluxes (e.g. Meier, 1969; Meier and Manya, 1973) can give better agreement between
143
experimental and theoretical iNO+lns/[Oa+l values. Detailed analysis of the role of a corpuscular ionization source carried out by Chasovitin and Nesterov (1975) and Nesterov (1974a) showed that observed [No+&f[O$] values at x > 100” can be explained by this source. It appeared that for such a source the minimum ~~~~~[O~~] value is determined mainly by reaction constants and neutral component con~ntrations. So for 12Okn-1, using Os, N, and 0 concentrations from the CIBA-1965 model, one can obtain minimum [Nofln,/[Oa~] values equal to 3.1 x Iti and 8.7 x I@ cmea with NO determined by Barth (1966) and Krasnopolsky (1970) respectively (in Fig. 5 these values are shown by horizontal lines No. 2 and 3). Hence the corpuscular hypothesis cau not explain the experimental [NO+]n,/fOZ+] parameter values which are less than those pointed out. Similar calculations and detailed analysis were also carried out for 100 and 110 km and the analogous results were obtained. While analysing the role of meteor fluxes in the upper atmosphere ionization it is established that meteor ionization is not predominant for the ionosphere. The main result of interaction between meteoric matter and the Barth’s atmosphere is the accumulation of metallic atoms and ions in the atmosphere and not ionization. Metallic ions are formed mainly due to ion-molecular reactions of metallic atoms with atmospheric ions. Then they are redistributed into the layers under the action of dynamic processes. Background ionization of the night-time E region resulting in the atmospheric ion formation is spe&f?ed by the action of some other main ionization source. To our mind scattered U.V. radiation can he considered as such a source at least under quiet geomagnetic situations. 4. THE ROLE OF DYNAMIC PROCESSES IN THE FORMATION OF IRREGULAR NIGHTTIME IONOSPHERIC STRUGTURE At present there is a firm belief that the irregular structure of electron density profiles in the midlatitude E region is related to dynamic processes (Nesterov and Chasovitin, 1970; Axford, Cunnold and Gleeson, 1966). III accordance with a wind shear theory the electron density maxima as a 8rs.t approximation must be formed in those nodes of the E-W wind component where it changes its direction from east to west with the height. It follows from more strict considerations that these maxima should be formed in the height region where convergence of the ion velocity field (-VV,) is positive. They include the Ievels where the vertical ion velocity component is equal to 0 with a negative height
144
Yu. K. t%ASOVlTINand
derivative. We considered Hty experimeuts for which conv~~n~e and electron density are known (Chasovitin and Nesterov, 1975). We found that as a given approximation in 88 % of cases the inoreased electron density layers are formed at predicted heights and this accounts for 92% of the total number of registered n, maxima, i.e. most of the maxima are explained by a wind shear theory. So an occurrence of positive convergence regions in most cases is a necessary and s~c~ent-con~tion for formation of the electron density rn~rn~ at a given height. This shows that the i~e~ar structure of electron density profiles typical of the ni~t-tie ionospheric E region is due mainly to dynamic proprocesses which are characteristic of a given atmospheric region and is one of the rn~~~tio~ of ~te~~~tion between charged and neutral atmospheric components. It is clear that the influence of dynamic processes on charged particle ~dis~ibution can best be found while calculating electron density pro&s versus height with allowance for these processes. Appropriate equations were e~ta~ed and solved by Ch~ovit~ and Nesterov (197% Nesterov and Gordeev (1972), Ignatjev et al. (1973), Fujitaka et al. (1971) and Fujitaka (1972). By way of example let us consider calculation of electron density profiles for the experiment carried out on 22 Feb~~ 1968 at 0602 EST on Wallops Island {Smith, 1970; .&dingier, 1969). For this experiment the ~~~z~pro~e was calculated as a q~i-stations
V. I’. Nxsrsaov
approx~ation under the ass~ption that the effective r~omb~ation coeflicient was equal to 2 x lo-’ cm3@(T = 420 K) and the scattered J$ radiation flux was 35 R. The calculation was carried out with no ~10~~~ for the long-lived (metallic) ion redist~bution; the results obtained are given in Fig. 6. It is seen that the theoretical n, profile calculated with allowance for the vertical charged particle drift (curve No. 2) is in satisfactory agreement with experimental results (curve No. l)- At the same time the ~~~~~profilecalculated with no ~lowan~ for the vertical charged particle drift (curve No. 3) ditkrs silently from the experimental proHe. So the results presented in Fig. 6 clearly point to the role of dynamic processes in the fo~ation of the night-TV ionospheric E region. Absence of the electron density rn~~ (calculated curve No. 2) at 93 km which is observed on the experimental profile, and difkence between experimental and calculated n, values in the layer maximum at 109 km, can be expIained by the fact t&it longlived ion r~is~ibution was not taken into accouut. We have calculated twenty fuzz)-profile and in most cases satisfactory agreement with experimental results (Chasovitin and Nesterov, 1975) was observed. All this confirms that the irregular structure of electron density profiles typical of the ~ght-time E region is due to dynamic processes. In conclusion let us consider some problems associated with the ~ght-time ionosph~~ E region which remain to be solved. From some theoretical problems the transition from consid~atio~ of quasi-stations conditions to ~v~t~gation of the formation of increased electron density layers in the process of their dynamic development is of primary importance. If the dynamics of development, wind structure variations and appropriate variations of charged particle prosles are taken into account it is possible to approach real tuitions. Accuracy of th~retical ~~~a~o~ can be silently increased if electrical fields and the vertical wind component are taken into account, but it is still d~c~t because of the absence of reliable experimental data on these parameters. ~~t~~c ions play an impo~~t role in the formation of increased electron density layers. They are effectively redistributed under the action of wiuds. In this connection, of primary importance FIGS. 6. E&P ~~ (1) AND ~~~~A~ EPSON are th~retic~ and e~r~ental ~v~tigatio~s of EXlMilY PROFilES WITH ALLOWANCR (2) AND WITH NO formation, disappearance and transfer processes of ALLOWANCE (3) FOR THE b’BRTICAL CHARUED PARTICLE long-lived ions as well as the problems of construcDrn. Wallops Island, 22 February 1968, O6:02EST (Smith, tion of photochemical models and appropriate theoretical profiles for such ions. 1970; Bedingerand Constantinides,1969).
Night-time ionospheric E formation in middle latitudes
In some cases exper~ental tasks are dictated by r~~erne~ts of the theory. For example, to make theoretical calculations more precise it is necessary to carry out accurate simultaneous electric field and wind measurements. Complex experiments with ~~~1~~~s me~~ements of wind, electron density and temperat~e, neutral gas tem~rat~, ion and neutral composition, electric fields, ionizing radiation, etc. are necessary. Of extreme importance are special experiments with investigation of development dynamics and variations of wind pro&s and electron and ion concentrations. In this connection it is necessary to carry out s~ult~~us measurements of wind and charged particle con~utrations several times a day at short time intervals; this permits calculations which are not confined to a quasi-equilibrium approximation. Such experiments make it possible to specify the character of wind structure variations during the night. Further development of the theory enables the model of the ~~ht-t~e ionospheric E region with allowance for dynamic processes to be constructed. RRPRRBNCES Antonova, L. A., Ivauov-Kholodny, G, S. and Kazatchevskaya, ‘I’.V. (1972). Aeron. Rep&No.48 COSPAR Symp. on D aud E region Ion Chemistry. An information sym~ium record (Eda. C. F. Se&r&, Jr. and M. A. Geiier), p. 127. University of Illinois. Axford, W. I., Cunnold, D. M. aud Gleeson, L. (1966). Plontrt. Space Sci. 4,909. Bedinper, J. F, and Constantinidm, E. (1969). Renort A m&ted at XII session of CGSPAR, Prague. Be mskava. S. I. and Koshelev. V. V. (1973). In:
P
Invest&a&on on Geomqptizm,’ Aeronomi ani Solar Physics 29, p. 121. Moscow, Nat&a. Barth, C. A. (1966). Amt. Geophys. 22,198.
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Chasovitin, Yu. K. and Nesterov, V. P. (1975). ~ynarni~ Processes and the ~i~hf-ti~ ~o~sp~ric E iregion Formatian. Trudy IEM, Gidrometeoizdat, Moscow,
3(55). Danilov A. D. and Vlasov M. N. (1973). P~toche~~try of Ionizedand Ex~~edParf~cies in the Lower Ionosphere.
Gi~met~~dat, Leningrad. Fuiitaka K. (1972). J. atmos. ferr. Phvs. 34. 1615. F&&a 9.; Qgawa T. and To~~~~ T. (1971). J. a#mas. terr. Phys. 33,687.
Ivanov-Kholodny G. S. and NikoIsky G. M. (1969). The San and ~o~osp~re. Moscow, Nauka. Ignatjev, Yu. A., Krotova, 2. I., Neaterov, V. P. and Chasovitirt, Vu,. K. (i973). Radio Phys. 16,11&k Keneshea, T. 3. and Narcisi, R. S. and Swider, W. 3, (1970). J. geap~ys. Res. 75,845. Knight, P. (1972). J. atmos. #err. Pi&w. 34,401, ~~nopol$~y, V. A, (1970). Gary. heron. 10, 837. Maeda. K. (1969). J. Geomapn. Geoelectr. 21.557. Maeda; K. (1971). J. Geoma&. Geoelectr. 23; 133. Maeda, K. (1972). Spece Res. 12,122P. Meier, R. R. (1968). J. geophys. Res. ‘74,356l. Narcisi, R. S., Baily, D. Y. and Della Lucca, L. (1967). Space &s. 7,186. Nesterov. V. P. (1974). Geom. Aeron. 14,445. Nesterovi V. P. (1974a). J. af;os. terr. Pizyi. 36,1753. Neaterov. V. P. and Chasovitin. Yu. K. 11970). Trudv ’ IEM, Gidrometeoizdat, Moscow, 16,26. ’ Nesterov, V. P. and Gordeev, N. B. (1972). Trudy IEM, Gidrometeoizdat, Moscow, 1(34), 21. Ogawa, T. and Tohmatsu, T. (1966). Rep. lonosph. Space Res. Japan 20,395.
Philbrick, C, R. and Narcisi, R. S., Good R. E., Hoffman H. S., Keneshea, ‘I. J., MacLeod, M. A., Zimmerman, S. P. and Reinisch, 3. W. (1373). Space Res. 13,441. Rawer K. and Rama Krishnan, S. (1972). Tentative tables of electron density and excess electron temperature for temperate latitudes. Arbeits gruppe f. Physik. Wehraumfursshung. Freibury F. R. G. August. Smith L. G. (1970). J. atmas. terr. Phys. 32,1247. Soboleva T. N, (1973). Geomagrz.Aeron. 13,932. Starkova A. G. (1973). Geomagn. Aeron. 13,1033. Swider W. (1972). J: atmos, terr. Phys. 34,1615, Tohmatau ‘I’.and Wakai N. (1970). A~~.geop~ys. 26,209.
Ireland
SOME QUESTIONS OF THE NIGHT-TIME IONOSPHERIC E REGION FORMATION IN MIDDLE LATITUDES YU.K.
CHASOVITIN
and V. P. NESTEROV
Hydrometerological Service of the U.S.S.R., Moscow, U.S.S.R.
(Received 4 Juti 1975)
Abstract-An attempt is made to analyse known experimental data on electron density and ion composition of the night-time ionosphere; the main ideas on the night-time E region ionization source are considered; the role of dynamic processes in the irregular structure formation of the night-time ionospheric E region is discussed. The night-time ionospheric E region differs significantly from that of the daytime in its properties as well as in physical processes. Extensive experimental material on the behaviour of the daytime ionosphere obtained by ground and rocket methods allowed one to make some progress towards the construction of the daytime ionospheric model. Data on the nighttime E layer are insuiiicient even for the construction of a preliminary model, however, the experimental material accumulated makes it possible to analyse physical processes of the twilight and night-time ionosphere in middle latitudes. 1. ELECTRON DENSITY VARIATIONS AT lOO-20Okm DURING THE NIGHT-TIME
Diurnal electron density variation in the ionosphere have been analysed by many investigators (e.g. Rawer and Rama Krishnan, 1972; Soboleva, 1973; Belinskaya and Koshelev, 1973; Maeda, 1969, 1971, 1972; Knight, 1972), but in practically all these studies only the general peculiarities of electron density behaviour were considered, and detailed analysis of the n, variation behaviour in the night-time ionosphere at lOO-200km was not carried out. Such analysis was performed by Chasovitin and Nesterov (1975). Fifty-nine experiments were considered in which electron density was measured by direct rocket methods. The list of experiments used is given by Chasovitin and Nesterov (1975). The electron density dependence on the solar zenith angle at fixed heights is shown in Fig. 1. Account was taken of different seasons (winter, summer, equinox) and different solar @ia., < 100, 100 < FIo., -C 150, 150 Q F,., < 20% F,,., > 200)
and geomagnetic (K, < 3 +, K, > 3 +) activities. The symbols used are given in the legends to Fig. 1. Experimental points in Fig. 1 were taken from the corresponding n,(z)-profiles. At the heights where sharp irregularity of the electron density profile (e.g. the E, layer) was noted, the n, value was taken on a background of this irregularity. To establish peculiarities of the electron density behaviour, the results obtained during sunrise and sunset were considered separately. The curves describing the n, variation depending on the solar zenith angle in accordance with the theoretical model of Keneshea et al. (1970) are also given in Fig. 1 for 100-140 km (curves No. 1). It is seen from the figure that during the nighttime, there is considerable scatter in the experimental data at all heights. Reasons for this scatter appear to be: (a) intensity variation of the night-time ionization source; (b) deformation of electron density profiles at the expense of the vertical charged particle drift and in particular the influence of the irregular structure of the n,(z)-profiles typical of the night-time ionosphere; (c) peculiarities of electron density variations in different seasons; (d) the influence of solar and geomagnetic activity. The analysis of experimental data, among which there were only two cases when Kz, > 4, showed that on the basis of the experiments considered it is impossible to find any definite dependence of electron density on the KD index. There is only one point where Kp = 8 (point 1). It is seen from Fig. 1 that electron density registered in this experiment at 100-120 km differ little from the results obtained at 139
Yu. K. -so=
140
and V. P. NEWEROV
Irregularity of the night-time ionization source can make a significant contribution to the scatter in experimental data. From general considerations one can suppose that intensity of this source and its variability should be connected with the solar and geomagnetic activity. However to find this connection it seems to be necessary to use, instead of the solar flux at 2800 MHz&.,) and the I& index, some other more detailed characteristics of solar and geomagnetic activity. To our mind the scatter in the experimental n, values is due to variability of the night-time ionization source and irregular structure of the n,(z)-profiles. To exclude to a certain degree the influence of irregular structure the points considered above were not taken into account while analysing the mean n, I I III I I. 200 km dependence on X. Some other points (e.g. 9-12) were not taken into account either though the reasons for their deviation from the mean n, values remained obscure. In spite of significant scatter in the experimental data one can try to find out de&rite tendencies characterizing the electron density dependence on the solar zenith angle during the night-time. Let us Sunrise sunris-e sunset Sunset Grst consider the n, dependence on x after sunset, X0 the analysis being carried out from 160-200 km FIG. 1. ELECTRON DENSITYDEPENDENCE OF THE SOLAR where the scatter in the experimental data is the ZENITH ANGLE AT FIXED HEIGIi’l3. smallest. To stress the observed dependence at o-l& < 100, O--100< F,,., < 150, A-150< these heights the experimental points were visually Flv, < 200, ~--F,,., > 200; light marks--1IT,g 3+, connected by mean curves (curve No. 3); the points dark marks-_% > 3 + ; i%summer, @-winter. 1: theoreticalmodel ofKenes%aetal(l970); 2: theoretical falling out of general totality were not taken into As is seen from Fig. 1, the electron calculations of Tohmatsu and Wakai (1970); and 3: account. mean curves from experimental points. density during sunset decreases rather quickly, then at x m 100” this decrease slows down and after x w 130’ the electron density decreases again lower KD values, but above 130 km it signilicantly reaching its night-time value at x w 140’. At exceeds the n, values obtained at lower geomagnetic 100-140 km one can also note a similar dependence activity. The n, dependence on the solar radiation though it is masked by a significant scatter in the flux is also not established. The analysis of data showed that most of the points. From comparison between obtained results and points having a considerable scatter in the data theoretical curve No. 1 at 100-140 km it is clear that relative to some mean n, values refer to electron during sunset for the 80-90” zenith angle interval the density profiles characterized by a significant irregular structure. Such points in the figure are experimental points fall within the calculated curves. However at x = lOO-130’ the experimental it, values noted by numbers 2-6. In those cases when irregin a majority of cases exceed the theoretical values ular structure is expressed weakly the experimental (the mean values of electron density in this zenith points do not fall out of the general totality of data. angle interval are noted by lines No. 3). DiscrepanIt should be noted that in some cases the n, values cies between experimental and theoretical curves for obtained in summer (points 2,3,7,8) are lower than those for winter and equinox (in Fig. 1 results of the zenith angles of lOO-130’ seem to be due to the summer and winter experiments are shown by fact that in the theoretical model (Keneshea et al., dashed and solid circles, respectively). This seems 1970) intensity of the night-time ionization source was considered to be constant and its variations with to show that an irregular structure is clearly evident the solar zenith angle were not taken into account. in summer. It is interesting that such a peculiarity As is shown (Meier, 1969; Meier and Manya, 1973) is observed only in the first half of the night. I
I
141
Night-time ionospheric E formation in middle latitudes intensity of scattered ultraviolet radiation varies gradually with the increase of the solar zenith angle; it decreased up to x M lOO-110’ rather slowly and then more quickly (Meier, 1969; Meier and Manya, 1973). This offers the following qualitative explanation of the mean experimental n, dependence on x during the sunset: in the 80-90” zenith angle interval the n, value decreases as a result of variation of the full ionizing flux; at 90” < z < 120” the decay of electron density decreases due to the fact that ionization during some of the time is supported by scattered ultraviolet radiation; at x > 120’ n, rapidly falls to the night-time values corresponding to minimum intensity of the ionization source. Tohmatsu and Wakai (1970) calculated the electron density variation in the E layer maximum during the night with allowance for intensity variations of scattered Ls radiation with the solar zenith angle. The observed dependence is shown in Fig. 1 (curves No. 2,100 and 110 km). It is seen that allowance for the intensity variation of the night-time ionization source will improve the agreement between theoretical and experimental values of electron density in appropriate zenith angle intervals and hence will allow one, as a frrst approximation, to explain the main peculiarities of the observed n, dependence on x after the sunset. At solar zenith angles from 140’ after sunset and to 120-100’ before sunrise the electron density is almost constant and agrees with theoretical values in the order of magnitude (Keneshea et al., 1970). Increase of electron density begins before sunrise at z M 12&100° and proceeds more quickly than the nd decrease after sunset. Such asymmetry of the n, variation during the night was also noted by Starkova (1973). It is defined to a certain degree by the inertial property of ionospheric plasma as a result of which electron density variations lag behind relative to variations of the ion production rates (Ivanov-Kholodny and Nikolsky, 1969). The time of this lag At = (2a’n,)-’ therefore varies during the night according to n, variations and result in a more gradual decrease of electron temperature during sunset and a sharp increase during sunrise. As is seen from Fig. 1, electron density variations during sunrise agree satisfactorily with the theoretical dependencies; the main course of experimental points at 100 and 110 km in the appropriate zenith angle interval being somewhat better described by the curve calculated by Tohmatsu and Wakai (1970). 2. ION COMPOSITION OF THE NIGHT-TIME IONOSPHERE
Data on the concentration
of NO+ and O,+ ions
FIG.
2. DEPENDENCE OF NO+ THE
The
SGLAR
ZENITH
ANGLE.3
ION AT
CONCENTRATIONS FIXED
ON
HEIGHTS.
symbols are the same as for Fig. 1. “M” denotes the cases when [M+] > n.13.
obtained by mass-spectrometer methods for some fixed heights are shown in Figs. 2 and 3. The list of rocket launches used is given by Chasovitin and Nesterov (1975). The symbols are the same as in Fig. 1. The points noted by “M” correspond to the cases where in a given height region quite a number of metallic ions ([Ml > n,/3) are present. At 100-140 km the curves corresponding to the theoretical model of Keneshea et al. (1970) are shown by a solid line. As is seen from Figs. 2 and 3, the body of experimental data is too sparse to establish detiite regularities of [NO+] and [02+] variations depending on X. One can note only the main features characterizing the behaviour of NO+ and O,+ ions during the night. Thus concentration of both ions decreases after sunset, as far as electron density is concerned, a tendency to a more gradual decrease of ni at z = lOO-130° also being observed. In a majority of the cases concentrations approach night-time values at z = 120-140’ and have the mean value of about (l-2) x 109 cmm3 for [NO+] and lOa cmT3 for [Os+], though for [Oaf] much lower values are registered, which in some cases are related to the presence of metallic ions (Narcisi et al., 1967; Philbrick et al.,
YIAILCHASOVITINand V. P. I%XEROY impossible to find out from known experiments any de&rite dependence of ion concentrations on the value of the solar flux at 2800 MNz. It is impossible also to establish the ni dependence on &,, at least for those limits of its variation which have been observed in considered experiments. The experimental data obtains do not allow one to find out any peculiarities connected with different seasons. For C@ ions at x > 80’ the very few massspeetrometric me~~ern~ts makes it impossible to construct the [O+] dependence on x for different heights. All known results of [O-t] mea~em~ts for the X00--20Okm height region are given in Fig. 4 (Chasovitin and Nesterov, 1375). It is to be noted that in the majority of cases O+ ions are registered at night beginning from 16Okm although in some experiments they are found at 100-140 km. As to the 0’ dependence on x one can note that at 200 km the O+ concentration is much lower at the 130-140’ zenith angles than at x = 9%100Q. From the experimental data obtained it is impossible to say ~~hing definite about the [O+] dependence on F,., and 1y,.
IO”
I~N~A~O~ SOURCES THE IONOSPHERK! E REGION
3. ~~~-~ pio.3.
~EP~~CaOFOp+IONCON~~TIO~ON~ SOLAR ZZFSITHANGLE AT FIXED HEIffHTS. for
F&,1. “M”denotesthe cases when [M*l > nd3.
~e~~~~s~~es~e~
1967). An increase of ion concentrations before sunrise is observed at x M lO@, however the few experimental points do not alIow one to follow in detail the ng variation during sumise. For lack of data it is difficult to campare experimental data with theoretical curves shown in Figs. 2 and 3. It should be noted that in general outline the theoretical dependencies properly reflect mean variations of ion concentrations with the solar zenithangle. Cbaracteristic dWerences between experim~tal and th~reti~al data as well as for electron density are observed for the 1~13~’ zenith angles after sunsei. Danilav and Vlasov (1973) supposed that during the night-time at x > lOO-105’ the behaviour of ion components (NO+, O,+> is deflued by location latitude, solar activity and disturbances in the ionosphere and not by the x value and the time elapsed after sunset. The authors cite experimental data which really show significant difference between NO+ and O,+ concentrations in middle and high latitudes. Such a difference seems to be due to the different nature of the night-time ionization source in these latitudes. Nowever if data only for middle latitudes are considered. as is seen from Pies. 2 and 3, it is
OF
At present there are three main viewpoints on the nature of the night-time ionization source. Some
~0’1, FIG.&
M&~smrn~T
cm+
RILWLTS ax+0’ CoNCENTRAnoNs km 'HEIGHT RJZGION.
AT x = 80” IN THB 100-2#
7Jhevalues
of solar zenith angle shown on the curves were used while measurements.
Night-time ionospheric E formation in middle latitudes
x” RCS. 5. TIIB
[NO+]n,/[Or+] DEPENDENCE ON THE SOLAR ZENlIT ANGLE AT 120km. 1: the theoretical model of Keneshea et al. (1970); 2 and 3: minimum values of lliOf]n,/[Of] due to ionization by the electron ffux for different NO eonuntratlons; (3: Barth, 1966; and4: Krasnopolsky, 1970). authors (IvauovXholodny and Niiolsky, 1969; Autouova et aZ., 1972) suppose that the night-time ionization is supported by electron fluxes, others (Fuji&a et al,, 1971; Meier, 1970; Ogawa and Tohmatsu, 1966; Swider, 1972) assume that it is supported by scattered ultraviolet radiation; and yet others suggest that meteor and micrometeorite fluxes provide for the night-time E region ionization. We carefully analysed each ot these sources (Chasovitin and Nesterov, 1975; Nesterov, 1974, 1974a). The ~O+]~~~[O~~J parameter used in some works earlier (Danilov and Vlasov, 1973) was taken as a criterion for de&&ion of the role of scattered U.V. radiation and corpuscular fluxes iu the nighttime E region ionization. This value has no wide scatter during the day. In Fig. 5 experimental values of the ~O+~~~[O~~] parameter for 12Okm are plotted from experimental data. The values, calculated with allowance for the fact that scattered L, and Lb radiation is the ionization source, are also given in Fig. 5 (curve No. 1). From comparison of the experimental [NO+ln,/[O,+l parameter values with the calculated curve one can conclude that up to x = llo’theyare~good~~ment. At x > 120° the calculated @IO-Q&f [OS+]values are constant and equal to 2 x 104cm+ (according to the model of L, and L,, radiation chosen by Keneshea ef al., 1970) while the experimental values continue to decrease. A more detailed model of scattered L, and Ls radiation fluxes (e.g. Meier, 1969; Meier and Manya, 1973) can give better agreement between
143
experimental and theoretical iNO+lns/[Oa+l values. Detailed analysis of the role of a corpuscular ionization source carried out by Chasovitin and Nesterov (1975) and Nesterov (1974a) showed that observed [No+&f[O$] values at x > 100” can be explained by this source. It appeared that for such a source the minimum ~~~~~[O~~] value is determined mainly by reaction constants and neutral component con~ntrations. So for 12Okn-1, using Os, N, and 0 concentrations from the CIBA-1965 model, one can obtain minimum [Nofln,/[Oa~] values equal to 3.1 x Iti and 8.7 x I@ cmea with NO determined by Barth (1966) and Krasnopolsky (1970) respectively (in Fig. 5 these values are shown by horizontal lines No. 2 and 3). Hence the corpuscular hypothesis cau not explain the experimental [NO+]n,/fOZ+] parameter values which are less than those pointed out. Similar calculations and detailed analysis were also carried out for 100 and 110 km and the analogous results were obtained. While analysing the role of meteor fluxes in the upper atmosphere ionization it is established that meteor ionization is not predominant for the ionosphere. The main result of interaction between meteoric matter and the Barth’s atmosphere is the accumulation of metallic atoms and ions in the atmosphere and not ionization. Metallic ions are formed mainly due to ion-molecular reactions of metallic atoms with atmospheric ions. Then they are redistributed into the layers under the action of dynamic processes. Background ionization of the night-time E region resulting in the atmospheric ion formation is spe&f?ed by the action of some other main ionization source. To our mind scattered U.V. radiation can he considered as such a source at least under quiet geomagnetic situations. 4. THE ROLE OF DYNAMIC PROCESSES IN THE FORMATION OF IRREGULAR NIGHTTIME IONOSPHERIC STRUGTURE At present there is a firm belief that the irregular structure of electron density profiles in the midlatitude E region is related to dynamic processes (Nesterov and Chasovitin, 1970; Axford, Cunnold and Gleeson, 1966). III accordance with a wind shear theory the electron density maxima as a 8rs.t approximation must be formed in those nodes of the E-W wind component where it changes its direction from east to west with the height. It follows from more strict considerations that these maxima should be formed in the height region where convergence of the ion velocity field (-VV,) is positive. They include the Ievels where the vertical ion velocity component is equal to 0 with a negative height
144
Yu. K. t%ASOVlTINand
derivative. We considered Hty experimeuts for which conv~~n~e and electron density are known (Chasovitin and Nesterov, 1975). We found that as a given approximation in 88 % of cases the inoreased electron density layers are formed at predicted heights and this accounts for 92% of the total number of registered n, maxima, i.e. most of the maxima are explained by a wind shear theory. So an occurrence of positive convergence regions in most cases is a necessary and s~c~ent-con~tion for formation of the electron density rn~rn~ at a given height. This shows that the i~e~ar structure of electron density profiles typical of the ni~t-tie ionospheric E region is due mainly to dynamic proprocesses which are characteristic of a given atmospheric region and is one of the rn~~~tio~ of ~te~~~tion between charged and neutral atmospheric components. It is clear that the influence of dynamic processes on charged particle ~dis~ibution can best be found while calculating electron density pro&s versus height with allowance for these processes. Appropriate equations were e~ta~ed and solved by Ch~ovit~ and Nesterov (197% Nesterov and Gordeev (1972), Ignatjev et al. (1973), Fujitaka et al. (1971) and Fujitaka (1972). By way of example let us consider calculation of electron density profiles for the experiment carried out on 22 Feb~~ 1968 at 0602 EST on Wallops Island {Smith, 1970; .&dingier, 1969). For this experiment the ~~~z~pro~e was calculated as a q~i-stations
V. I’. Nxsrsaov
approx~ation under the ass~ption that the effective r~omb~ation coeflicient was equal to 2 x lo-’ cm3@(T = 420 K) and the scattered J$ radiation flux was 35 R. The calculation was carried out with no ~10~~~ for the long-lived (metallic) ion redist~bution; the results obtained are given in Fig. 6. It is seen that the theoretical n, profile calculated with allowance for the vertical charged particle drift (curve No. 2) is in satisfactory agreement with experimental results (curve No. l)- At the same time the ~~~~~profilecalculated with no ~lowan~ for the vertical charged particle drift (curve No. 3) ditkrs silently from the experimental proHe. So the results presented in Fig. 6 clearly point to the role of dynamic processes in the fo~ation of the night-TV ionospheric E region. Absence of the electron density rn~~ (calculated curve No. 2) at 93 km which is observed on the experimental profile, and difkence between experimental and calculated n, values in the layer maximum at 109 km, can be expIained by the fact t&it longlived ion r~is~ibution was not taken into accouut. We have calculated twenty fuzz)-profile and in most cases satisfactory agreement with experimental results (Chasovitin and Nesterov, 1975) was observed. All this confirms that the irregular structure of electron density profiles typical of the ~ght-time E region is due to dynamic processes. In conclusion let us consider some problems associated with the ~ght-time ionosph~~ E region which remain to be solved. From some theoretical problems the transition from consid~atio~ of quasi-stations conditions to ~v~t~gation of the formation of increased electron density layers in the process of their dynamic development is of primary importance. If the dynamics of development, wind structure variations and appropriate variations of charged particle prosles are taken into account it is possible to approach real tuitions. Accuracy of th~retical ~~~a~o~ can be silently increased if electrical fields and the vertical wind component are taken into account, but it is still d~c~t because of the absence of reliable experimental data on these parameters. ~~t~~c ions play an impo~~t role in the formation of increased electron density layers. They are effectively redistributed under the action of wiuds. In this connection, of primary importance FIGS. 6. E&P ~~ (1) AND ~~~~A~ EPSON are th~retic~ and e~r~ental ~v~tigatio~s of EXlMilY PROFilES WITH ALLOWANCR (2) AND WITH NO formation, disappearance and transfer processes of ALLOWANCE (3) FOR THE b’BRTICAL CHARUED PARTICLE long-lived ions as well as the problems of construcDrn. Wallops Island, 22 February 1968, O6:02EST (Smith, tion of photochemical models and appropriate theoretical profiles for such ions. 1970; Bedingerand Constantinides,1969).
Night-time ionospheric E formation in middle latitudes
In some cases exper~ental tasks are dictated by r~~erne~ts of the theory. For example, to make theoretical calculations more precise it is necessary to carry out accurate simultaneous electric field and wind measurements. Complex experiments with ~~~1~~~s me~~ements of wind, electron density and temperat~e, neutral gas tem~rat~, ion and neutral composition, electric fields, ionizing radiation, etc. are necessary. Of extreme importance are special experiments with investigation of development dynamics and variations of wind pro&s and electron and ion concentrations. In this connection it is necessary to carry out s~ult~~us measurements of wind and charged particle con~utrations several times a day at short time intervals; this permits calculations which are not confined to a quasi-equilibrium approximation. Such experiments make it possible to specify the character of wind structure variations during the night. Further development of the theory enables the model of the ~~ht-t~e ionospheric E region with allowance for dynamic processes to be constructed. RRPRRBNCES Antonova, L. A., Ivauov-Kholodny, G, S. and Kazatchevskaya, ‘I’.V. (1972). Aeron. Rep&No.48 COSPAR Symp. on D aud E region Ion Chemistry. An information sym~ium record (Eda. C. F. Se&r&, Jr. and M. A. Geiier), p. 127. University of Illinois. Axford, W. I., Cunnold, D. M. aud Gleeson, L. (1966). Plontrt. Space Sci. 4,909. Bedinper, J. F, and Constantinidm, E. (1969). Renort A m&ted at XII session of CGSPAR, Prague. Be mskava. S. I. and Koshelev. V. V. (1973). In:
P
Invest&a&on on Geomqptizm,’ Aeronomi ani Solar Physics 29, p. 121. Moscow, Nat&a. Barth, C. A. (1966). Amt. Geophys. 22,198.
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Ivanov-Kholodny G. S. and NikoIsky G. M. (1969). The San and ~o~osp~re. Moscow, Nauka. Ignatjev, Yu. A., Krotova, 2. I., Neaterov, V. P. and Chasovitirt, Vu,. K. (i973). Radio Phys. 16,11&k Keneshea, T. 3. and Narcisi, R. S. and Swider, W. 3, (1970). J. geap~ys. Res. 75,845. Knight, P. (1972). J. atmos. #err. Pi&w. 34,401, ~~nopol$~y, V. A, (1970). Gary. heron. 10, 837. Maeda. K. (1969). J. Geomapn. Geoelectr. 21.557. Maeda; K. (1971). J. Geoma&. Geoelectr. 23; 133. Maeda, K. (1972). Spece Res. 12,122P. Meier, R. R. (1968). J. geophys. Res. ‘74,356l. Narcisi, R. S., Baily, D. Y. and Della Lucca, L. (1967). Space &s. 7,186. Nesterov. V. P. (1974). Geom. Aeron. 14,445. Nesterovi V. P. (1974a). J. af;os. terr. Pizyi. 36,1753. Neaterov. V. P. and Chasovitin. Yu. K. 11970). Trudv ’ IEM, Gidrometeoizdat, Moscow, 16,26. ’ Nesterov, V. P. and Gordeev, N. B. (1972). Trudy IEM, Gidrometeoizdat, Moscow, 1(34), 21. Ogawa, T. and Tohmatsu, T. (1966). Rep. lonosph. Space Res. Japan 20,395.
Philbrick, C, R. and Narcisi, R. S., Good R. E., Hoffman H. S., Keneshea, ‘I. J., MacLeod, M. A., Zimmerman, S. P. and Reinisch, 3. W. (1373). Space Res. 13,441. Rawer K. and Rama Krishnan, S. (1972). Tentative tables of electron density and excess electron temperature for temperate latitudes. Arbeits gruppe f. Physik. Wehraumfursshung. Freibury F. R. G. August. Smith L. G. (1970). J. atmas. terr. Phys. 32,1247. Soboleva T. N, (1973). Geomagrz.Aeron. 13,932. Starkova A. G. (1973). Geomagn. Aeron. 13,1033. Swider W. (1972). J: atmos, terr. Phys. 34,1615, Tohmatau ‘I’.and Wakai N. (1970). A~~.geop~ys. 26,209.