Red Arcs Research Articles

The Scrambling Index of Two-colored Wielandt Digraph

A digraph is primitive provided there is a positive integer k such that for each pair of vertices u and v there exist walks of length k from u to v and from v to u. The scrambling index of a primitive digraph D is the smallest positive integer k such that for each pair of vertices u and v in D there is a vertex w such that there exist walks of length k from u to w and from v to w . A two-colored digraph is a digraph each of whose arc is colored by red or blue. In this paper we generalize the notion of scrambling index of a primitive digraph to that of two-colored digraph. We define the scrambling index of a two-colored digraph D (2) to be the smallest positive integer h+ l over all pairs of nonnegative integers (h, l) such that for each pair of distinct vertices u and v there is a vertex w with the property that there are walks form u to w and from v to w consisting of h red arcs and l blue arcs. For two-colored Wielandt digraph on n 4 vertices we show the scrambling index lies on the interval (n 2 3n + 3, n 2 2n + 2).

Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

Abstract. Research results about planetary-scale auroral distributions are presented in a historical retrospective, beginning with the first "maps of isochasms" – lines of equal visibility of auroras in the firmament (Fig. 2) – up to "isoaurora maps" – lines of equal occurrence frequency of auroras in the zenith (Fig. 4). The exploration of auroras in Russia from Lomonosov in the 18th century (Fig. 1) until the start of the International Geophysical Year (IGY) in 1957 is shortly summed up. A generalised pattern of discrete auroral forms along the auroral oval during geomagnetically very quiet intervals is presented in Fig. 5. The changes of discrete auroral forms versus local time exhibit a fixed pattern with respect to the sun. The auroral forms comprise rays near noon, homogeneous arcs during the evening, and rayed arcs and bands during the night and in the morning. This fixed auroral pattern is unsettled during disturbances, which occur sometimes even during very quiet intervals. The azimuths of extended auroral forms vary with local time. Such variations in the orientation of extended forms above stations in the auroral zone have been used by various investigators to determine the position of the auroral oval (Fig. 9). Auroral luminosity of the daytime and nighttime sectors differ owing to different luminosity forms, directions of motion of the discrete forms, the height of the luminescent layers, and the spectral composition (predominant red emissions during daytime and green emissions during the night). Schemes that summarise principal peculiarities of daytime luminosity, its structure in MLT (magnetic local time) and MLat (magnetic latitude) coordinates, and the spectral composition of the luminosity are presented in Figs. 15 and 19. We discuss in detail the daytime sector dynamics of individual discrete forms for both quiet conditions and auroral substorms. The most important auroral changes during substorms occur in the nighttime sector. We present the evolution of conceptions about the succession of discrete auroral forms and their dynamics during disturbance intervals. This ranges from Birkeland's polar elementary storms, over the prospect of a fixed auroral pattern up to the auroral substorm model. The classic schemes of the spatial distribution and motion of discrete auroral forms during single substorms are shown in Fig. 20 (expansive and recovery phases) and Fig. 21 (creation, expansive and recovery phases). In this review we discuss various models of bulge formation, in particular as a result of new formation of arcs about 50–100 km poleward of previously existing auroral structures (Fig. 24). Discrete steps in the development of an expanding bulge are separated by 1–3 min from each other. The model of successive activations confines only to a ~40° longitudinal portion of the magnetotail (Fig. 28). We consider differences in the development of single substorms and substorms during magnetic storms. The structure and dynamics of auroras during steady magnetospheric convection (SMC) periods are dealt with in Sect. 8. A generalised scheme of the auroral distribution during SMC periods is shown in Fig. 34. Separate sections describe discrete auroras in the polar cap (Sect. 5), and the diffuse luminosity equatorward of the auroral oval (Sect. 9). Visual observations of diffuse auroral forms at midlatitudes suggest that the whole latitudinal interval between the auroral oval and the stable auroral red (SAR) arc is filled up with diffuse luminosity. SAR arcs with intensities of several tens of Rayleigh enclose systematically the region of diffuse luminosity; they are positioned at the border of the plasmasphere.

Imaging magnetospheric boundaries at ionospheric heights

AbstractAn all‐sky imager (ASI) records atmospheric emissions from zenith to low on the horizon at all azimuths, a region typically spanning millions of square kilometers. Each pixel (with its unique elevation, azimuth, and emission height) can be mapped along B‐field lines to the equatorial plane of the magnetosphere. Auroral and subauroral structures and boundaries seen in emission within the ionosphere‐thermosphere (I‐T) system can thus be related to source regions. For a midlatitude site, this I‐T to inner magnetosphere connection typically falls within the L = 2–5 earth radii domain. In this study, we present the first case of a stable auroral red (SAR) arc observed from three widely spaced ASI sites (Europe, North America, New Zealand). SAR arcs are produced during the main and recovery phases of a geomagnetic storm, with emission driven by heat conduction from a very specific location in the magnetosphere—the L value where the plasmapause and the inner edge of the ring current overlap. Using three‐site observations, we show that this boundary can be followed for 24 consecutive hours. Simultaneous observations made by three satellites in the Defense Meteorological Satellite Program (DMSP) show that the lowest latitude peak in electron temperature can be used to map the same boundary. A key structure of the inner magnetosphere that cannot be observed continuously from sensors orbiting within the magnetosphere is made continuously visible to ground‐based optical systems via effects caused by the drainage of small amounts of ring current energy into the I‐T system.

Observation and modeling of magnetospheric cold electron heating by electromagnetic ion cyclotron waves

A cold electron heating event associated with electromagnetic ion cyclotron (EMIC) waves is observed and modeled. The observational data of particles and waves are collected by the Time History of Events and Macroscale Interactions during Substorms spacecraft at magnetic local time 17.0–17.2. During this event, intense He+ band EMIC waves with the peak frequency 0.25 Hz are excited, corresponding to the observed phase space density (PSD) of distinct anisotropic ions. Meanwhile, substantial enhancements in energy flux of cold (1–10 eV) electrons are observed in the same period. The energy flux of electrons below 10 eV is increased by several to tens of times. We use a sum of kappa distribution components to fit the observed ion PSD and then calculate the wave growth rate driven by the anisotropic hot protons. The calculated result is in good agreement with the in situ observation. Then, we investigate whether the excited EMIC waves can transfer energy to cold electrons by Landau resonant absorption and yield electron heating. Using the typical Maxwellian distribution for cold electrons, we evaluate the wave damping rates resulted from the cold electrons in gyroresonance with EMIC waves. The simulating results show that the strong wave growth region in the He+ band induced by anisotropic ions corresponds to the strong wave damping region driven by cold electrons. Moreover, cold electrons can be heated efficiently at large wave normal angles. The current results provide a direct observational evidence for EMIC‐driven cold electron heating—a potential mechanism responsible for stable auroral red arc.

Thermally excited 630.0 nm O(1D) emission in the cusp: A frequent high‐altitude transient signature

We highlight why 630.0 nm auroral emissions excited by thermal electrons are expected to be significant in the cusp and are occurring more often than generally recognized. We note conditions when they are likely to occur and provide a simple formula to calculate the altitude discriminated (R/km) and line‐of‐sight integrated 630.0 nm intensity (kR). The formula is applied to incoherent scatter radar data near the cusp to produce 2‐D maps of thermal red line aurora. We estimate when the thermally excited red aurora should be negligible or not, for given electron density (Ne), electron temperature (Te), and exospheric temperature (Tn) conditions. Sensitivity to Te dominates that to Tn and Ne. We test these formulas against radar and all‐sky imaging photometer data for 2 days. The time/space agreement, as transient strong red arcs pass over the cusp, confirms detection of a thermal 630.0 nm aurora in ~400–450 km altitude, twice the height (4 times the area) conventionally assumed for 630.0 nm emissions. Among many potential uses for this technique is application to the long‐standing question of the degree to which magnetic reconnection events contribute to the net magnetic flux entering the polar cap. We conclude that it is more often than now recognized and provide a tool and guidelines to facilitate improvement over present underestimates.

Italian all‐sky imager tracks auroral red arcs over Europe

During geomagnetic storms, stable auroral red (SAR) arcs reach down from polar latitudes, their faint glow stretching equatorward of the traditional auroral oval. Invisible to the naked eye, SAR arcs are an upper atmospheric occurrence produced by the emission of light from oxygen atoms in the thermosphere. The excitation of the ionospheric oxygen that produces SAR arcs is caused, in turn, by the conduction of heat from the magnetospheric ring current. Advances in camera optics, including more sensitive sensors and highly specific filters, have allowed researchers to track the occurrence of SAR arcs, opening a window into the dynamics of the inner magnetosphere.

Imaging space weather over Europe

We describe the introduction of the first all‐sky imaging system for low‐light‐level optical observations of the disturbed ionosphere over mid‐latitude Europe. Using 6300 Å auroral emissions that come from the 200–400 km altitude range, we demonstrate that sub‐visual optical patterns spanning the European continent can be obtained from a single site in Italy. Pilot observations during the 26–27 September 2011 geomagnetic storm show that the diffuse aurora's low latitude boundary can be used to find where the poleward wall of the ionospheric trough is located. This relates directly to regions of radiowave disruptions caused by the precipitation of energetic particles from the magnetospheric plasma sheet that move to lower latitudes during space weather events. Images of stable auroral red (SAR) arcs can be used to track the magnetospheric ring current and plasmapause location, a second region of radiowave interference. Comparisons with ground‐based and satellite observations of the ionosphere during the same storm demonstrate how ASI images reveal the lowest energy components of magnetospheric input to the ionosphere‐thermosphere system. Such observations can be used, potentially, for both now‐casting of storm effects spanning Europe, and for retrospective validation of existing models of space weather impacts at sub‐auroral locations.

A stable auroral red arc over Europe

Using a new all-sky-imaging system, M Mendillo, C Barbieri, J Baumgardner, J Wroten, G Cremonese and G Umbriaco observed two distinctive types of aurora over London and western Europe on the night of 26–27 September 2011, including the first ground-based image of a stable auroral red arc over Europe.

Photographic observation of a natural fourth-order rainbow

We report what is believed to be the first photographic recording of a quaternary rainbow in nature. It appears on the Sun side of the sky with its red arc at a radius of about 45° from the Sun. The original pictures have been subjected to various forms of image processing to reveal the tertiary rainbow as well as the quaternary rainbow, which are separated by only a few degrees with their colors reversed and their red arcs adjacent to each other.

Shock aurora: Ground‐based imager observations

This paper studies dayside shock aurora forms and their variations observed by the ground‐based all‐sky imager (ASI) in Svalbard on 30 November 1997. The interplanetary shock arrived at Earth when Svalbard was at ∼1120 magnetic local time. The ASI detected an auroral intensification by a factor of 2 or more in both green and red line emissions within 5 min after the shock arrival. The intensified green emissions were mainly diffuse aurora on closed field lines. They were latitudinally below and adjacent to the red aurora, which was mainly in the form of arcs and beams along the magnetic east‐west direction. The diffuse aurora expanded equatorward and eastward, and its intensity exceeded the red arcs that were at ∼5 kR. We confirmed that the eastward propagating diffuse aurora was actually moved antisunward along the oval, which suggests that the antisunward propagating shock aurora seen in space is mainly diffuse aurora. The intense diffuse aurora could be caused by wave instabilities led by a temperature anisotropy and/or caused by an enlarged loss cone. After the shock arrival, the detected low‐latitude boundary of the cusp moved equatorward at a speed of ∼18 km min−1. As a result, the cusp meridional width was doubled from ∼0.8° to 1.6° in latitude in 10 min. This finding implies that a low‐latitude reconnection occurred during the compression. In this study the auroral signatures and speculated mechanisms are consistent with those revealed by in situ particle and wave observations from FAST and DMSP.

Pre-Carboniferous, episodic accretion-related, orogenesis along the Laurentian margin of the northern Appalachians

Abstract During the Early to Middle Palaeozoic, prior to formation of Pangaea, the Canadian and adjacent New England Appalachians evolved as an accretionary orogen. Episodic orogenesis mainly resulted from accretion of four microcontinents or crustal ribbons: Dashwoods, Ganderia, Avalonia and Meguma. Dashwoods is peri-Laurentian, whereas Ganderia, Avalonia and Meguma have Gondwanan provenance. Accretion led to a progressive eastwards (present co-ordinates) migration of the onset of collision-related deformation, metamorphism and magmatism. Voluminous, syn-collisional felsic granitoid-dominated pulses are explained as products of slab-breakoff rather than contemporaneous slab subduction. The four phases of orogenesis associated with accretion of these microcontinents are known as the Taconic, Salinic, Acadian and Neoacadian orogenies, respectively. The Ordovician Taconic orogeny was a composite event comprising three different phases, due to involvement of three peri-Laurentian oceanic and continental terranes. The Taconic orogeny was terminated with an arc–arc collision due to the docking of the active leading edge of Ganderia, the Popelogan–Victoria arc, to an active Laurentian margin (Red Indian Lake arc) during the Late Ordovician (460–450 Ma). The Salinic orogeny was due to Late Ordovician–Early Silurian (450–423 Ma) closure of the Tetagouche–Exploits backarc basin, which separated the active leading edge of Ganderia from its trailing passive edge, the Gander margin. Salinic closure was initiated following accretion of the active leading edge of Ganderia to Laurentia and stepping back of the west-directed subduction zone behind the accreted Popelogan–Victoria arc. The Salinic orogeny was immediately followed by Late Silurian–Early Devonian accretion of Avalonia (421–400 Ma) and Middle Devonian–Early Carboniferous accretion of Meguma (395–350 Ma), which led to the Acadian and Neoacadian orogenies, respectively. Each accretion took place after stepping-back of the west-dipping subduction zone behind an earlier accreted crustal ribbon, which led to progressive outboard growth of Laurentia. The Acadian orogeny was characterized by a flat-slab setting after the onset of collision, which coincided with rapid southerly palaeolatitudinal motion of Laurentia. Acadian orogenesis preferentially started in the hot and hence, weak backarc region. Subsequently it was characterized by a time-transgressive, hinterland migrating fold-and-thrust belt antithetic to the west-dipping A–subduction zone. The Acadian deformation front appears to have been closely tracked in space by migration of the Acadian magmatic front. Syn-orogenic, Acadian magmatism is interpreted to mainly represent partial melting of subducted fore-arc material and pockets of fluid-fluxed asthenosphere above the flat-slab, in areas where Ganderian's lithosphere was thinned by extension during Silurian subduction of the Acadian oceanic slab. Final Acadian magmatism from 395– c . 375 Ma is tentatively attributed to slab-breakoff. Neoacadian accretion of Meguma was accommodated by wedging of the leading edge of Laurentia, which at this time was represented by Avalonia. The Neoacadian was devoid of any accompanying arc magmatism, probably because it was characterized by a flat-slab setting throughout its history.

Astronomical sky spectra from the 29-31 October 2003 geomagnetic superstorms: Observations of O+(2Do-4So) and other emissions

[1] High-resolution spectra of the night sky at near-equatorial latitudes have been obtained with the Ultraviolet and Visual Echelle Spectrograph on the 8.2 m Kueyen telescope, European Southern Observatory, Cerro Paranal, Chile, during the 29–31 October 2003 geomagnetic superstorms. These spectra show indications of both thermospheric and ionospheric disturbance. Numerous emission features observed in these spectra have behaviors that correlate with the negative magnitude of the disturbance storm time index (Dst), a measure of the ring current influence on equatorial magnetic field strength. Specifically, the intensity of the optically forbidden and rarely observed O+(2Do–4So) doublet lines at 372.6 and 372.9 nm increases with decreasing Dst and have profiles that often possess unusual morphology. Also observed on nights with strong geomagnetic activity is sustained emission after twilight from both the N2+ first negative system 0-0 band at 391.4 nm and the He(3p3Po–2s3S) 388.9 nm line. The intensities of permitted neutral oxygen lines nominally arising from electron radiative recombination are suppressed during active periods relative to levels measured during quiescent periods. The pattern of emission in these spectra may reflect the manifestation of a variety of storm time phenomena, including negative ionospheric storms, energetic neutral auroras, and stable auroral red arcs, and indicates substantial energy deposition at high altitudes.

Relationship of the diffuse aurora and SAR arc dynamics to substorms and storms

Investigation results of a diffuse aurora (DA) and stable auroral red (SAR) arc dynamics based on spectrophotometric observations at the Yakutsk meridian (199°E geomagnetic longitude) are presented. The relationship of an equatorward extension of DA in the 557.7 nm emission to a substorm growth phase during the magnetospheric convection intensification after the turn of IMF B Z to the south is shown. The formation of SAR arc during the substorm expansion phase is investigated. The association of SAR arc dynamics with the development of asymmetric ring current (substorm injection) during the main phase of a storm is analyzed. It is shown how the pulsating precipitations of energetic ring current particles develop in the outer plasmasphere based on photometric observations.

Self‐consistent model of magnetospheric ring current and propagating electromagnetic ion cyclotron waves: 2. Wave‐induced ring current precipitation and thermal electron heating

This paper continues presentation and discussion of the results from our new global self‐consistent theoretical model of interacting ring current ions and propagating electromagnetic ion cyclotron waves (Khazanov et al., 2006) currently developing in NASA Marshall Space Flight Center. To study the effects of electromagnetic ion cyclotron wave propagation and refraction on the wave induced ring current precipitation and heating of the thermal plasmaspheric electrons, we simulate the May 1998 storm. The main findings after the simulation can be summarized as follows. First, the wave induced ring current precipitation exhibits quite a lot of fine structure and is highly organized by location of the plasmapause gradient. The strongest fluxes of about 4 × 106 (cm2 s sr)−1 are observed during the main and early recovery phases of the storm. The very interesting and probably more important finding is that in a number of cases the most intense precipitating fluxes are not connected to the most intense waves in simple manner. The characteristics of the wave power spectral density distribution over the wave normal angle are extremely crucial for the effectiveness of the ring current ion scattering. Second, comparison of the global proton precipitating patterns with the results from RAM (Kozyra et al., 1997a) reveals that although we observe a qualitative agreement between the localizations of the wave induced precipitations in the models, there is no quantitative agreement between the magnitudes of the fluxes. The quantitative differences are mainly due to a qualitative difference between the characteristics of the wave power spectral density distributions over the wave normal angle in RAM and in our model. Third, the heat fluxes to plasmaspheric electrons caused by Landau resonate energy absorption from electromagnetic ion cyclotron waves are observed in the postnoon‐premidnight MLT sector and can reach the magnitude of 1011 eV/(cm2 s). The Coulomb energy degradation of the RC H+ and O+ ions maximizes at about 1011 eV/(cm2 s) and typically leads to electron energy deposition rates of about 2 × 1010 eV/(cm2 s) which are observed during two periods, 32–48 hours and 76–86 hours after 1 May, 0000 UT. The theoretically derived spatial structure of the thermal electron heating caused by interaction of the ring current with the plasmasphere is strongly supported by concurrent and conjugate plasma measurements from the plasmasphere, ring current, and topside ionosphere (Gurgiolo et al., 2005). Finally, the wave induced intense electron heating has a structure of the spot‐like patches along the most enhanced density gradients in the plasmasphere boundary layer and can be a possible driver of the observed but still not explained small‐scale structures of enhanced emissions in the stable auroral red arcs.

A very bright SAR arc: implications for extreme magnetosphere-ionosphere coupling

Abstract. In contrast to the polar aurora visible during geomagnetic storms, stable auroral red (SAR) arcs offer a sub-visual manifestation of direct magnetosphere-ionosphere (M-I) coupling at midlatitudes. The SAR arc emission at 6300 Å is driven by field-aligned magnetospheric energy transport from ring current/plasmapause locations into the ionosphere-thermosphere system. The first SAR arc was observed at the dawn of the space age (1956), and the typical brightness levels and occurrence patterns obtained from subsequent decades of observations appear to be consistent with the downward heat conduction theory, i.e., heated ambient F-layer electrons excite oxygen atoms to produce a spectrally pure emission. On very rare occasions, a SAR arc has been reported to be at brightness levels visible to the naked eye. Here we report on the first case of a very bright SAR arc (~13 kilo-Rayleighs) observed by four diagnostic systems that sampled various aspects of the sub-auroral domain near Millstone Hill, MA, on the night of 29 October 1991: an imaging spectrograph, an all-sky camera, an incoherent scatter radar (ISR), and a DMSP satellite. Simulations of emission using the ISR and DMSP data with the MSIS neutral atmosphere succeed in reproducing the brightness levels observed. This provides a robust confirmation of M-I coupling theory in its most extreme aeronomic form within the innermost magnetosphere (L~2) during a rare superstorm event. The unusually high brightness value appears to be due to the rare occurrence of the heating of dense ionospheric plasma just equatorward of the trough/plasmapause location, in contrast to the more typical heating of the less dense F-layer within the trough.

Self‐consistent model of magnetospheric ring current and propagating electromagnetic ion cyclotron waves: Waves in multi‐ion magnetosphere

The further development of a self‐consistent theoretical model of interacting ring current ions and electromagnetic ion cyclotron waves (Khazanov et al., 2003) is presented. In order to adequately take into account wave propagation and refraction in a multi‐ion magnetosphere, we explicitly include the ray tracing equations in our previous self‐consistent model and use the general form of the wave kinetic equation. This is a major new feature of the present model and, to the best of our knowledge, the ray tracing equations for the first time are explicitly employed on a global magnetospheric scale in order to self‐consistently simulate the spatial, temporal, and spectral evolution of the ring current and of electromagnetic ion cyclotron waves. To demonstrate the effects of EMIC wave propagation and refraction on the wave energy distribution and evolution, we simulate the May 1998 storm. The main findings of our simulation can be summarized as follows. First, owing to the density gradient at the plasmapause, the net wave refraction is suppressed, and He+‐mode grows preferably at the plasmapause. This result is in total agreement with previous ray tracing studies and is very clearly found in presented B field spectrograms. Second, comparison of global wave distributions with the results from another ring current model (Kozyra et al., 1997) reveals that this new model provides more intense and more highly plasmapause‐organized wave distributions during the May 1998 storm period. Finally, it is found that He+‐mode energy distributions are not Gaussian distributions and most important that wave energy can occupy not only the region of generation, i.e., the region of small wave normal angles, but all wave normal angles, including those to near 90°. The latter is extremely crucial for energy transfer to thermal plasmaspheric electrons by resonant Landau damping and subsequent downward heat transport and excitation of stable auroral red arcs.

Empirical model of variations in the OI 630 nm emission. 1. Intensity

The empirical model of variations in the atomic oxygen emission intensity depending on different heliogeophysical conditions such as nighttime, lunar time, lunar phase age, season, year, and solar activity level during the 11-year cycle, as well as on cyclic aperiodic activity variations, level of geomagnetic disturbances, and their manifestations in the form of midlatitude subauroral red arcs, has been developed based on the long-term measurements of this emission intensity.

Low‐latitude auroras observed in Japan: 1999–2004

From routine observations by means of highly sensitive all‐sky cameras and tilting‐filter photometers, a total of 20 low‐latitude aurora events in Japan were identified during the high solar activity period of 1999–2004. This indicates that the invisible‐level auroras appear rather frequently in the northern sky of Japan during magnetic storms. These auroras are characterized by an enhancement in red (630.0 nm) emissions in the northern sky during magnetic storms, probably at geomagnetic latitudes higher than ∼40–50°. We show examples of stable auroral red (SAR) arcs, which are typically observed during the recovery phase of storms. We also found several red aurora events that occurred at the initial phase of magnetic storms. Intensifications as well as equatorward motion of the auroras were observed in association with storm time substorms. Green line emissions (557.7 nm) were often enhanced (∼1 kR) not only in the northern sky but also in the whole sky. Some auroras show weak enhancements (∼10 R) of N2+1N (427.8 nm) in the northern sky in the morning hours. We discuss possible causes of these emissions in light of magnetospheric disturbances and thermospheric dynamics.

Small-scale structure on the poleward edge of a stable auroral red arc

Here we present all-sky images of a stable auroral red arc collocated with the low-density trough. Small-scale, dynamic structure is observed on the poleward edge of the arc that may be caused by a crossed density/temperature gradient or by a collisional Kelvin-Helmholtz shear-flow instability in conjunction with a sufficient density gradient.

Ракурсні умови спостережень середньоширотних червоних дуг та полярних сяйв на станції Академік Вернадський

Середньоширотні червоні (SAR) дуги на станції Академік Вернадський можуть спостерігатися низько над горизонтом в напрямі на південний полюс при помірній геомагнітній активності та поблизу зеніту під час магнітних бур. При екстремальних магнітних збуреннях в районі станції можуть з’являтися середньоширотні полярні сяйва. Для типових висот SAR-дуг і сяйв над поверхнею Землі розглянуто співвідношення між їх можливою кутовою висотою над горизонтом, просторовою відстанню та інтервалом геомагнітних оболонок, які охоплюються при оптичних спостереженнях цих об’єктів на станції. Розрахунки показують, що візирна лінія практично перпендикулярна до геомагнітних силових ліній в області світіння на великому інтервалі відстаней. Це дає переваги в дослідженні висотного розподілу інтенсивності авроральних емісій.