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Rocket electron density profiles over Volgograd, Heiss Island and Esrange during the DYANA campaign
Jownul o~A~mospkefic und Terresrd
Pergamon
Pkysics, Vol. 56. Nos 13114, pp. 1923-1931, 1994 Copyright 0 194 Elsevier Science Ltd
Printed IIIGreatBritain. All rightsreserved 002l-9169,‘94
0021-9169(94)EOO39-P
$7.00+0.00
Rocket electron density profiles over Volgograd, Heiss Island and Esrange during the DYANA campaign A. K. KNYAZEV*, Z. Ts. RAPOPORT,~ V. M. SINELNIKOV?and M.
FRIEDRICH$
Aerological Observatory, Dolgoprudny, Moscow, Russia; t Academy of Sciences, Moscow, Russia ; $Department of Communications and Wave Propagation, Technical University, Graz, Austria
*Central
(Received in final firm 22 Februq
1994 ; accepted 22 Februar.y 1994)
Abstract-The results of the determination of electron density (N,) profiles at Volgograd, Heiss Island and Esrange ranges are discussed. Some of thqse profiles were obtained at solar zenith angles x90”, but at times near the sunset, and others at night-time. The profiles obtained during the DYANA campaign were compared with others obtained in the past, with solar and geomagnetic indices as well as with the temperature and atmospheric circulation in the stratosphere and mesosphere. The daytime electron densities below 85 km over Volgograd do not show any appreciable connection to the temperature. An anomalous period of low electron densities observed from February to the beginning of March rather seems to be connected with the meridional and vertical components of the atmospheric wind. We can speculate that the high night-time &values at middle latitude may be considered as a manifestation of a post-storm effect. The relationship of the N,-values at higher altitudes (> 80 km) and radio wave absorption seems to be connected with the atmospheric circulation and geomagnetic activity. The I$-values in the polar cap region (Heiss Island) are below those at the same altitude in the aurora1 zone (Esrange), but higher than at middle latitudes (Volgograd). The hi,-values over Heiss island seem to be connected with the geomagnetic activity and the meridional component of atmospheric circulation ; the thermal control of the D-region cannot be excluded.
1. INTRODUCTION
but most of them were launched near sunset; four rockets were launched at x > 90”. All profiles obtained at x < 90” were reduced to x = 88” to compare the absolute values of N,. The normalization is carried out using the expressions given by BELIKOVICH et al. (1983),
Twenty-nine rockets were launched at the different ranges for determination of the electron density N, of the lower ionosphere during the DYANA campaign. The NC-values were determined by different techniques. The data obtained were compared with the data characterizing the geophysical situation during the experiments. N(~) profifes obtained from rocket launchings at other times are shown for comparison. The measured data and their interpretation are presented below for each of the respective rocket launch sites, together with the technique employed.
2. 2. I.
EXPERIMENTAL DATA AND THEIR
N,(h) = N,(h) (COSx)~‘~’
k(h) = Aces ~36O”j, where N, (h) is the electron density profile, obtained at the solar zenith angle (observed and recalculated), N,,(h) is the electron density profile at x = O”, with the following constants :
ANALYSIS
E~ectrost~t~~probe technique
A = 0.9,
2.1.1. vo/olgograd range (48” 41’ N, 44” 21‘ E). Fourteen rockets of the type MlOOB were launched from the Volgograd range during the experimental phase of the DYANA campaign to determine the N,-profiles ; in addition, twp rockets were launched on 3 and 10 January and two rockets were launched on 21 and 28 March 1990. The dates of the launchings, the times and the solar zenith angles (x) are listed in Table 1. We can see that 14 rockets were launched at x < 90”,
B = 80.0 km,
C = 131.9 km.
Figure 1 shows the electron densities between 50 and 85 km in the time period from 5 January to 25 March 1990, no~alized to x = 88” on the basis of 14 rocket launchings. The numbers on the curves denote the electron densities (cms3), and the small arrows on the abscissa indicate the rocket launchings. We note the considerable variability of the N,-values from day to day. A reduction of the N,-values at altitudes above
1923
1924
A. K.
KNYAZEV et al.
so 14, ,lk 5 1015202530 Jan
ibb4
I41 ICI
5 101520251
5 10152025
Feb 1990
Mar
Fig. 1. Altitude-time development of the electron density over Volgograd. The N.-values are normalized to a constant solar zenith angle, x, of 88”. The numbers on the curves denote the electron density values (cm-‘). Arrows indicate the dates of rocket launchings (electrostatic probe technique).
75 km takes place during the second IO-day period in January; at the same time the electron density increases below 75 km. We can see a general tendency of decreasing NC-values after 20 January, but there are periods when NC increases at some altitudes at the same time. These periods are from 22 to 31 January at 80-85 km, from 22 to 25 January at 768 1 km, and from 29 to 31 January at 66-77 km. Low N,-values have persisted all through the second half of February. The NC-values at all altitudes increase after 5 March 1990. It is interesting to compare the variations of the N,values with geomagnetic and solar activity as well as with the temperature and atmospheric dynamics at stratospheric and mesospheric altitudes. Figure 2 shows the geomagnetic activity index A, and the solar activity index F,“,,. It is difficult to find any relationship between A, and F10,7,on the one hand, and the NC-values, on the other. This again confirms the wellknown fact that geomagnetic and solar activity indices correlate poorly at middle latitudes in winter when the correlation is made on a day-to-day basis. We suppose that the increase of the N,-value in March in the altitude region 55-83 km was an effect of considerable solar and geomagnetic activity. A proton event took place on 19 March (it began at 07.05 UT, with a maximum of 140 particles cm-* SK’ sr-’ of
Ionospheric electron density profiles
1925
IO 60 50 40 z 30 20 10 0
5
10 15 20 Jan
25 30 5
10 15 20 25 1 5
Feb 1990
10 15 20 25 30
Mar
Fig. 2. The indices of geomagnetic activity A, and solar activity F,, , from January to March 1990.
greater than 10 MeV at 08.00 UT) ; two geomagnetic storms occurred on 12 and 20 March. The A,-index was more than 70 on 21 March (SOLAR-GEOPHYSICAL DATA, 1990). In contrast, a similar period of enhanced geomagnetic activity in the second half of February coincided with a period of very low NC-values at the altitudes under consideration. The consideration of the altitude-time cross-section at 2&80 km from January to March 1990 (KOKIN et al., 1994) shows that three marked warmings took place in the upper stratosphere : in the middle of January, in February and in March (peak temperatures were observed on 20-25 March). At the same time in January and March the temperature increased in the mesosphere (7080) km) ; from 10-20 February, during the warming in the upper stratosphere, a cooling took place in the mesosphere. This supports the conclusion by ENTZIAN et al. (1971) that the mesospheric temperature varies in antiphase with that of the stratosphere. A comparison of Fig. 1 with the altitude-time temperature cross-section (KOKIN et al., 1994) confirms the conclusion drawn by OFFERMANNet al. (1979) that temperature is not the main factor which determines the variations of electron density in the mid-latitudinal lower ionosphere. The altitude-time pictures of variations of the zonal and meridional components of the wind velocity in the stratosphere and mesosphere over Volgograd are shown by KOKIN et al. (1994). We can see that the westerly wind dominates at all the altitudes considered. It reached 100 m s-’ between 40 and
60 km during the DYANA campaign ; the mesospheric wind velocities are from 10 to 80 m s-‘. There is large day-to-day variability of the wind. The mesospheric zonal velocity reached its maximum at the end of February and early March. The zonal wind velocity decreased to zero and reversed in the last lo-day period of January and at the beginning of February. At the same time, the NC-values decreased. The mesospheric westerly wind velocity increased at the end of February and at the beginning of March. This enhancement of the wind velocity coincides with the enhancement of the wind velocity at higher altitudes (NAUJOKAT et al., 1990), but a corresponding enhancement of the electron density at altitudes of 70& 80 km cannot be seen. The velocity of the meridional component shows great variability ; for example, at altitudes from 75 to 80 km it varies from -45 to + 35 m SC’. It should be noted that the long period of decreasing electron density, at altitudes 60-85 km, during February to the beginning of March (rocket launchings from 14 February to 5 March) is anomalous : the N,values at these altitudes are the lowest amongst those observed during the corresponding geophysical conditions in 1981-1989. This decrease seems to be connected with the vertical component of the wind velocity, v. The v-values were calculated by the method proposed by IVANOVA et al. (1990) ; it is based on rocket data of the temperature and horizontal wind variations. During this period the direction of v in the mesosphere was always upwards. This decrease of N,-
1926
A. K.
KNYAZEV et al.
012345678910 t
WY)
I
I
102
103
N
1
(e ~rn-~)
Fig. 3. NC-profiles obtained at night over Volgograd on 3 January (profile l), 15 January (2), 17 January (3), 28 March 1990 (4) and the mean night-time profile calculated from the data obtained under quiet geomagnetic conditions in January-December 1981-1989 by the same technique (x = loo”, F,07 i 150, profile 5). In the upper part of the inset is presented the manifestation of the post-storm effect in the night-time winter electron density ; the dots represent the data of 1981-1989, the circles refer to the launch of 3 January 1990. The lower part of the inset presents the average variation of the A,-index during geomagnetic disturbances.
values seems to be connected also with the meridional component of the wind velocity, which was southerly during the period under consideration (KOKIN et al., 1994). Figure 3 shows four N(h)-profiles, obtained at x > 90”, as well as a mean profile calculated from the results of 28 rocket launchings, which were carried out in January and February of 1981-1989 under quiet geomagnetic conditions. The horizontal bars show the 99% confidence intervals calculated on basis of 13-28 N,-values. Profiles 2 and 3 differ from the mean profile very little, but profiles 1 and 4 depart from them considerably. It is possible that the difference of the fourth profile from the mean is connected with the solar zenith angle (x = 91”)-night-time conditions may not yet have fully set in at the altitudes under consideration. Besides, the geophysical conditions preceding this rocket launching were very disturbed. The post-storm event, following the geomagnetic storm which began 5 days prior to the rocket launch of 3 January (SOLAR-GEOPHYSICAL DATA, 1990), might well be the cause of the enhancement of the
night-time electron density at that time. The significance of the post-storm effect for the winter nighttime ionization was shown earlier on the basis of the limited MAP/WINE data set (PAKHOMOVet al., 1986). We consider this effect using the more extensive data obtained from that time and examine how the data of 3 January fit into the whole picture. The analysis technique is described below. We considered the time sequence of N,-values at 80 km and the geomagnetic situation (A,-index) of the preceding 10 days. If during this period there was a day with A, > 24, this day was marked as a key day (zeroday) and the day when the N,-value was determined marked by corresponding figures from 0 to 9. Afterwards all the A, and N, data were combined into one figure. Thus, some modification of the superposed epoch technique was used. The results of the analysis are shown in the inset of Fig. 3; A,-values decrease smoothly from the key day. At the same time the N,values (log N,) decrease to the second day, increase to the fifth day and decrease afterwards. The result of the launch of 3 January agrees fairly well with the dependence obtained on the basis of the whole data determined by the electrostatic probe during nighttime conditions in winter seasons from 1981 to 1989. This effect is analogous to the effects observed earlier in radio wave absorption (LAUTER et al., 1977; N~STOROV, 1986) or in data obtained by the partial reflection technique (SINGER et al., 1987), but the cited data were obtained during the whole daytime, and at twilight. 2.1.2. Heiss Island range (80” 37’ N, 58’ 03’ E). Eleven NC-profiles were obtained during the period from 10 January to 14 March 1990 by MlOOB rockets launched from the Heiss Island range. Table 2 presents the dates and the times of the rocket launches as well as the solar zenith angles. Figure 4 presents the altitude-time section of N,values over Heiss Island during the DYANA campaign. All profiles were obtained for polar night conditions (x > 90”). It is evident that the N,-value variability at Heiss Island is less than at Volgograd. Comparison with solar activity (Fig. 2) does not reveal any correlation of F,,, with N,. At first sight there is also no positive correlation between N, and A,. However, calculations show that the correlation coefficient r(N,, AJ is positive ( >O.S) over the whole altitude range (Fig. 5). This result indicates the role of the incoming fluxes of energetic charged particles for electron density production in the polar cap. Comparison of the N,-values with the altitude-time variabilities of the velocities of the zonal and meridional winds (KOKIN et al., 1994) does not show any clear correlation between N,-values and the values and
1927
Ionospheric electron density profiles Table 2. List of rocket launches from Heiss Island during the DYANA campaign Date 1990
IO Jan.
17 Jan.
31 Jan.
Time UT x
16.22 117”
1505 112”
15.05 109”
5 Feb. 15.05 99”
7 Feb. 19.05 114”
12
21
28
7
12
14
Feb. 15.05 105”
Feb. 16.10 104”
Feb. 15.05 99”
March 15.05 97”
March 15.05 95’
March 15.05 94’
6&I 5
f 11 1 1 1 10 15 20 25 30
ff 5
Jan
A 1 I+ 1 +I 10 15 20 25 1 Feb 1990
If 5
IN 1 t 10 15 20 25 Mar
1 30
Fig. 4. The altitude-time variation of nocturnal NC-values over Heiss Island. The designations are the same as in Fig. 1.
directions of these wind components, but the correlation coefficient between the deviations of the N,values from the regression line N,(A,) and the meridional component of the wind velocity at 80 km is 0.6. This result can be considered as evidence for the significance of the southerly meridional wind in the electron production over Heiss Island. The altitude-time development of the temperature over Heiss Island during the DYANA campaign is presented by KOKIN et al. (1994). Unfortunately, the temperature data were generally obtained below 75 km whereas the N,-profiles begin above that height. It is therefore difficult to draw any conclusion about the influence of the mesospheric temperature on the electron density. Nevertheless, it is possible to note some influence of the temperature regime on the electron density distribution. Indeed, the stratospheric warming in the second half of January was accompanied by a noticeable cooling in the mesosphere, near 70 km. From 15 to 17 January the temperature decreased from - 74 to - 113°C attaining
the lowest values of the temperature observed during the winter period under consideration ; at the same time the N,-values decreased. Some increase of N,values was accompanied by the temperature increase in the mesosphere at the end of January. The most noticeable warming in the higher stratosphere (4060 km) was observed on 7 February; the temperature reached +44”C. At the same time the temperature decreased in the region above 65 km. The lowest N,values during the whole DYANA period were observed on 7 February. There is a tendency for a simultaneous variation of the N, and temperature values at mesospheric altitudes afterwards. At the same time two minor warmings in the higher stratosphere on 19 February and during the period from 7 to 12 March did not accompany the toolings in the mesosphere. Correlation coefficients between &values at 80 km and the mesospheric temperature at 74 km and the stratopause temperature are f0.41 and -0.66, respectively. The absolute values of the correlation
A. K. KNYAZEVet al.
1928
0-0 r (N A& Fig. 5. Correlation coefficient between the N,-values (Heiss Island) and the geomagnetic activity index A, vs. altitude.
coefficients are not large, so they can be considered as evidence for some tendency for the same relationship of electron density with temperature. At the same time this result is in agreement with the results obtained at Heiss Island during the MAP/WINE campaign (PAKHOMOV et al., 1986), when the correlation coefficients of N,-values at the mesopause region with the mesospheric temperature were +0.76. It is difficult to evaluate the significance of each mechanism (temperature and meridional wind) in the electron density production over Heiss Island during the DYANA campaign because both mechanisms acted simultaneously. Besides, this influence is not excluded during the DYANA campaign. This difference seems to explain the clearer relationship between electron density and temperature during the MAP/WINE campaign. It will be recalled that the relationship between electron density and temperature at middle latitudes was not apparent in either case. This difference seems to be connected with the larger variations of the temperature over Heiss Island. Comparison of the night-time N(h)-profiles over Volgograd (Fig. 3) with the profiles obtained at Heiss Island (Fig. 4) shows that in most cases the N,values at Heiss Island at the corresponding altitudes are higher than over Volgograd, which is naturally
N (e cm*)
Fig. 6. The N(h)-profiles obtained at night-time in Volgograd (coherent frequency technique). Profile 1 for 28 February, 2 for 5 March, 3 for 10 March, and 4 for 14 March 1990.
explained by the additional the high latitudes.
ionization
occurring
in
2.2. Coherent frequency technique : Volgograd range Four electron density profiles were obtained by this technique at the end of the DYANA campaign at night (x > 118”). Figure 6 presents these profiles. It is seen that NC-values at 8695 km on 28 February are higher than N,-values at this altitude for the other rocket launchings. For comparison of the N,(h)-profiles with radio wave absorption we used the values of absorption measured in Volgograd at 2.2 MHz (L2 J and the f-min parameter of vertical sounding ionograms. We took the mean value of the medians of fmin parameters obtained in 15 min during the period centred at the moment t (cos x = 0.2) p.m. and at t (cos x = 0.2) a.m., and the mean value of L,, (cos x = 0.2) p.m. and L,, (cos x = 0.2) a.m. as representatives values for the night between the days when these values offmin and L,,, were obtained. The from ionosondes mean _L values were determined near Archangelsk (64” 36’ N, 40” 30’ E), Moscow (55” 28’ N, 37” 19’ E) and Kaliningrad (54” 42’ N, 20” 36’ E). As an index of geomagnetic activity the daily sum of K-index for Moscow @Km) was taken. Values of
1929
Ionospheric electron density profiles Table 3. Geophysical parameters at three sites in Russia during the DYANA campaign Period 1990 2428 Feb. I- 5 March 8-12 March 10-14 March 28 Feb.-l March 5- 6 March 12-13 March 14-t 5 March
$) 47 39 26 27 41 33 24 29
Archangelsk
F,,, (MHz) Moscow
3.0 2.45 1.85 1.6 2.8 2.35 1.75 1.7
2.35 1.9 1.55 1.55 2.35 1.7 1.4 1.7
L,,,, fmln and ZKm thus determined were averaged for five days (nights) preceding the dates of the rocket launchings. These data as well as the data for the days (nights) of rocket launchings are presented in Table 3. The 5-day period before the launching on 28 February was more disturbed than the others. The same situation also prevailed for the nights when the rockets were launched. The geomagnetic activity changed in the same way as the radio wave absorption during this period. The atmospheric circulation in the mesosphere and lower thermosphere during the DYANA period has been described in detail by NAUJOKAT el al. (1990). As the measurements, especially those obtained by the Dl method, show, the launch on 28 February coincides with a period when these are strong westerly winds ; afterwards the wind ceases abruptly, and at 95 km even changes sign. Thus, the geomagnetic activity and atmospheric circulation variations are in accordance with the variations of the radio wave absorption (& fmin) and of the electron density in the upper part of N,-profiles obtained (WILLIAMS et al., 1987). We assume that the profile on 28 February was obtained in a period when winter anomalous conditions occurred in the lower ionosphere (especially at 85 km), and the profiles obtained in March corresponded with the final stratospheric warming, that is to the transition period from the winter anomalous conditions to the normal spring conditions. Figure 7a presents the profiles obtained on 28 February 1990 (profile 1) and on 20 January 1982 (profile 2). The last profile was obtained in Volgograd by the coherent frequency technique at night; profile 2 is similar to profile 1 in shape, but is somewhat lower. The NC-profile 2 is typical for the winter night when winter anomaly conditions prevail. Figure 7b presents the N,(h)-profiles obtained on 5 March 1990 (profile 3) and on 23 May 1979 (profile 4). Profile 4 was
Kaliningrad
CKm
2.35 1.7
31.2 23.8 21.8 26.0 30 23.5 30 23
1.6 1.6 2.0 1.6 1.5 1.6
obtained in summer-time when winter anomaly conditions are absent. Profiles 3 and 4 are very similar in shape, but the maximum N,-value for profile 3 is located 7 km higher than the maximum for profile 4. It should be noted that all four profiles presented in Fig. 7 were obtained during periods of high solar activity. It is difficult to compare the N,(h)-profiles obtained by the coherent frequency technique and by the electrostatic probe technique as they give electron density distributions in different altitude ranges. 2.3. Faraday rotation technique: Esrange (67” 53’ N, 21” 04’ E) One N&)-profile for the altitude range from 68 to 100 km was obtained by this technique. Figure 8 presents this profile (profile 1). The N,(h)-profiles obtained on 26 July 1990 (profile 2) and on 9 April 1991 (profile 3) are also shown in this figure. All the profiles were obtained at x > 90” ; profiles 2 and 3 were obtained at higher solar activity than profile 1. The NC-values of profile 1 exceed those of profiles 2 and 3. There is no basis to ascribe this difference to both solar and geomagnetic activity. We can suppose that this distinction is connected with the known ionospheric variability at high latitudes, and also that it is connected with the winter anomalous conditions which take place at Esrange’s latitude in March ; they are weaker in April and certainly absent in July. Esrange is situated very near the aurora1 zone. This seems to be the main cause of the enhanced electron density values compared with the N,-values obtained at the middle latitude range Volgograd and at the polar cap range Heiss Island. 3. CONCLUSIONS
Electron density profiles in the lower ionosphere obtained with rockets by electrostatic probe, coherent
A. K. KNYAZEVet al.
1930
120 -
120 -
80 -
80 -
102
2
3
57103
23
57
lo2
2
3
N (e em-3)
57103
23
57
N (e cm-3)
Fig. 7. N,-profiles obtained at night over Volgograd by the coherent frequency technique. Fig. 7a. l-28 February
1990; 2-20 January
1982. Fig. 7b. 3-5 March
80
601 10’
I 102
I 103
I 104
I 105
N (e cm-s) Fig. 8. IV,-profiles obtained at night Faraday rotation technique. Profile x = 95”; R = 104; A, = 21. Profile x = 92”; R = 186; A, = 26. Profile ~=95”;R= 188,A,=
over Esrange by the 1 for 6 March 1990; 2 for 26 July 1990; 3 for 9 April 1991; 10.
frequency and Faraday rotation techniques at Esrange, Heiss Island and Volgograd ranges are presented. The N,(h)-profiles at Volgograd were generally obtained before sunset (x = 88”), while others were obtained at night (x > 900). Comparison of the pro-
1990.4-23
May 1979.
files obtained by the electrostatic probe technique at Volgograd with the temperature in the upper stratosphere and in the mesosphere does not reveal any clear relationships. A period of anomalously low electron density, determined by the electrostatic probe technique, was observed in February, up to the beginning of March 1990. This decrease of the electron density seems to be connected with the directions of the vertical and meridional winds which were, at that time, upwards and from the south, respectively. The NC-value variability at night at middle latitudes after magnetic storms is comparatively large and approximately corresponds with the general winter variability. However, variations of the same order can sometimes be observed during periods without preceding geomagnetic storms. The geomagnetic control of such a kind seems to be only one of the winter variability factors. The rocket data on temperature and the dynamical regime of the stratosphere and mesosphere suggest that the lower ionosphere over Heiss Island during the DYANA campaign was not only under the control of geophysical factors, but also under the control of meteorological processes of the middle atmosphere. The N,-profiles obtained at Volgograd during the final stage of the DYANA campaign by the coherent frequency technique at higher altitudes than obtained by the electrostatic probe technique show that the N,-values, at 85-95 km, may be connected both with
Ionospheric electron density profiles winter anomalous conditions and with the atmospheric circulation as well with geomagnetic activity. The N,(h)-profile obtained by the Faraday rotation technique at Esrange on 6 March may be interpreted as being obtained under winter anomalous conditions : the NC-values in the D-region were found to
1931
be larger than the N,-values determined in April and July. At the same time, the NC-values determined for night conditions at Esrange, situated in the aurora1 zone, are higher than the NC-values obtained both at middle latitudes (Volgograd) and in the polar cap (Heiss Island).
REFERENCES BEL~KOVICH V. V., BENEDIKTOV E. E., VYAKHIREVV. D. and GRISHKEVICH L. V.
1983
BUGAEVAI. V., BOUTKOA. I., KOKING. A., KOSHELKOV Yu. P., PEROVS. P., TARASENKO D. A., ZAKHAROVG. R., TOULINOVG. F., OFFERMANN D., BITTNERM., VONZAHN U., CHANINM. L., HAUCHECORNE A., SOULEI., SUBBARAYA B. H., GIL-OJEDAM., DELA MORENA B. A., SCHMIDLIN F. J., OYAMAK. I. and KANZAWA H. ENTZIANG., GAIGEROVS. S. and TARASENKO D. A.
1994
IVANOVAI. N., KOKING. A., LYSENKOE. V., PEROVS. P., ROSENFELD S. C. and CHIZHOVA. F. LAUTERE. A., BREMERJ., DETERSI. and EVERSK. NAUJOKATB., LABITZKEK., LENSCHOV R., PETZOLDK. and WOHLFARTR.-C.
1971 1991 1977
Catalogue of the electron density profiles of the middle latitude ionospheric D-region. Preprint of NIRFI N 171, Gorky, 51 p. (in Russian). J. atmos. terr. Phys., 56, 1659.
Transactions of the Academy of Sciences of the U.S.S.R. Phys. armos. Oceans 7,932 (in Russian). Met. Hydrol. 5, 39 (in Russian).
NESTOROV G.
1986
OFFERMANN D., CURTISP., CISNEROS J. M., SATRUSTECUI J., LAUCHEM., ROSEG. and PETZOLDTK. PAKHOMOV S. V., RAPOPORTZ. Ts., SINELNIKOV V. M., ENTZIANG., VONCOSSARTG., SINGERW., SAMARDJIEV D. and NE~TOROV G. SINGERW., BREMERJ., HOFFMANN P. and TAUBENHE~M J. SOLAR-GEOPHYSICAL DATA
1979
The post-storm ionisation enhancements in the midlatitude D-region. HHI-STP Report 9. Berlin. Beilage znr Berliner Wetterkarte. Amtsblatt des Instituts fiir Meteorologie der Freien Universitlt Berlin SO 12/90 2.8.90. Absorption and morphology of the lower ionosphere. Bulg. Acad. Sci. Sofia, 219 pp. (in Bulgarian). J. atmos. terr. Phys. 41, 1051.
1986
Bulg. geophys. J. 12,40 (in Russian)
1987
Gerlands Beitr. Geophys. 96, 352.
1990
Solar-Geophysical Data. Prompt reports, U.S.A. National geophys. data center, Boulder. NN545-548. J. atmos. terr. Phys. 49, 777.
WILLIAMSL. R., WATKINSG. W., BLIX T. A., THRANEE. V., ENTZIANG., VONCOSSARTG., GREISIGER K. M., SINGERW., TAUBENHEIM J., FRIEDRICH M., HALL C. M., KATANJ. R., LASTOVICKA J., DELA MORENAB. A., PAKHOMOVS. V., RANTA H., RAPOPORTZ. Ts., SINELNIKOV V. M., SAMARDJIEV D., NESTOROV G., SAUERH. H. and STAUNINGP.
1990
1987
Pergamon
Pkysics, Vol. 56. Nos 13114, pp. 1923-1931, 1994 Copyright 0 194 Elsevier Science Ltd
Printed IIIGreatBritain. All rightsreserved 002l-9169,‘94
0021-9169(94)EOO39-P
$7.00+0.00
Rocket electron density profiles over Volgograd, Heiss Island and Esrange during the DYANA campaign A. K. KNYAZEV*, Z. Ts. RAPOPORT,~ V. M. SINELNIKOV?and M.
FRIEDRICH$
Aerological Observatory, Dolgoprudny, Moscow, Russia; t Academy of Sciences, Moscow, Russia ; $Department of Communications and Wave Propagation, Technical University, Graz, Austria
*Central
(Received in final firm 22 Februq
1994 ; accepted 22 Februar.y 1994)
Abstract-The results of the determination of electron density (N,) profiles at Volgograd, Heiss Island and Esrange ranges are discussed. Some of thqse profiles were obtained at solar zenith angles x90”, but at times near the sunset, and others at night-time. The profiles obtained during the DYANA campaign were compared with others obtained in the past, with solar and geomagnetic indices as well as with the temperature and atmospheric circulation in the stratosphere and mesosphere. The daytime electron densities below 85 km over Volgograd do not show any appreciable connection to the temperature. An anomalous period of low electron densities observed from February to the beginning of March rather seems to be connected with the meridional and vertical components of the atmospheric wind. We can speculate that the high night-time &values at middle latitude may be considered as a manifestation of a post-storm effect. The relationship of the N,-values at higher altitudes (> 80 km) and radio wave absorption seems to be connected with the atmospheric circulation and geomagnetic activity. The I$-values in the polar cap region (Heiss Island) are below those at the same altitude in the aurora1 zone (Esrange), but higher than at middle latitudes (Volgograd). The hi,-values over Heiss island seem to be connected with the geomagnetic activity and the meridional component of atmospheric circulation ; the thermal control of the D-region cannot be excluded.
1. INTRODUCTION
but most of them were launched near sunset; four rockets were launched at x > 90”. All profiles obtained at x < 90” were reduced to x = 88” to compare the absolute values of N,. The normalization is carried out using the expressions given by BELIKOVICH et al. (1983),
Twenty-nine rockets were launched at the different ranges for determination of the electron density N, of the lower ionosphere during the DYANA campaign. The NC-values were determined by different techniques. The data obtained were compared with the data characterizing the geophysical situation during the experiments. N(~) profifes obtained from rocket launchings at other times are shown for comparison. The measured data and their interpretation are presented below for each of the respective rocket launch sites, together with the technique employed.
2. 2. I.
EXPERIMENTAL DATA AND THEIR
N,(h) = N,(h) (COSx)~‘~’
k(h) = Aces ~36O”j, where N, (h) is the electron density profile, obtained at the solar zenith angle (observed and recalculated), N,,(h) is the electron density profile at x = O”, with the following constants :
ANALYSIS
E~ectrost~t~~probe technique
A = 0.9,
2.1.1. vo/olgograd range (48” 41’ N, 44” 21‘ E). Fourteen rockets of the type MlOOB were launched from the Volgograd range during the experimental phase of the DYANA campaign to determine the N,-profiles ; in addition, twp rockets were launched on 3 and 10 January and two rockets were launched on 21 and 28 March 1990. The dates of the launchings, the times and the solar zenith angles (x) are listed in Table 1. We can see that 14 rockets were launched at x < 90”,
B = 80.0 km,
C = 131.9 km.
Figure 1 shows the electron densities between 50 and 85 km in the time period from 5 January to 25 March 1990, no~alized to x = 88” on the basis of 14 rocket launchings. The numbers on the curves denote the electron densities (cms3), and the small arrows on the abscissa indicate the rocket launchings. We note the considerable variability of the N,-values from day to day. A reduction of the N,-values at altitudes above
1923
1924
A. K.
KNYAZEV et al.
so 14, ,lk 5 1015202530 Jan
ibb4
I41 ICI
5 101520251
5 10152025
Feb 1990
Mar
Fig. 1. Altitude-time development of the electron density over Volgograd. The N.-values are normalized to a constant solar zenith angle, x, of 88”. The numbers on the curves denote the electron density values (cm-‘). Arrows indicate the dates of rocket launchings (electrostatic probe technique).
75 km takes place during the second IO-day period in January; at the same time the electron density increases below 75 km. We can see a general tendency of decreasing NC-values after 20 January, but there are periods when NC increases at some altitudes at the same time. These periods are from 22 to 31 January at 80-85 km, from 22 to 25 January at 768 1 km, and from 29 to 31 January at 66-77 km. Low N,-values have persisted all through the second half of February. The NC-values at all altitudes increase after 5 March 1990. It is interesting to compare the variations of the N,values with geomagnetic and solar activity as well as with the temperature and atmospheric dynamics at stratospheric and mesospheric altitudes. Figure 2 shows the geomagnetic activity index A, and the solar activity index F,“,,. It is difficult to find any relationship between A, and F10,7,on the one hand, and the NC-values, on the other. This again confirms the wellknown fact that geomagnetic and solar activity indices correlate poorly at middle latitudes in winter when the correlation is made on a day-to-day basis. We suppose that the increase of the N,-value in March in the altitude region 55-83 km was an effect of considerable solar and geomagnetic activity. A proton event took place on 19 March (it began at 07.05 UT, with a maximum of 140 particles cm-* SK’ sr-’ of
Ionospheric electron density profiles
1925
IO 60 50 40 z 30 20 10 0
5
10 15 20 Jan
25 30 5
10 15 20 25 1 5
Feb 1990
10 15 20 25 30
Mar
Fig. 2. The indices of geomagnetic activity A, and solar activity F,, , from January to March 1990.
greater than 10 MeV at 08.00 UT) ; two geomagnetic storms occurred on 12 and 20 March. The A,-index was more than 70 on 21 March (SOLAR-GEOPHYSICAL DATA, 1990). In contrast, a similar period of enhanced geomagnetic activity in the second half of February coincided with a period of very low NC-values at the altitudes under consideration. The consideration of the altitude-time cross-section at 2&80 km from January to March 1990 (KOKIN et al., 1994) shows that three marked warmings took place in the upper stratosphere : in the middle of January, in February and in March (peak temperatures were observed on 20-25 March). At the same time in January and March the temperature increased in the mesosphere (7080) km) ; from 10-20 February, during the warming in the upper stratosphere, a cooling took place in the mesosphere. This supports the conclusion by ENTZIAN et al. (1971) that the mesospheric temperature varies in antiphase with that of the stratosphere. A comparison of Fig. 1 with the altitude-time temperature cross-section (KOKIN et al., 1994) confirms the conclusion drawn by OFFERMANNet al. (1979) that temperature is not the main factor which determines the variations of electron density in the mid-latitudinal lower ionosphere. The altitude-time pictures of variations of the zonal and meridional components of the wind velocity in the stratosphere and mesosphere over Volgograd are shown by KOKIN et al. (1994). We can see that the westerly wind dominates at all the altitudes considered. It reached 100 m s-’ between 40 and
60 km during the DYANA campaign ; the mesospheric wind velocities are from 10 to 80 m s-‘. There is large day-to-day variability of the wind. The mesospheric zonal velocity reached its maximum at the end of February and early March. The zonal wind velocity decreased to zero and reversed in the last lo-day period of January and at the beginning of February. At the same time, the NC-values decreased. The mesospheric westerly wind velocity increased at the end of February and at the beginning of March. This enhancement of the wind velocity coincides with the enhancement of the wind velocity at higher altitudes (NAUJOKAT et al., 1990), but a corresponding enhancement of the electron density at altitudes of 70& 80 km cannot be seen. The velocity of the meridional component shows great variability ; for example, at altitudes from 75 to 80 km it varies from -45 to + 35 m SC’. It should be noted that the long period of decreasing electron density, at altitudes 60-85 km, during February to the beginning of March (rocket launchings from 14 February to 5 March) is anomalous : the N,values at these altitudes are the lowest amongst those observed during the corresponding geophysical conditions in 1981-1989. This decrease seems to be connected with the vertical component of the wind velocity, v. The v-values were calculated by the method proposed by IVANOVA et al. (1990) ; it is based on rocket data of the temperature and horizontal wind variations. During this period the direction of v in the mesosphere was always upwards. This decrease of N,-
1926
A. K.
KNYAZEV et al.
012345678910 t
WY)
I
I
102
103
N
1
(e ~rn-~)
Fig. 3. NC-profiles obtained at night over Volgograd on 3 January (profile l), 15 January (2), 17 January (3), 28 March 1990 (4) and the mean night-time profile calculated from the data obtained under quiet geomagnetic conditions in January-December 1981-1989 by the same technique (x = loo”, F,07 i 150, profile 5). In the upper part of the inset is presented the manifestation of the post-storm effect in the night-time winter electron density ; the dots represent the data of 1981-1989, the circles refer to the launch of 3 January 1990. The lower part of the inset presents the average variation of the A,-index during geomagnetic disturbances.
values seems to be connected also with the meridional component of the wind velocity, which was southerly during the period under consideration (KOKIN et al., 1994). Figure 3 shows four N(h)-profiles, obtained at x > 90”, as well as a mean profile calculated from the results of 28 rocket launchings, which were carried out in January and February of 1981-1989 under quiet geomagnetic conditions. The horizontal bars show the 99% confidence intervals calculated on basis of 13-28 N,-values. Profiles 2 and 3 differ from the mean profile very little, but profiles 1 and 4 depart from them considerably. It is possible that the difference of the fourth profile from the mean is connected with the solar zenith angle (x = 91”)-night-time conditions may not yet have fully set in at the altitudes under consideration. Besides, the geophysical conditions preceding this rocket launching were very disturbed. The post-storm event, following the geomagnetic storm which began 5 days prior to the rocket launch of 3 January (SOLAR-GEOPHYSICAL DATA, 1990), might well be the cause of the enhancement of the
night-time electron density at that time. The significance of the post-storm effect for the winter nighttime ionization was shown earlier on the basis of the limited MAP/WINE data set (PAKHOMOVet al., 1986). We consider this effect using the more extensive data obtained from that time and examine how the data of 3 January fit into the whole picture. The analysis technique is described below. We considered the time sequence of N,-values at 80 km and the geomagnetic situation (A,-index) of the preceding 10 days. If during this period there was a day with A, > 24, this day was marked as a key day (zeroday) and the day when the N,-value was determined marked by corresponding figures from 0 to 9. Afterwards all the A, and N, data were combined into one figure. Thus, some modification of the superposed epoch technique was used. The results of the analysis are shown in the inset of Fig. 3; A,-values decrease smoothly from the key day. At the same time the N,values (log N,) decrease to the second day, increase to the fifth day and decrease afterwards. The result of the launch of 3 January agrees fairly well with the dependence obtained on the basis of the whole data determined by the electrostatic probe during nighttime conditions in winter seasons from 1981 to 1989. This effect is analogous to the effects observed earlier in radio wave absorption (LAUTER et al., 1977; N~STOROV, 1986) or in data obtained by the partial reflection technique (SINGER et al., 1987), but the cited data were obtained during the whole daytime, and at twilight. 2.1.2. Heiss Island range (80” 37’ N, 58’ 03’ E). Eleven NC-profiles were obtained during the period from 10 January to 14 March 1990 by MlOOB rockets launched from the Heiss Island range. Table 2 presents the dates and the times of the rocket launches as well as the solar zenith angles. Figure 4 presents the altitude-time section of N,values over Heiss Island during the DYANA campaign. All profiles were obtained for polar night conditions (x > 90”). It is evident that the N,-value variability at Heiss Island is less than at Volgograd. Comparison with solar activity (Fig. 2) does not reveal any correlation of F,,, with N,. At first sight there is also no positive correlation between N, and A,. However, calculations show that the correlation coefficient r(N,, AJ is positive ( >O.S) over the whole altitude range (Fig. 5). This result indicates the role of the incoming fluxes of energetic charged particles for electron density production in the polar cap. Comparison of the N,-values with the altitude-time variabilities of the velocities of the zonal and meridional winds (KOKIN et al., 1994) does not show any clear correlation between N,-values and the values and
1927
Ionospheric electron density profiles Table 2. List of rocket launches from Heiss Island during the DYANA campaign Date 1990
IO Jan.
17 Jan.
31 Jan.
Time UT x
16.22 117”
1505 112”
15.05 109”
5 Feb. 15.05 99”
7 Feb. 19.05 114”
12
21
28
7
12
14
Feb. 15.05 105”
Feb. 16.10 104”
Feb. 15.05 99”
March 15.05 97”
March 15.05 95’
March 15.05 94’
6&I 5
f 11 1 1 1 10 15 20 25 30
ff 5
Jan
A 1 I+ 1 +I 10 15 20 25 1 Feb 1990
If 5
IN 1 t 10 15 20 25 Mar
1 30
Fig. 4. The altitude-time variation of nocturnal NC-values over Heiss Island. The designations are the same as in Fig. 1.
directions of these wind components, but the correlation coefficient between the deviations of the N,values from the regression line N,(A,) and the meridional component of the wind velocity at 80 km is 0.6. This result can be considered as evidence for the significance of the southerly meridional wind in the electron production over Heiss Island. The altitude-time development of the temperature over Heiss Island during the DYANA campaign is presented by KOKIN et al. (1994). Unfortunately, the temperature data were generally obtained below 75 km whereas the N,-profiles begin above that height. It is therefore difficult to draw any conclusion about the influence of the mesospheric temperature on the electron density. Nevertheless, it is possible to note some influence of the temperature regime on the electron density distribution. Indeed, the stratospheric warming in the second half of January was accompanied by a noticeable cooling in the mesosphere, near 70 km. From 15 to 17 January the temperature decreased from - 74 to - 113°C attaining
the lowest values of the temperature observed during the winter period under consideration ; at the same time the N,-values decreased. Some increase of N,values was accompanied by the temperature increase in the mesosphere at the end of January. The most noticeable warming in the higher stratosphere (4060 km) was observed on 7 February; the temperature reached +44”C. At the same time the temperature decreased in the region above 65 km. The lowest N,values during the whole DYANA period were observed on 7 February. There is a tendency for a simultaneous variation of the N, and temperature values at mesospheric altitudes afterwards. At the same time two minor warmings in the higher stratosphere on 19 February and during the period from 7 to 12 March did not accompany the toolings in the mesosphere. Correlation coefficients between &values at 80 km and the mesospheric temperature at 74 km and the stratopause temperature are f0.41 and -0.66, respectively. The absolute values of the correlation
A. K. KNYAZEVet al.
1928
0-0 r (N A& Fig. 5. Correlation coefficient between the N,-values (Heiss Island) and the geomagnetic activity index A, vs. altitude.
coefficients are not large, so they can be considered as evidence for some tendency for the same relationship of electron density with temperature. At the same time this result is in agreement with the results obtained at Heiss Island during the MAP/WINE campaign (PAKHOMOV et al., 1986), when the correlation coefficients of N,-values at the mesopause region with the mesospheric temperature were +0.76. It is difficult to evaluate the significance of each mechanism (temperature and meridional wind) in the electron density production over Heiss Island during the DYANA campaign because both mechanisms acted simultaneously. Besides, this influence is not excluded during the DYANA campaign. This difference seems to explain the clearer relationship between electron density and temperature during the MAP/WINE campaign. It will be recalled that the relationship between electron density and temperature at middle latitudes was not apparent in either case. This difference seems to be connected with the larger variations of the temperature over Heiss Island. Comparison of the night-time N(h)-profiles over Volgograd (Fig. 3) with the profiles obtained at Heiss Island (Fig. 4) shows that in most cases the N,values at Heiss Island at the corresponding altitudes are higher than over Volgograd, which is naturally
N (e cm*)
Fig. 6. The N(h)-profiles obtained at night-time in Volgograd (coherent frequency technique). Profile 1 for 28 February, 2 for 5 March, 3 for 10 March, and 4 for 14 March 1990.
explained by the additional the high latitudes.
ionization
occurring
in
2.2. Coherent frequency technique : Volgograd range Four electron density profiles were obtained by this technique at the end of the DYANA campaign at night (x > 118”). Figure 6 presents these profiles. It is seen that NC-values at 8695 km on 28 February are higher than N,-values at this altitude for the other rocket launchings. For comparison of the N,(h)-profiles with radio wave absorption we used the values of absorption measured in Volgograd at 2.2 MHz (L2 J and the f-min parameter of vertical sounding ionograms. We took the mean value of the medians of fmin parameters obtained in 15 min during the period centred at the moment t (cos x = 0.2) p.m. and at t (cos x = 0.2) a.m., and the mean value of L,, (cos x = 0.2) p.m. and L,, (cos x = 0.2) a.m. as representatives values for the night between the days when these values offmin and L,,, were obtained. The from ionosondes mean _L values were determined near Archangelsk (64” 36’ N, 40” 30’ E), Moscow (55” 28’ N, 37” 19’ E) and Kaliningrad (54” 42’ N, 20” 36’ E). As an index of geomagnetic activity the daily sum of K-index for Moscow @Km) was taken. Values of
1929
Ionospheric electron density profiles Table 3. Geophysical parameters at three sites in Russia during the DYANA campaign Period 1990 2428 Feb. I- 5 March 8-12 March 10-14 March 28 Feb.-l March 5- 6 March 12-13 March 14-t 5 March
$) 47 39 26 27 41 33 24 29
Archangelsk
F,,, (MHz) Moscow
3.0 2.45 1.85 1.6 2.8 2.35 1.75 1.7
2.35 1.9 1.55 1.55 2.35 1.7 1.4 1.7
L,,,, fmln and ZKm thus determined were averaged for five days (nights) preceding the dates of the rocket launchings. These data as well as the data for the days (nights) of rocket launchings are presented in Table 3. The 5-day period before the launching on 28 February was more disturbed than the others. The same situation also prevailed for the nights when the rockets were launched. The geomagnetic activity changed in the same way as the radio wave absorption during this period. The atmospheric circulation in the mesosphere and lower thermosphere during the DYANA period has been described in detail by NAUJOKAT el al. (1990). As the measurements, especially those obtained by the Dl method, show, the launch on 28 February coincides with a period when these are strong westerly winds ; afterwards the wind ceases abruptly, and at 95 km even changes sign. Thus, the geomagnetic activity and atmospheric circulation variations are in accordance with the variations of the radio wave absorption (& fmin) and of the electron density in the upper part of N,-profiles obtained (WILLIAMS et al., 1987). We assume that the profile on 28 February was obtained in a period when winter anomalous conditions occurred in the lower ionosphere (especially at 85 km), and the profiles obtained in March corresponded with the final stratospheric warming, that is to the transition period from the winter anomalous conditions to the normal spring conditions. Figure 7a presents the profiles obtained on 28 February 1990 (profile 1) and on 20 January 1982 (profile 2). The last profile was obtained in Volgograd by the coherent frequency technique at night; profile 2 is similar to profile 1 in shape, but is somewhat lower. The NC-profile 2 is typical for the winter night when winter anomaly conditions prevail. Figure 7b presents the N,(h)-profiles obtained on 5 March 1990 (profile 3) and on 23 May 1979 (profile 4). Profile 4 was
Kaliningrad
CKm
2.35 1.7
31.2 23.8 21.8 26.0 30 23.5 30 23
1.6 1.6 2.0 1.6 1.5 1.6
obtained in summer-time when winter anomaly conditions are absent. Profiles 3 and 4 are very similar in shape, but the maximum N,-value for profile 3 is located 7 km higher than the maximum for profile 4. It should be noted that all four profiles presented in Fig. 7 were obtained during periods of high solar activity. It is difficult to compare the N,(h)-profiles obtained by the coherent frequency technique and by the electrostatic probe technique as they give electron density distributions in different altitude ranges. 2.3. Faraday rotation technique: Esrange (67” 53’ N, 21” 04’ E) One N&)-profile for the altitude range from 68 to 100 km was obtained by this technique. Figure 8 presents this profile (profile 1). The N,(h)-profiles obtained on 26 July 1990 (profile 2) and on 9 April 1991 (profile 3) are also shown in this figure. All the profiles were obtained at x > 90” ; profiles 2 and 3 were obtained at higher solar activity than profile 1. The NC-values of profile 1 exceed those of profiles 2 and 3. There is no basis to ascribe this difference to both solar and geomagnetic activity. We can suppose that this distinction is connected with the known ionospheric variability at high latitudes, and also that it is connected with the winter anomalous conditions which take place at Esrange’s latitude in March ; they are weaker in April and certainly absent in July. Esrange is situated very near the aurora1 zone. This seems to be the main cause of the enhanced electron density values compared with the N,-values obtained at the middle latitude range Volgograd and at the polar cap range Heiss Island. 3. CONCLUSIONS
Electron density profiles in the lower ionosphere obtained with rockets by electrostatic probe, coherent
A. K. KNYAZEVet al.
1930
120 -
120 -
80 -
80 -
102
2
3
57103
23
57
lo2
2
3
N (e em-3)
57103
23
57
N (e cm-3)
Fig. 7. N,-profiles obtained at night over Volgograd by the coherent frequency technique. Fig. 7a. l-28 February
1990; 2-20 January
1982. Fig. 7b. 3-5 March
80
601 10’
I 102
I 103
I 104
I 105
N (e cm-s) Fig. 8. IV,-profiles obtained at night Faraday rotation technique. Profile x = 95”; R = 104; A, = 21. Profile x = 92”; R = 186; A, = 26. Profile ~=95”;R= 188,A,=
over Esrange by the 1 for 6 March 1990; 2 for 26 July 1990; 3 for 9 April 1991; 10.
frequency and Faraday rotation techniques at Esrange, Heiss Island and Volgograd ranges are presented. The N,(h)-profiles at Volgograd were generally obtained before sunset (x = 88”), while others were obtained at night (x > 900). Comparison of the pro-
1990.4-23
May 1979.
files obtained by the electrostatic probe technique at Volgograd with the temperature in the upper stratosphere and in the mesosphere does not reveal any clear relationships. A period of anomalously low electron density, determined by the electrostatic probe technique, was observed in February, up to the beginning of March 1990. This decrease of the electron density seems to be connected with the directions of the vertical and meridional winds which were, at that time, upwards and from the south, respectively. The NC-value variability at night at middle latitudes after magnetic storms is comparatively large and approximately corresponds with the general winter variability. However, variations of the same order can sometimes be observed during periods without preceding geomagnetic storms. The geomagnetic control of such a kind seems to be only one of the winter variability factors. The rocket data on temperature and the dynamical regime of the stratosphere and mesosphere suggest that the lower ionosphere over Heiss Island during the DYANA campaign was not only under the control of geophysical factors, but also under the control of meteorological processes of the middle atmosphere. The N,-profiles obtained at Volgograd during the final stage of the DYANA campaign by the coherent frequency technique at higher altitudes than obtained by the electrostatic probe technique show that the N,-values, at 85-95 km, may be connected both with
Ionospheric electron density profiles winter anomalous conditions and with the atmospheric circulation as well with geomagnetic activity. The N,(h)-profile obtained by the Faraday rotation technique at Esrange on 6 March may be interpreted as being obtained under winter anomalous conditions : the NC-values in the D-region were found to
1931
be larger than the N,-values determined in April and July. At the same time, the NC-values determined for night conditions at Esrange, situated in the aurora1 zone, are higher than the NC-values obtained both at middle latitudes (Volgograd) and in the polar cap (Heiss Island).
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BUGAEVAI. V., BOUTKOA. I., KOKING. A., KOSHELKOV Yu. P., PEROVS. P., TARASENKO D. A., ZAKHAROVG. R., TOULINOVG. F., OFFERMANN D., BITTNERM., VONZAHN U., CHANINM. L., HAUCHECORNE A., SOULEI., SUBBARAYA B. H., GIL-OJEDAM., DELA MORENA B. A., SCHMIDLIN F. J., OYAMAK. I. and KANZAWA H. ENTZIANG., GAIGEROVS. S. and TARASENKO D. A.
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IVANOVAI. N., KOKING. A., LYSENKOE. V., PEROVS. P., ROSENFELD S. C. and CHIZHOVA. F. LAUTERE. A., BREMERJ., DETERSI. and EVERSK. NAUJOKATB., LABITZKEK., LENSCHOV R., PETZOLDK. and WOHLFARTR.-C.
1971 1991 1977
Catalogue of the electron density profiles of the middle latitude ionospheric D-region. Preprint of NIRFI N 171, Gorky, 51 p. (in Russian). J. atmos. terr. Phys., 56, 1659.
Transactions of the Academy of Sciences of the U.S.S.R. Phys. armos. Oceans 7,932 (in Russian). Met. Hydrol. 5, 39 (in Russian).
NESTOROV G.
1986
OFFERMANN D., CURTISP., CISNEROS J. M., SATRUSTECUI J., LAUCHEM., ROSEG. and PETZOLDTK. PAKHOMOV S. V., RAPOPORTZ. Ts., SINELNIKOV V. M., ENTZIANG., VONCOSSARTG., SINGERW., SAMARDJIEV D. and NE~TOROV G. SINGERW., BREMERJ., HOFFMANN P. and TAUBENHE~M J. SOLAR-GEOPHYSICAL DATA
1979
The post-storm ionisation enhancements in the midlatitude D-region. HHI-STP Report 9. Berlin. Beilage znr Berliner Wetterkarte. Amtsblatt des Instituts fiir Meteorologie der Freien Universitlt Berlin SO 12/90 2.8.90. Absorption and morphology of the lower ionosphere. Bulg. Acad. Sci. Sofia, 219 pp. (in Bulgarian). J. atmos. terr. Phys. 41, 1051.
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Bulg. geophys. J. 12,40 (in Russian)
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Gerlands Beitr. Geophys. 96, 352.
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Solar-Geophysical Data. Prompt reports, U.S.A. National geophys. data center, Boulder. NN545-548. J. atmos. terr. Phys. 49, 777.
WILLIAMSL. R., WATKINSG. W., BLIX T. A., THRANEE. V., ENTZIANG., VONCOSSARTG., GREISIGER K. M., SINGERW., TAUBENHEIM J., FRIEDRICH M., HALL C. M., KATANJ. R., LASTOVICKA J., DELA MORENAB. A., PAKHOMOVS. V., RANTA H., RAPOPORTZ. Ts., SINELNIKOV V. M., SAMARDJIEV D., NESTOROV G., SAUERH. H. and STAUNINGP.
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