The sudden increase of fluxes of quasi-trapped energetic electrons under the Earth’s radiation belt (ERB) has remained a puzzling phenomenon for decades. It is known as enhancements of forbidden energetic electrons (FEEs). The FEE enhancements are occasionally observed by low-Earth orbit NOAA/POES satellites. Previously, no strong correlation was established between FEEs and geomagnetic activity, while external control of FEE occurrence by solar activity and interplanetary parameters was revealed on a long time-scale. Two important questions are still open: (1) key parameters of the mechanism and (2) solar wind drivers or triggers. In the present study we conducted detailed analysis of three FEE events that occurred during the greatest geomagnetic storms, which dramatically affected space weather. The FEE enhancements occurred under northward IMF and, thus, Bz and convection electric fields could have been neither driver nor trigger. We found that an abrupt and significant change in solar wind pressure is a key solar wind driver of the FEE enhancements observed. The characteristic time of FEE injection from the inner edge of the ERB at L-shell 1.2 to the forbidden zone at L < 1.1 was estimated to be 10–20 min. In the mechanism of ExB drift, this characteristic time corresponds to the radial inward transport of electrons caused by a transient electric field with the magnitude ~10 mV/m.

The intense precipitation of energetic electrons from the Earth’s radiation belt (ERB) is one of the most important sources of ionization in the ionosphere and atmosphere. A large-scale statistical analysis is carried out of the data from continuous low-orbit satellite observations of solar-cycle variations in the flux enhancements of the ERB electrons with energy >30 keV at an altitude of 850 km, acquired from the NOAA/POES and MetOp satellites in the interval from 1998 to 2022. The basic features of artificial failures in the satellite database with high-time resolution measurements in the interval from 2014 to 2022 are found and described. Appropriate data correction is carried out. It is shown that the average annual number of days with electron flux enhancements increases rapidly within three years after the solar-cycle maximum and reaches its greatest value near the middle of the declining phase of solar activity. Then the frequency of event occurrence begins to decrease noticeably within an 8-year interval, including the minimum, rising, and maximum phases of the solar cycle. The minimum level is achieved at the maximum solar activity.

An Erratum to this paper has been published: https://doi.org/10.1134/S1990793124340050

We present the results of a statistical study of transient enhancements of electrons with energies >30 keV at low drift shells in the quasi-trapped region (forbidden zone) at the geomagnetic equator. Using data from low-altitude NOAA/POES and MetOp satellites, we have compiled a catalog of events with forbidden energetic electron (FEE) enhancements for the period from 1998 to 2023. Statistical analysis of FEE events has revealed solar-cyclic, as well as seasonal and diurnal variations in the occurrence of FEE enhancements. We have examined the correlation of the annual frequency of FEE events with solar activity, solar wind parameters, and geomagnetic activity. Strong correlations have been found with the F10.7 index of solar activity (radio emission flux) as well as with the Alfvén Mach number (solar wind parameter). An interpretation of the obtained results is proposed which is based on the mechanism of electrical drift and radial transport of electrons from Earth’s inner radiation belt to the quasi-trapped region (L<1.2). The key factor for the operation of the mechanism is the effective penetration of the electric field to low latitudes when a significant difference in the conductivity of the high-latitude ionosphere occurs in the illuminated and unilluminated sectors of local time under conditions of weakening auroral activity.

Intense fluxes of electrons from the Earth’s radiation belt (ERB) with energies of tens and hundreds of keV can penetrate to low altitudes at low latitudes outside the South Atlantic Anomaly. This region is known as a forbidden zone of quasi-trapped energetic particles. Flux enhancements of energetic electrons in the forbidden zone, so-called forbidden energetic electrons (FEE), produce significant ionization effects in the upper atmosphere at low latitudes. In this work, solar-cycle variations of the FEE enhancements with energy > 30 keV were analyzed over a 25-year period using a database of low-orbit satellites of the NOAA/POES and MetOp series. We found the highest correlations of the annual occurrence of FEE with the F10.7 solar activity index (−0.87) and the Alfven Mach number of the upstream solar wind (0.76). Using multiparameter regression analysis, a power expression was obtained with those parameters as well as with plasma beta and the interplanetary magnetic field strength with a total correlation coefficient of 0.94. The role of the conductivity of the high-latitude ionosphere in the mechanism of the penetration of ERB electrons into the forbidden zone is discussed.

We report effects in the upper high-latitude atmosphere related to the interaction of fast magnetosheath plasma streams, so-called jets, with the dayside magnetopause. The jets were observed by THEMIS mission in the dayside magnetosphere during a quiet day on 12 July 2009. It was found that the jet interaction was accompanied by strong localized compression and penetration of suprathermal magnetosheath plasma inside the dayside magnetosphere. The compression caused prominent magnetic variations with amplitudes up to 100 nT observed by ground-based magnetic networks SuperMAG and CARISMA. The magnetic variations were also visible in the geomagnetic Dst and AE indices. The jets also resulted in intense precipitation of the suprathermal ions with energies < 10 keV and energetic electrons with energies > 30 keV observed by low-altitude NOAA/POES satellites in a wide longitudinal range. The precipitations produced enhancements of ionization with an amplitude of ~1 TECU (~30% in relative units) and intensification of the ionospheric E and F1 layers as observed in the FORMOSAT-3/COSMIC misson. The enhanced ionization in the upper atmosphere might affect radio communication and navigation in the high-latitude regions. These results also provide new insight into the contribution of magnetospheric forcing to day-to-day ionospheric variability.

The intense precipitation of energetic electrons (with an energy of tens of keV) from the Earth's radiation belt (ERB) is one of the most important sources of ionization in the ionosphere and atmosphere. In this paper, we analyze the spatial distribution of electron fluxes with energies greater than 30 keV at an altitude of 850 km using the maximum amount of statistical data available today. It is found that the region of electron precipitation from the outer zone of the ERB is shifting over North America to the pole, and over Siberia to the equator. Moreover, in the region of the Brazilian magnetic anomaly (BMA), the intensity of the energetic electron fluxes and its area in the 24th solar cycle decreases compared to the 23rd cycle. Based on the analysis of the distribution of quasi-trapped electrons under the radiation belt at low latitudes confirms the mechanism of their rapid radial transfer from the outer zone of the ERB to the Earth. The results obtained are mainly related to the change in the configuration of the Earth's magnetic field, as well as to the decrease in solar and geomagnetic activity in the 24th solar cycle.

Future commercial, scientific, and other satellite missions require low-Earth-orbit (LEO) altitudes of 300–400 km for long-term successful space operations. The Earth’s radiation belt (ERB) is an inevitable obstacle for manned and other space missions. Precipitation of >30 keV energetic electrons from the ERB is one of the sources of ionization in LEO, space vehicles, in the ionosphere, and in the upper atmosphere. We show, in this work, that the area of electron precipitation from the outer ERB shifts equator-wards to Siberia. We further show a substantive decrease in the intensity of energetic electrons in the area of the South Atlantic Anomaly (SAA) from the 23rd to the 24th solar cycles. These results can be attributed to, and explained by, variations in geomagnetic activity, with a noticeable change in the configuration of the Earth’s magnetic field during the 24th solar cycle. The diminishing SAA area and electron fluxes should allow elevation of the International Space Station to higher altitudes, thereby making these altitudes accessible to relevant space missions.

Experiments on board low-Earth orbit satellites show that energetic particles (tens of keV) of the Earth’s radiation belt can penetrate to the equatorial ionosphere. Impact of the energetic particles on the upper atmosphere and ionosphere was studied for the case of the geomagnetic storm on 22 July 2009. We present changes of local ion concentration in the low-latitude ionosphere at night measured by the C/NOFS satellite at heights 400-800 km during the magnetic storm and quiet days. The ionospheric density during the storm was compared with a simultaneous observation of enhancements of 30-80 keV proton fluxes measured by the NOAA/POES satellites near the equator at height ~850 km. We suggest that ionospheric irregularities at night can be caused by effect of energetic protons.

Results of studying different-scale ionospheric irregularities on the basis of multi-instrumental data, obtained in the East Siberian region of Russia during the geomagnetic storm of May 27–28, 2017, are presented. Spatial inhomogeneities of electron density in the ionosphere were observed through data from ground-based receivers of signals of global navigational satellite systems and on the basis of direct measurements of electron density in low-orbit satellites. An intense radio aurora was seen in UHF radar data just after the initial phase of geomagnetic storm. At the same time, we recorded fluctuations of the total electron content from data of GPS receivers and the presence of E-layer irregularities by data of the ionosonde in Norilsk. The time of irregularity recording by different instruments is consistent with the spatiotemporal changes in field-aligned currents of the second zone, obtained from data of AMPERE low-orbit satellite system.

Energetic electrons (with energies of 10 to 1000 keV) from the Earth’s radiation belt (ERB) play an important role in the processes associated with the ionization of the upper atmosphere and ionosphere from the equator to high latitudes. The main sources and properties of energetic electrons at the altitudes of the ionosphere of up to 1000 km are considered. At high latitudes (more than 50°), precipitations from the outer belt are the sources of such electrons. At low latitudes, intensive fluxes of electrons appear as a result of their injection from the inner ERB. The analysis of the solar-cyclic variation of energetic electron fluxes during two solar cycles in the period from 1998 to 2018 is performed. It is shown that the maximum electron fluxes are most often observed at the declining phases of solar activity (SA), which is associated with the contribution from the recurrent geomagnetic activity. The lowest fluxes are found in the deep minimum of the SA of 2009. As a result, the energetic electron fluxes during the current, 24th, solar cycle are found to be weaker than those in the previous cycle. In addition, an anomalous shift of the position of the maximum of the outer ERB to the equator by 4° (which is equivalent to a distance of 400 km) which is not predicted by the standard model is observed over Siberia. Apparently, this is associated with an acceleration of the change in the geomagnetic field in this region.

This paper reports energetic (>30 keV) electron flux enhancement at L<1.2 measured by the NOAA/POES satellites and relate it to the transient injection of magnetosheath plasma into the dayside magnetopause region, which is measured by the THEMIS satellite, and global geomagnetic pulses, which are measured by ground INTERMAGNET magnetometers and GOES satellites. The authors propose a scenario of possible association between these dayside magnetopause phenomena with the deep injection of >30keV electrons at L<1.2 by the penetration of localized electric field.

We study two events of structured Pc1 waves (pearls) observed by CARISMA magnetometers during a period of quiet magnetic (Kp ~1) and solar wind conditions on 1 August 2008. Bursts of proton precipitations and electromagnetic ion‐cyclotron waves were simultaneously observed by NOAA/POES and GOES satellites at dayside. Apparent correspondence was found between ground pearl pulsations and magnetospheric compressions observed by GOES and THEMIS satellites. We have found the Pc1 wave splitting into very close subfrequencies (within 0.1 Hz) that can be explained by weak magnetospheric compressions. The compressions are caused by pressure pulses originated from transient foreshock and interplanetary magnetic field discontinuities observed upstream of the bow shock by the THEMIS‐C probe. Thus, the observed pearls are compression‐related Pc1 waves generated under transient foreshock conditions.

The main chemical reactions that lead to formation of the nonequilibrium two-temperature plasma and highly excited Rydberg complexes are considered. A special attention is given to l-mixing reaction responsible for the formation of quantum resonance properties for radio wave propagation medium. A detailed analysis of the influence of Rydberg states to the behavior of GPS signals in D and E layers of the ionosphere is presented. It is shown that the transition frequencies between the excited states of orbitally degenerate Rydberg complex are resonant with respect to the carrier frequencies of GPS. That is why these states are the main cause of the GPS signal distortion. The mechanism of GPS signal delay in D and E layers is also discussed.

Abstract. An unusual event of deep injections of u003e 30 keV electrons from the radiation belt to low L shells (L 1.2) in midnight-dawn sector occurred during nonstorm conditions on August 1, 2008. Using THEMIS observations in front of the bow shock, we found transient foreshock conditions and rotational discontinuities passing the subsolar region at that time. These conditions resulted in generation of fast magnetosheath plasma jets and penetration of the magnetosheath plasma into the magnetosphere as were observed by the THEMIS probes after approaching the magnetopause. The magnetosphere responded to variations in the IMF orientation by magnetic field perturbations. Magnetic records at ground-magnetometers of INTERMAGNET provided evidence of a global geomagnetic response in the form of geomagnetic pulses from the equator to middle latitudes. The earliest response was found at low latitudes in the predawn sector. We propose a scenario of possible association between dynamical foreshock in the subsolar region, magnetosheath plasma jets and the deepest injections of the u003e 30 keV electrons at L 1.2 at the midnight-dawn sector.