The interaction of the magnetospheric–ionospheric (MI) system surrounding the Earth with the environment (solar wind) occurs in the form of a series of transient processes at different scales. The ...largest of them, magnetic storms, are obviously triggered by disturbances in the solar wind (direct driving). The role of the internal dynamics of the MI system, which is caused to a large extent by the nonlinearity and temporal delays of the loading–unloading processes of energy and particle from the solar wind into the magnetosphere, becomes more significant at smaller scales (substorms, pseudobreakups, injections, and activations). A typical dynamic state of the MI system is characterized as self-organized criticality or turbulence, which are characterized by statistical scale invariance (scaling) in the fluctuation distributions of many characteristics. The dynamics of the MI system is projected into the region of the auroral oval, the very existence of which is due to this dynamics. The space–time structure of auroral disturbances largely reflects the structure of processes in the MI plasma. The description of this structure is important both for studying the fundamental study of plasma processes and for many topical applied problems related to the propagation of radio waves in the ionosphere and vital activity at high latitudes. The paper discusses approaches and developments for constructing a model of the space–time structure of the auroral oval, based on fractal and multifractal characteristics.
The intensive polar stratospheric vortex in the Arctic that shifted to northern Europe in the winter of 2019–2020 caused low temperatures and the frequent occurrence of polar stratospheric clouds ...followed by a significant decrease in the total ozone content. Polarimetry and multi-color photometry using all-sky cameras in Lovozero (Murmansk Region, Russia, 68.0°N, 35.1°E) together with a new method of cloud field separation against the twilight background allowed for finding the light scattering characteristics related to the particle size distribution of polar stratospheric clouds. The results are compared with lidar and balloon experiments. The conditions of the appearance of visually bright polar stratospheric clouds of type I are discussed.
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•Bright polar stratospheric clouds were registered by RGB and polarization all-sky cameras.•New method of cloud separation on the twilight background is developed.•Parameters of size distribution of polar stratospheric clouds particles are found with high accuracy.
We report on simultaneous spacecraft and ground‐based observations of quasiperiodic VLF emissions and related energetic‐electron dynamics. Quasiperiodic emissions in the frequency range 2–6 kHz were ...observed during a substorm on 25 January 2013 by Van Allen Probe‐A and a ground‐based station in the Northern Finland. The spacecraft detected the VLF signals near the geomagnetic equator in the night sector at L = 3.0–4.2 when it was inside the plasmasphere. During the satellite motion toward higher latitudes, the time interval between quasiperiodic elements decreased from 6 min to 3 min. We find one‐to‐one correspondence between the quasiperiodic elements detected by Van Allen Probe‐A and on the ground, which indicates the temporal nature of the observed variation in the time interval between quasiperiodic elements. Multiсomponent measurements of the wave electric and magnetic fields by the Van Allen Probe‐A show that the quasiperiodic emissions were almost circularly right‐hand polarized whistler mode waves and had predominantly small (below 30°) wave vector angles with respect to the magnetic field. In the probable source region of these signals (L about 4), we observed synchronous variations of electron distribution function at energies of 10–20 keV and the quasiperiodic elements. In the pause between the quasiperiodic elements pitch angle distribution of these electrons had a maximum near 90°, while they become more isotropic during the development of quasiperiodic elements. The parallel energies of the electrons for which the data suggest direct evidence of the wave‐particle interactions is in a reasonable agreement with the estimated cyclotron resonance energy for the observed waves.
Key Points
Quasiperiodic VLF emissions were simultaneously detected by RBSP‐A and on the ground
Synchronous variations of energetic electron distribution function and VLF waves were observed
Probable source region of these signals was identified
The spatio-temporal dynamic of the substorm on December 24, 2014 in the interval from 16:00 to 17:00 UT was analyzed by data of large observational complex: magnetometers data by the Scandinavian ...network and by the longitudinal chain of the Russian auroral stations, the auroral dynamics in Apatity and data of THEMIS satellites. During the interval under study the THEMIS-E and THEMIS-D satellites were located in the midnight sector of the magnetosphere at r ~8.5–10.3 RE and then passed over Siberia toward to Kola Peninsula. We show that the first substorm disturbances in the magnetosphere were in the region between the THE and THD satellites, and, according ground-based observations, it was projected to near Amderma station. Despite a sparse observational network in Siberia, the substorm intensification was possible to trace from the point of the origin at the longitude ~80°E to the Scandinavia region at the longitude ~30°E. Our estimates of the propagation velocities of the westward traveling surge (WTS) and so-called “auroral horn” (the arc ahead WTS) confirmed the values, obtained in the previous works. The occurrence of several structures of substorm in aurora (first small, localized auroral arc; beads structure in the auroras and the auroral horn) manifestates the propagation of the disturbances from the onset region to the West. It is shown also, that the fronts of dipolarization (DFs) and injection of energetic electrons in the magnetosphere were accompanied by activations of auroras: the brightening of arcs, the breakup and the appearance of WTS over Apatity.
•Simultaneously observations by the THEMIS, by the aurora and magnetic disturbances.•Analysis of the propagation of the disturbances from the onset region to the West.•Several precursors of substorm in aurora were registered.•Dipolarization fronts and injection of energetic electrons in the magnetosphere.•Simultaneously observations of sudden intensification in aurora.
Various subauroral optical features have been studied by analyzing data collected during periods of geomagnetic disturbances. Most events have been typically found at geomagnetic latitudes of 45–60°. ...In this study, however, we present a red arc event found at geomagnetic 68° north (L ≈ 7.1) in the Scandinavian sector during a period of geomagnetically quiet conditions within a short intermission between two high‐speed solar wind events. The red arc appeared to coincide with a pseudo breakup at geomagnetic 71–72°N and a rapid equatorward expansion of the polar cap. However, the red arc disappeared in approximately 7 min. Simultaneous measurements with the Swarm A/C satellites indicated the appearance of the red arc at the ionospheric trough minimum and a conspicuous enhancement of the electron temperature, suggesting the generation of the arc by heat flux. Since there are meaningful differences in the red arc features from already‐known subauroral optical features such as the stable auroral red (SAR) arc, we considered that the red arc is a new phenomenon. We suggest that the ephemeral red arc may represent the moment of SAR arc birth associated with substorm particle injection, which is generally masked by bright dynamic aurorae.
Key Points
An ephemeral red arc appeared at 68° MLat (L ≈ 7.1) for 7 min coinciding with a pseudo breakup at 71–72° MLat
Swarm A/C measurements identified the red arc location at the trough minimum with a localized enhancement of the electron temperature
The ephemeral red arc may represent a moment of SAR arc birth
Tsallis nonextensive statistical mechanics (or
q
-statistics) has been used for the first time to study pulsating auroras, which are regularly observed in the auroral ionosphere during geomagnetic ...disturbances. For systems in which long-range interactions, such as ionized gas or plasma, take place and whose dynamics are determined primarily by long-range electromagnetic forces, it can be expected that nonadditive and nonextensive thermostatistic principles can characterize their macroscopic behavior. In this paper, we argued that pulsating auroras exhibit nonextensive properties and can be described, among other things, by
q
-statistics. We have also demonstrated that the non-extensive parameter
q
correlates well with the flatness index and with the scaling index, which indicates the applicability of this approach for auroral glow. Thus,
q
-statistics can be used to analyze phenomena in the high-latitude region of the Earth.
The possibility of evaluating the energy spectra of precipitating electrons which form rayed auroral structures has been substantiated. The data of triangulation observations by equipment recording ...radiation in a wide range of wavelengths (380–580 nm) have been used. A technique for calculating the height profiles of deposition energy from the height profiles of the volume emission rate recorded by the receiving equipment. The energy spectra of precipitating electron fluxes responsible for the formation of rayed structures in auroras have been reconstructed. It is shown that the energy spectra of the precipitating electron flux can be approximated by the sum of two electron fluxes having a power-law energy spectrum and a Maxwellian energy distribution. It has been suggested that radiant structures in auroras are formed due to the discharge of electrons into the ionosphere, which have a power-law energy distribution.
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Statistical properties noted earlier from ground-based television observations on Spitsbergen are found in the activation of aurora detected by the all-sky camera in Lovozero. These properties are ...areas with a power-law distribution in the probability density of the characteristics of auroral spots. Considerable sensor noise makes it impossible to extend the distributions to smaller scales than those published earlier.
The altitudes of typical auroral forms observed on the polar and equatorial boundaries of the auroral oval are analyzed. Triangulation based on data from two pairs of cameras located in Apatity and ...Barentsburg is used. The cameras in pairs are separated by ~4 km. The energy of precipitating electrons is estimated in dynamics for different auroral structures.
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