Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.izmiran.rssi.ru/magnetism/Feldstein_2012/PDF/389.pdf Äàòà èçìåíåíèÿ: Wed Mar 11 16:54:10 2009 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 21:18:01 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: viking 2

Ann. Geophysicae 17, 37±41 (1999) ñ EGS ± Springer-Verlag 1999

Comment on `Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles' by A. G. Yahnin et al.
Y. I. Feldstein1 and Y. I. Galperin
1

2

Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation, Troitsk, Moscow Region, 142092, Russia Tel: +7 095 334 02 96; Fax: +7 095 334 01 24; e-mail: lgromova@izmiran.troitsk.ru 2 Space Research Institute of RAS, Moscow, Russia

The purpose of this comment is to clarify our views on the mapping problem incorrectly presented in the work by Yahnin et al. (1997) (hereafter, Y97), and also to indicate some diculties in this study which can lead to further misunderstanding of this and related problems. In Y97 case studies are described of relative positions of discrete auroral arcs from ground-based all-sky camera data, and low-altitude satellite data on energetic particle isotropisation boundaries (IB) measured by the similar TIROS satellites NOAA-6 and NOAA-7. On this basis they attempted to compare some schemes of mapping the magnetospheric plasma domains, and in particular, the central plasma sheet (CPS) with its neutral sheet (NS), and the plasma sheet boundary layer (PSBL) in the tail, to dierent regions of the nightside auroral luminosity. We cannot agree with the formulation in Y97 of our mapping concepts and scheme, which were described in several papers, in particular, in Feldstein and Galperin (1985, 1993) (further, FG85 and FG93), and Galperin and Feldstein (1991, 1996) (further, GF91 and GF96). Consequently, we must clarify the dierence between our mapping scheme and that of Lyons et al., (1988) and Lyons (1992) as was described in Y97 in their Discussion section. In page 956 of Y97 we read: ¼in contrast to the view of Feldstein and Galperin, and in agreement with the ®ndings of Elphinstone et al. (1995), discrete arcs are sometimes found at high latitudes, very close to the sharp decrease in the electron energy ¯ux which is certainly related to the outermost part of the plasma sheet¼'. This statement is not only wrong, it is internally contradictory because it claims that, according to our view, the polar part and the boundary of the oval of discrete auroral forms (in particular, and rather often, auroral arcs) do not contain discrete arcs! We can only remind readers of our papers, those cited already and others on the subject, where during moderate and active conditions the whole length of the auroral oval of discrete forms, from its inner boundary-equatorial auroral arc, as far as its outermost part, is projected to the tail current sheet. We are sure that our texts are clear

enough on this issue as can be seen by their analysis by other researchers (see e.g., Hones et al., 1996). It was indeed surprising to read about such a `contrast' in the Discussion section of Y97 while even in their Introduction section (page 944) it is correctly stated that in the papers FG85 and GF91 we have `mapped the discrete participation into the rest of the plasma sheet, situated tailwards of the trapping boundary¼'. This misconception is further developed by Y97 in their Fig. 4 which was intended to schematize the dierence noted, or `contrast'. In particular their Fig. 4b entitled `After Feldstein and Galperin (1985)' does not represent our view as is claimed in Y97. Our own scheme of our concepts that summarize the dynamics of magnetospheric structure between very quiet and strongly disturbed conditions was published in FG93 as Fig. 7 exactly in the same format as in Fig. 4 in Y97. Astonishingly, instead of using this ®gure, Yahnin et al. (1997) made another one which misinterprets our results. To demonstrate this we reproduce here Fig. 1 together with Fig. 7 from FG93, and Fig. 4 from Y97. In the ®gure schematic 2D cross sections of the magnetosphere are shown (not to scale) for the midnight meridian. It can be seen that in our real scheme, during extended, very quiet intervals, the equatorial steady auroral arc of the oval is located at, or close to, the stable trapping boundary for energetic electrons. Thus it projects as far as, or close to, the inner edge of the crosstail current in the plasma sheet while the rest of the plasma sheet till the distant neutral line (DNL) projects to the polar diuse auroral zone (PDAZ). Our scheme also includes the change in the magnetospheric structure during disturbed periods or magnetospheric substorms. During moderately strong disturbance the whole widened near-midnight auroral oval of discrete forms projects to the tail current sheet from its inner edge (often projected to an equatorial arc) to the new neutral line (NNL), or a plasmoid. The NNL probably corresponds to an active intense polar auroral arc, or band, at the polar auroral bulge, or polar edge of the oval. The


38

Y. I. Feldstein and Y. I. Galperin: Comment on Magnetospheric source region of discrete auroras

Fig. 1a±c. Schematic presentation (not to scale) of the magnetospheric tail plasma domain for the midnight meridian cross section and some structural features of the magnetotail, a in the interval of quiet auroras and b during substorm expansion phase according to Feldstein and Galperin (1993). c Schematic presentation of dierent

views to the source region of auroras from Yahnin et al. (1997). Field line 1 is a dipole-like magnetic ®eld, line 2 corresponds to inner edge of the current sheet, line 3 corresponds to inner edge of PSBL, and line 4 marks the outer edge of the plasma sheet

PDAZ is also present during moderately disturbed periods, but shrinks in latitude. Its projection to the plasma sheet can extend as far as the DNL (see discussion later in the text). During the expansion phase maximum, the bright auroral band, considered to be the projection of the DNL, can be at the polar cap boundary, so that the PDAZ shrinks, or temporally disappears (Feldstein and Elphinstone, 1992). Apparently the existence of the PDAZ adjacent to, but poleward from the oval of discrete forms, was not recognized in Y97 (see later). We may remind readers that there exists a really important contrast between the scheme advocated by Lyons and his co-workers, as well as by some other researches (it is reproduced in Y97 in their Fig. 7 in its upper part, and again here in Fig. 1), and the scheme advocated by us. This contrast lies in the projection of the nightside auroral oval to the tail: to the PSBL according to the former scheme, and to the CPS

according to ours. This mapping is critical for the implied location of the equatorial arc projection in the tail plasma sheet and thus of the auroral substorm onset region in the magnetosphere. In the former scheme it was supposed to occur at distances $50±100 Re, i.e. in the distant tail, and thus is related to the PSBL. In our scheme this distance, from many arguments, was evaluated as located somewhere between $5±15 Re (depending on activity level), i.e. near the inner boundary of the tail current sheet which we identify with the inner boundary of the CPS (FG85, CF91). This latter view (not entirely new, see FG85) is now con®rmed by multitude of in situ measurements and apparently is fully accepted by the magnetospheric community (see Kennel, 1992, 1995). Another diculty in Y97 concerns the relative position of the bright auroral arc, or band, at the oval polar boundary, and the VDIS-2 events (velocity dispersed ion structures of type 2) discovered by


Y. I. Feldstein and Y. I. Galperin: Comment on Magnetospheric source region of discrete auroras inferred

39

Kovrazhkin et al. (1987), and Zelenyi et al. (1990) at the polar edge of the auroral precipitation, or the polar cap boundary. Y97 claim on page 944 that bright polar auroral arc collocates with VDIS-2, and build their interpretation on this premise. Here their neglect of the existence of the PDAZ is crucial. This structural part of the auroral luminosity was discovered and studied by Yevlashin (1961, 1964, 1968), Eather (1969) and Eather and Mende (1972) from ground optical observations; by Whalen et al. (1977), from airborne auroral observations. Then it was analyzed in detail from satellite soft electron spectral measurements as a distinct structural feature in auroral precipitation by Valchuk et al., (1979) and by other researchers (see detailed discussion in FG85, GF91 and Newell et al., 1996 for quantitative de®nitions). It will be interesting to see how long it will take for Yahnin et al. (1997) to assess the existence and signi®cance of the PDAZ poleward from the oval of bright discrete forms, the ®nding of which their own Polar Geophysical Institute played the leading role. One case where the two structural features, the polewardmost bright auroral acr, and a VDIS-2 structure, were supposed to overlap, indeed was noted in Elphinstone et al., (1995), but it is by no means typical. Observations from the AUREOL-3 show that the VDIS-2 structures overlap with the PDAZ, not with the polar bright auroral band. Detailed statistical results on VDIS-2 structures (99 cases) were presented by Bosqued et al. (1993) (see especially their Fig. 6). They show that a VDIS-2 structures ``is always observed poleward of and adjacent to the region of discrete electron precipitation'' (page 19187). In average the VDIS-2 structures are located within $1° of latitude inward from the polar cap boundary, but the average location of the polewardmost inverted-V is still further 1±2° equatorword. Similar results were published from several other satellites (See, for example, Saito et al., 1992, from AKEBONO, de la Beaujardiere et al., 1994, and Sotirelis et al., 1997 from DMSP). This means that typically the VDIS-2 lies outside of the oval of discrete forms, as was described, for example, in GF91. These data, to our view, are inconsistent with the neglect of the PDAZ at the times of VDIS-2 presence in the ``new'' scheme proposed in Y97, and with the collocation of VDIS-2 with the polewardmost auroral arc, or band, as was supposed in Y97. Also they missed the PDAZ in their presentation of our results. The NOAA satellites particle data, through not fully presented in Y97, seem to be consistent with the appearance of the PDAZ, or the soft zone, in the cases considered. It seems to us not less signi®cant that in many cases the VDIS-2 structures, if interpreted as the velocity-®lter eect from a point source in a constant electric ®eld, have their extrapolated origin(for in®nite velocity) just at, or near, the polar edge of the PDAZ, i.e. at the polar cap boundary (see, GF91, GF96). This could imply widely dierent radial distances to the origin in the far tail of the bright polar auroral band and of VDIS-2, and thus their dierent sources. By contrast, the polar bright auroral band of the double oval can sometimes consist

of a series of parallel arcs, not of a single arc, with their multiple structure similar to multiple arcs of the origin in the inner part of CPS as was demonstrated by Echim et al. (1997). Thus, there can exist sometimes a morphological similarity of the polewardmost auroral band and multiple auroral features throughout the oval of discrete forms, which could suggest their common physical nature within the CPS, at least for such particular cases. There are also some minor remarks concerning the Y97 paper. Their main result apparently is (Page 945): `...all auroral arcs found just poleward of isotrophic boundary of >30 keV electrons'. We must note that this result is not new. Evidently, the boundary of stable trapping for the outer belt electrons of >30 keV during steady conditions is one and the same with the IB for electrons of these same energies in the near-midnight sector, at least, the most equatorial IB (see, for example, Burrows and McDiarmid, 1972; GF91). The near collocation of this boundary with the equatorial boundary of the auroral oval of discrete auroral forms was ®rst shown statistically by Feldstein and Starkov (1970), Ackerson and Frank (1972); Feldstein (1974), Vorobiev et al. (1976), Lui et al. (1977), Lui and Burrows (1978), and then from case studies including satellite measurements of particle spectra by Valchuk et al. (1979). This collocation was again demonstrated and used by FG85, FG93, and in other papers on the subject, for example, in GF91, GF96. Indeed, it was the key argument for the mapping scheme where the diuse auroral belt and respective diuse precipitation equatorward from the oval are projected to the external part of the outer radiation belt; it is obvious that the region within the trapping zone cannot be mapped to the CPS. The association of the most equatorial auroral arc of the oval at nightside with the inner boundary of the tail current sheet and non-adiabatic ion scattering was also discussed long ago, e.g., in a model by Galperin et al. (1992). Thus this experimental result obtained in Y97, as concerns the diuse auroral belt and equatorial part of the auroral oval, from our point of view, while not new, can be considered as an additional con®rmation of the mapping scheme advocated by us for a long time. This seems to be accepted also in Y97. The last remark concerns the magnetospheric terminology often used which can be misleading especially to students entering the ®eld who are not always aware of past discussions and further clari®cations, and thus can take the terminology used in recent papers as a guidance. We believe that there are now obsolete terms the usage of which must be abandoned, and a new terminology elaborated. One such term is `low-altitude CPS' for the region which concides with the diuse precipitation within the outer radiation belt, i.e. within the boundary of stable trapping, that has nothing to do with the real CPS in the tail. Another such term is `lowaltitude BPS' which sometimes is still used for the structured precipitation above the auroral oval, the main part of which at nightside is projected to the tail CPS. Some proposals for terminology was described in GF96 and by Newell et al. (1996), and we shall be


40

Y. I. Feldstein and Y. I. Galperin: Comment on Magnetospheric source region of discrete auroras

grateful for critical remarks and/or other such proposals for a discussion at forthcoming scienti®c meetings. In summary we conclude that: 1. The results of case studies of the relative locations of equatorial auroral arc and isotropy boundary (IB) for energetic electrons in Y97 are in full agreement with the mapping scheme of FG85, GF91 (as con®rmed in Y97). Thus we cannot ®nd any ``contrast'' between the experimental data presented in Y97 with our views. 2. The middle part of Fig. 4 in Y97 entitled `After Feldstein and Galperin, 1985' signi®cantly distorts our concepts described in that and other our papers on the subject because according to our real scheme: a. The region of bright discrete auroral forms, the auroral oval, from its equatorial to its polar arcs, or bands, is mapped to the tail current sheet; b. Our scheme, in contrast to the statement by Y97, re¯ects the important dierences in the magnetospheric tail structure for dierent activity levels. In our scheme, with a change of the activity level, the boundary between diuse and discrete aurora shifts in latitude while remains close to the stable trapping boundary for the outer belt electrons (>30 keV), or the IB for these electrons; c. According to the Fig. 1a, during magnetically quiet intervals, a bright steady auroral arc or band is mapped on the near-Earth's part of the plasma sheet. Poleward from it, a soft precipitation appears (or, a soft zone according to Makita et al., 1985). It leads to weak, and variable, auroral features, mostly in the red line emission, within the polar diuse auroral zone (PDAZ); they map to the distant plasma sheet, possibly, as far as the DNL. d. During substorm expansion, the auroral oval is mapped in the plasma sheet between its inner edge and the NNL. During the expansion phase maximum the PDAZ can shrink, so that auroral oval polar border can appear at the DNL. 3. The scheme proposed in Y97 (their Fig. 4) neglects some important observational facts: a. The existence of the PDAZ as a distinct structure of auroral precipitation located poleward from the bright auroral band or, inverted-V; b. Consistent results from many satellites which show that the VDIS-2 ion precipitation structures nearly always are located within the PDAZ, i.e. outside the polar bright auroral band of the oval. In our opinion these misconceptions in Y97, as well as some others, are partly due to non-critical utilization of obsolete terminology still persistent in the literature. Abbendum. We are somewhat disappointed by the Reply by Yahnin et al. (1998) (Y98). The crucial point of our scheme concerning the PDAZ and its mapping, remains unanswered by Y98. Without this principal part of our concepts, as well as with other points indicated

herein, it is hard to say that they are ``reproduced correctly'' as claimed in Y98. As to our identi®cation of the boundary of stable trapping for >30 keV outer belt electrons with the IB for the electrons of these same energies, not only for us but also for many researchers in the ®eld with whom we have consulted, they appear one and the same. However the particle instruments on which Y97 base their study were directed vertically upward, not along the magnetic ®eld line, at 850 km. This makes them look at a side of the loss cone, and sometimes partly outside it for electrons>30 keV above the auroral oval where the inclination of the magnetic ®eld can be $75±80°. Thus, as stated in Y97 (page 945), these detectors ``register the particles both inside and outside the loss cone''. This can exaggerate the tendency to isotrophy for electrons>30 keV which, due to enhanced pitch angle scattering and ®eld-aligned potential drops at middle and low auroral altitudes, sometimes can have a rather narrow loss cone at 850 km. The loss cone for energetic protons is wider and not so aected by the inclination. If the authors of Y97, Y98 are able to show, for electrons >30 keV, a systematic dierence between the IB and the stable trapping boundary in the nearmidnight sector, this will be a new and signi®cant result. However for that an apparatus will be needed with a better pitch angle coverage and angular resolution than that used in Y97.
Acknowledgements. This work was supported in part by the RFBR grants 96-05-66279 for YIF, and 97-02-16333 for YIG, and by the INTAS grants 95-0932 for YIF, and 96-2346 for YIG.

References
Ackerson, K. L., and L. A. Frank, Correlated satellite measurements of low-energy electron precipitation and ground-based observations of a visible auroral arc, J. Geophys. Res., 77, 1128± 1136, 1972. Bosqued, J.-M., AUREOL-3 results on ion precipitation, Phys. Scr., 18, 158±166, 1987. Bosqued, J.-M., M. Ashour-Abdalla, M. El Alaoui, V. Peroomjan, L. M. Zelenyl and C.P. Escoubet, Dispersed ion structures at the poleward edge of the auroral oval: low-altitude observations and numerical modeling, J. Geophys. Res., 98, 19181±19204, 1993. Burrows, J. R., and I. B. McDiarmid, Trapped particle boundary regions, in Critical Problems of Magnetospheric Physics, Ed. Dyer, E. R., IUCSTP Secretariat c/o National Academy of Sciences, Washington D.C., USA, 83±104, 1972. de la Beaujardiere, O., L. R. Lyons, J. M. Ruohoniemi, E. FriisChristensen, C. Danielsen, F. J. Rich, and P. T. Newell, Quiettime intensi®cations along the poleward auroral boundary near midnight, J. Geophys. Res., 99, 287±298, 1994. Eather, R. H., Latitudinal distributions of auroral and airglow emissions: the ``soft'' auroral zone, J. Geophys. Res., 74, 153± 159, 1969. Eather, R. H., and S. B. Mende, High latitude particle precipitation and source regions in the magnetosphere, in MagnetosphereIonosphere interactions, ed. Folkestad, K., Universitets-Forlaget, Oslo, 139±154, 1972. Echim, M., M. Giobanu, O. Balan, A. Blagau, O. Marghitu, E. Georgescu, Y. I. Galperin, N. V. Jorjio, T. M. Muliarchik, A. L. Kotikov, E. M. Shishkina, and O. A. Troshichev, Multiple


Y. I. Feldstein and Y. I. Galperin: Comment on Magnetospheric source region of discrete auroras inferred current sheets in double auroral oval observed from the MAGION-2 and MAGION-3 satellites, Ann. Geophysicae., 15, 412±423, 1997. Elphinstone, R. D., D. Hearn, L. L. Cogger, J. S. Murphee, A. Wright, I. Sandahl, S. Ohtani, P. T. Newell, D. M. Klumpar, M. Shapshak, T. K. Potemra, K. Mursula, and J. A. Sauvaud, The double oval UV auroral distribution 2. The most poleward arc system and the dynamics of the magnetotail, J. Geophys. Res., 100, 12093±12102, 1995. Feldstein, Y. I., Night-time aurora and its relation to the magnetosphere, Ann Geophysicae, 30, 259±272, 1974. Feldstein, Y. I., and R. D. Elphinstone, Aurorae and the large-scale structure of the magnetosphere, J. Geomagn. Geolectr., 44, 1159±11742, 1992. Feldstein, Y. I., and Y. I. Galperin, The auroral luminosity structure in the high-latitude upper atmosphere: its dynamics and relationship to the large-scale structure of the Earth's magnetosphere, Rev. Geophys. Space Phys., 23, N3, 217±275, 1985. Feldstein, Y. I., and Y. I. Galperin, An alternative interpretation of auroral precipitation and luminosity observations from the DE, DMSP, AUREOL, and Viking satellites in terms of their mapping to the nightside magnetosphere, J. Atmos. Terr. Phys., 55, 105±121, 1993. Feldstein, Y. I. and G. V. Starkov, The auroral oval and the boundary of closed ®eld lines of geomagnietic ®eld, Planet. Space Sci., 18, 501±508, 1970. Galperin, Y. I. and Y. I. Feldstein, Auroral luminosity and its relationship to magnetospheric plasma domains, in Auroral Physics, Eds. Meng, C.-I., M. J. Rycroft, and L. A. Frank, Cambridge UP, Cambridge, 207±222, 1991. Galperin, Y. I., and Y. I. Feldstein, Mapping of the precipitation regions to the plasma sheet, J. Geoman Geolectr., 48, 857±875, 1996. Galperin, Y. I., A. V. Volosevich, and L. M. Zelenyi, Pressure gradient structures in the tail neutral sheet as ``Roots of the Arcs'' with some eects of stochasticity, Geophys. Res. Lett., 19, 2163±2166, 1992. Hones, E. W., M. F. Thomsen, G. D. Reeves, L. A. Weiss, D. L. McComas, and P. T. Newell, Observational determination of magnetic connectivity of the geosynchronous region of the magnetosphere to the auroral oval. J. Geophys. Res., 101, 2629± 2640, 1996. Kennel, C. F., The Kiruna conjecture: the strong version, SUBSTORMS 1, Proc. of the First Int. Conference on substorms, Ed. Mattok, C., ESA SP-335, Noordwijk, 599±601, 1992. Kennel, C. F., Convection and substorms, in Paradigms of Magnetospheric Phenomenology, Oxford University Press, New York, 1995. Kovrazhkin, R. A., J. -M. Bosqued, L. M. Zelenyi, and N. V. Jorjio, Reconnection and plasma acceleration evidences manifestation at 0.5 million km distance in the Earth's magnetic tail, Letts. ZETP (in Russian), 45, 377±380, 1987. Lui, A. T. Y., and J. R. Burrows, On the location of auroral arcs near substorm onset, J. Geophys. Res., 83, 3342±3348, 1978. Lui, A. T. Y., D. Venkatesan, C. D. Anger, S.-I. Akasofu, W. J. Heikkila, J. D. Winningham, and J. R. Burrows, Simultaneous

41

observations of particle precipitation and auroral emissions by the ISIS-2 satellite, J. Geophys. Res., 82, 2210±2226, 1977. Lyons, L. R., Inferences concerning the magnetospheric source region for auroral breakup, SUBSTORMS 1, Proc. First International Conference on Substorms, Kiruna, Sweden, Ed. Mattok, C., ESA SP-335, Noordwijk, 257±261, 1992. Lyons. L. R., and D. S. Evans, An association between discrete aurora and energetic particle boundaries, J. Geophys. Res., 89, 2395±2400, 1984. Lyons, L. R., J. F. Fennell, and A. L. Vampola, A general association between discrete auroras and ion precipitation from the tail, J. Geophys. Res., 93, 12932±12940, 1988. Makita, K., C.-I. Meng, and S.-I. Akasofu, Temporal and spatial variations of the polar cap dimension inferred from the precipitation boundaries, J. Geophys. Res., 90, 2744±2752, 1985. McDiarmid, I. B., J. R. Burrows, and E. E. Budzinski, Average characteristics of magnetospheric electrons (150 eV to 200 keV) at 1400 km, J. Geophys. Res., 80, 73±79, 1975. Newell, P. T., Y. I. Feldstein, Y. I. Galperin, and C. I. Meng, The morphology of nightside precipitation, J. Geophys. Res., 101, 10737±10748, 1996. Satio, Y., T. Mukai, M. Hirahara, S. Machida, and N. Kaya, Distribution function of precipitating ion beams with velocity dispersion observed near the poleward edge of the nightside auroral oval, Geophys. Res. Lett., 19, 2155±2158, 1992. Sotirelis, T., P. T. Newell, and C. -I. Meng, Polar rain as a diagnostic of recent rapid dayside merging, J. Geophys. Res., 102, 7151±7157, 1997. Valchuk, T. E., Y. I. Galperin, J. Crasnier, L. M. Nikolaenko, J. A. Sauvaud, and Y. I. Feldstein, Diuse auroral zone. IV. Latitudinal distribution of auroral optical emissions and particle precipitation and its relationship with the plasmasheet and magnetotail, Cosmic Res (in Russian), 17, 559±579, 1979. Vorobiev, V. G., B. V. Rezhenov, and G. V. Starkov, Relation between the location of eastward electroject, energetic electron trapping boundary, and auroras, Geomagn. Aeron. (in Russian), 16, 304±310, 1976. Whalen, J. A., R. A. Wagner, and J. Buchav, A 12-hour case study of auroral phenomena in the midnight sector: oval, polar cap, and continuous auroras, J. Geophys. Res., 82, 3529±3546, 1977. Yahnin, A. G., A. V. Sergeev, B. B. Gvozdevsky, and S. Vennerstrom, Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles, Ann. Geophysicae., 15, 943±958, 1997. Yahnin, A. G., V. A. Sergeev, B. B. Gvozdevsky, and S. Vennerstrom, Reply, Ann. Geophysicae., 16, (this issue), 1998. Yevlashin, L. S., Type A red auroras at high latitudes, Geomagn. Aeron. (in Russian), 1, 531±533, 1961. Yevlashin, L. S., On the character of auroras observed in the nearpole region, Geomagn. Aeron. (in Russian), 4, 188±189, 1964. Yevlashin L. S., On the character of auroral glow within the auroral region at periods of solar activity maximum and minimum, Ann. Geophysicae 24, 527±529, 1968. Zelenyi, L. M., R. A Kovrazhkin, and J.-M. Bosqued, Velocitydispersed ion beams in the nightside auroral zone: AUREOL-3 observations, J. Geophys. Res., 95, 12119±12139, 1990.