Guglielmi A.V., Potapov A.S.  Problems of the Pc1 magnetospheric wave theory. A review. Solar-Terrestrial Physics. 2019. Vol. 5. Iss. 2. P. 89-94. DOI: 10.12737/stp-53201910.

The Pc1 ultra low frequency electromagnetic waves (frequency range 0.2-5 Hz), also known as pearl necklace, are a unique phenomenon in near-Earth space physics. Many properties of pearls remain a mystery, despite the research of prominent cosmophysicists for more than half a century. In the proposed review, we briefly outline the main points of the so-called standard model, which is widely used to interpret Pc1. Next, we focus on the criticism of the standard model and on the identification of open problems in the Pc1 theory. The general conclusion is that it is necessary to develop new ideas outside the framework of the standard model in order to understand the processes of excitation and propagation of Pc1 waves in the Earth`s magnetosphere.

Potapov A., Dovbnya B., Klain B., Guglielmi A. Trigger Excitation of IPDP ULF Waves (Maltseva-Vinogradova Effect). In: Kocharyan G., Lyakhov A. (eds) Trigger Effects in Geosystems. Springer Proceedings in Earth and Environmental Sciences. Springer, Cham, 2019. P. 579-588. DOI: https://doi.org/10.1007/978-3-030-31970-0_61.

The Maltseva-Vinogradova effect was discovered by Soviet/Russian geomagnetologists in 1971. It consists in the fact that after pulsed injection of energetic protons from the magnetotail to the region of closed magnetic shells, frequency-modulated irregular pulsations of a diminishing period (IPDP, 0.1-5 Hz) are excited. Pulsations are generated in such a way that in the evening sector of the magnetosphere an azimuthal movement of the oscillation source at a given fixed frequency from east to west is observed. The present paper studies the effect of the westward drift of the IPDP frequency from the results of simultaneous observation of oscillations at the Mondy and Borok observatories separated in the geomagnetic longitude by 60°. Our interest is motivated, firstly, by the fact that IPDP belongs to the class of trigger events. Secondly, the interpretation of the frequency modulation of the IPDP and, in particular, the interpretation of the Maltseva-Vinogradova effect makes it possible to penetrate the essence of the whole complex of physical processes accompanying the origin and evolution of geomagnetic storms. We will demonstrate the analyzed effect on the new observational material, discuss the problems of excitation and propagation of IPDP, and point out ways of using IPDP to diagnose the magnetosphere and to predict space weather. In particular, we draw attention to the important fact that the observed properties of IPDP appear to contain useful information about the strength and possible duration of a geomagnetic storm.

Dovbnya B.V., Pashinin A.Yu., Rakhmatulin R.A. Short-term electromagnetic precursors of earthquakes. Geodynamics & Tectonophysics. 2019. Vol. 10, Iss. 3. P. 731-740.

In the study of the relationship between electromagnetic and seismotectonic processes, we analyzed the data of three observatories located at large distances, considering both latitudes and longitudes, and detected electromagnetic impulses in the frequency range from 0 to 5 Hz, which were recorded minutes before earthquakes. Detailed morphological and statistical analysis was carried out, and common and specific features were considered. Several cases are discussed to illustrate the occurrence of electromagnetic precursor signals before the recorded devastating earthquakes in Japan, China, Romania and other seismically active regions. A qualitative explanation is given for the study results.

Potapov A.S., Polyushkina T.N. Estimation of the ionosphere critical frequency without radio sounding. IEEE Transactions on Geoscience and Remote Sensing.2020. Vol. 58, Iss. 7. P. 5058-5065. DOI: 10.1109/TGRS.2020.2972011.

The frequency parameters of the ionospheric Alfven resonator (IAR) emission show a close connection with the critical frequency foF2 of the ionospheric F2 layer. However, the quantitative characteristics of the connection are unstable and can vary significantly from day to day. To overcome this instability, we propose to use a multiple regression analysis with additional factors that reflect the state of the ionosphere as predictors. On the basis of the training sample, we compute a set of regression equations using various combinations of regressors, of which we choose the most effective from the point of view of minimizing the estimate standard error. The efficiency of the obtained equations for the critical frequency estimation is checked using the control data sample. The results suggest that the proposed method makes it possible to estimate the value of the critical frequency with an accuracy of about 0.5 MHz. A proposal is made to use information on the IAR frequency structure in the development of assimilation ionospheric models.

Potapov A.S., Polyushkina T.N. Response of IAR frequency scale to solar and magnetic activity in solar cycle 24. AIMS Geosciences. 2020. V. 6. Iss. 4. P. 545-560. DOI: 10.3934/geosci.2020031.

The ionospheric Alfven resonator (IAR) is an integral element of the entire ionosphere-magnetosphere system. It plays an essential role in energy exchange and interaction between the magnetosphere and ionosphere. The parameters of this resonator reflect the state of the ionosphere. The purpose of this study was to study three types of IAR frequency modulation (daily, seasonal and solar-cyclic) and to identify their relationship with solar and magnetic activity. We used the results of magnetic observations of the IAR emission at the Mondy mid-latitude observatory for the 24th solar activity cycle from 2009 to 2019. The dependence of the difference in the neighboring harmonics frequencies (i.e., the emission frequency scale) on solar activity (the sunspot number) and on the magnetic indices Kp, Dst and AE was studied. The correlation between the frequency scale and the indices of solar and magnetic activity was investigated at different time scales by comparing the variations in daily, monthly, and annual averages. The dependence of the IAR frequency scale on solar activity turns out to be much closer than the same dependence of any of the three magnetic indices. The closest relationship is exhibited between the annual average values of the frequency scale, on the one hand, and the sunspot number and the Dst index, on the other. This result is interpreted as a demonstration of the cumulative effect of solar activity on the state of the ionosphere and, first of all, on the electron concentration in the F2 region of the ionosphere.

Potapov A.S., Guglielmi A.V., Dovbnya B.V. Ultra low frequency emissions ranging from 0.1 to 3 Hz in the circumpolar areas. Solar-Terrestrial Physics. 2020. Vol. 6. Iss. 3. P. 40-45. DOI: 10.12737/stp-63202006.

We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1-3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968-1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth`s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

Potapov A.S. Kinetic magnetic holes in the high speed streams during solar cycle 23. Planetary and Space Science. 2020. Vol. 192, Article 105066. DOI:https://doi.org/10.1016/j.pss.2020.105066.

One of the important elements of solar wind turbulence is the so-called "magnetic holes" (MHs), sharp temporary drops in the intensity of the interplanetary magnetic field. Using solar wind data from the ACE and Wind spacecraft, distribution and evolution of kinetic-type MHs are investigated. In particular, in the first part of this study, we examine fifteen high-speed Alfvenic streams with a high helicity value, which are mainly CIR streams. The period from 1997 to 2011 is covered, with one stream per year selected. A total of 207 kinetic MHs with duration of 3 to 129 s were detected in 15 high-speed streams with a total duration of 1004 hours. The occurrence rate of holes is about 5 events per day (0.2 per hour), which far exceeds the average frequency of MH observation in the slow wind. The median value of the MH depth is 1.52 nT, the maximum is 22.5 nT. The occurrence rate of holes monotonically increases with decreasing their duration. During the solar cycle, the probability of MH observation increases at minimum and during the early growth phase (1997–1998 and 2008–2010), reaching 0.32 events per hour. In the second part, the dynamics of MHs during their convective transfer by the solar wind was tracked. We used 1-s ACE and Wind magnetometer data during the movement of the Wind SC from the magnetosphere to the libration point L1 against the background of the passage of five high-speed streams. We studied the evolution of MHs observed consistently first on the ACE SC, and then, as a result of their transfer by the wind stream, to the Wind SC. Fifteen MHs were selected whose transfer time between satellites deviated from the calculated one by no more than 15%. Of these, 9 MHs are of the linear type, 5 MHs are of rotational type, and one more was observed against the background of the chaotic behavior of the magnetic field components. The evolution of the MHs during their convective transfer was diverse: from the full shape retention to its significant change both towards the deepening of the hole and the steepening of its front, and towards its significant spreading. The possible modulation effect of MHs on wave phenomena in the magnetosphere is discussed.

Pilipenko V.A., Dovbnya B.V., Martinez-Bedenko V.A., Dobrovolsky M.N. Geomagnetic observations at Vostok station of Soviet Antarctic expeditions: Scientific problems and data archive. Vestnik ONZ RAS. 2020. Vol. 12. NZ4003. DOI:10.2205/2020NZ000366.

We have digitized and made available for free access analog magnetic records of the Soviet Antarctic expeditions to Vostok station from 1967 to 1971. Despite the deployment of several observatories and automatic stations in the polar cap in recent years in Antarctica, observations near the geomagnetic pole at Vostok station with a highly sensitive induction magnetometer with a recording frequency of 20 Hz remain unique. These data make it possible to study the nature of specific impulse and wave electrodynamic disturbances in the polar cap and their relationship with dynamic processes in near-Earth space. Examples of signals and emissions in the polar cap, first recorded at Vostok station, are given: quasi-monochromatic Pc1 pulsations, serpentine emission, discrete broadband Pi1B bursts, Pc3-4 pulsations. The proposed database will help increase Russian participation in research on space weather manifestations in Antarctica.