Geomagnetism and Aeronomy最新文献

An analysis of the dependence of the F2-layer critical frequency on solar activity indices that has been started earlier based on the Juliusruh station data is continued. The data of six stations in the Northern Hemisphere and five stations in the Southern Hemisphere are analyzed in this paper. The determination coefficient R² for the foF2 dependence on solar activity in each particular situation (station, month, local time) is taken as a measure of the quality of that dependence. The conclusion that a well-pronounced diurnal variation in R² is observed in the winter months is confirmed for four solar activity proxies: this value is maximum and changes weakly in the daytime but decreases substantially to the nighttime hours. It is found that the F30 proxy is the best solar proxy to describe the foF2 behavior in the solar cycle, whereas the sunspot number Rz is the worst. Based on a comparison of the changes in R² with LT in the same months at stations of the Northern and Southern hemispheres, it is shown that the aforementioned well-pronounced diurnal behavior in R² is observed only in winter and is absent in summer.

An anomaly in the behavior of galactic cosmic rays in September 2014–February 2015 was studied, which manifested itself as significant modulation of their flux with a period close to the Sun’s rotation. The state of the solar magnetic field and changes in the parameters of the solar wind and interplanetary magnetic field during the specified period are analyzed. The reasons for the longitudinal asymmetry in the distribution of galactic cosmic rays in the inner heliosphere are discussed. It has been established that the studied period is divided into two parts with different physical conditions on the Sun. Conclusions are drawn on the decisive joint influence of sporadic and recurrent events: repeatedly renewed “magnetic traps” created by successive coronal mass ejections from the same longitudinal zone, and anomalously expanded polar coronal holes with an enhanced magnetic field.

The sequence for overcoming the threshold values of a number of physical characteristics for proton event forecasting in real time is discussed. Each characteristic adds a new physical meaning that refines the forecast. To take into account all the characteristics, the following continuous patrol observations are necessary: (1) the magnetic field of the active region (ascent of the flux) and the total magnetic field of the Sun, which can predict the onset of flare activity several days prior to main events; (2) soft X-ray radiation in two channels to calculate the temperature (T) and emission measure of plasma, which can show preheating to T > 10 MK required to begin proton acceleration (the first few minutes before the start of hard X-ray (HXR) radiation with energies >100 keV); (3) HXR radiation >100 keV or microwave radiation (>3 GHz), which indicates the intensity and duration of operation of the electron accelerator (a few to tens of minutes before the arrival of protons with energies >100 MeV); (4) radio emission at plasma frequencies (<1000 MHz), showing the development of the flare process upward into the corona and leading to a coronal mass ejection (CME) several minutes before the onset of type II and IV radio bursts (the first tens of minutes before the appearance of a CME in the field of view of the coronagraph); (5) the direction and velocity of CME propagation, which determine the conditions to release accelerated protons into the heliosphere. These stages of solar proton flares are illustrated by observations of proton events on August 2–9, 2011. To quantitatively predict the onset time, maximum and magnitude of the proton flux, as well as its fluence, it is necessary to create statistical regression models based on all of the listed characteristics of past solar proton events.

One of the most significant features of solar activity is its variability in a wide range of periods with the dominance of the 11-year cycle or the Schwabe cycle. In this article, a wavelet analysis of solar activity data for 1000–1700 obtained using the number of auroras taking into account the contribution of the geomagnetic field taken into account is performed. The results show the stable presence of an 11-year cycle throughout 1000–1700. It is found that there is a systematic increase in the Schwabe cycle length in 1000–1350, after which its decrease is observed. At the same time, the length of the solar cycle increases during the Oort (13 years), Wolf (14 years), and Spörer (14–15 years) grand minima. It is established that the correlation between the amplitude and length of the solar cycle was preserved over the entire time interval of 1000–1700, but its sign changed. It is also found that the correlation between the amplitude of the cycle and the length of the previous cycle is stronger than the correlation between the amplitude and the length of the same cycle. This result is similar to what is known previously for instrumental series. However, we show that this pattern persists over a much longer time interval, and it does not depend on the sign of the correlation. The article also provides indications of the existence of solar activity variations in 1000–1550 with a period of 30–40 years.

During magnetospheric substorms in the F region of the ionosphere and up to altitudes of ~1000 km, a polarization jet (PJ) is developed. Measurements of energetic ring current ions on the AMPTE/CCE satellite and driftmeter data on the DMSP satellites evidence that the formation of PJ is associated with the injection of energetic ions (10–100 keV) into the inner magnetosphere during substorms. In the region of PJ development, the characteristics of the ionospheric plasma change: the plasma density decreases, sometimes by an order of magnitude, and at the same time, the plasma temperature increases significantly. In addition, simultaneously with the westward plasma drift, upward plasma drift is usually observed. The upward ion flux from the region of PJ development of ~10⁹ cm^–2 s^–1 is an order of magnitude greater than the average daytime ion flux from the ionosphere to the plasmasphere. Measurements on the MAGION-5 satellite in the plasmasphere on the same L-shells, where the polarization jet is recorded in the ionosphere, show an increase in the cold ion density. The density “humps” observed near the plasmapause are apparently formed due to plasma flows from the ionosphere accompanying the formation of the polarization jet. Thus, the consequences of substorms are observed throughout almost the entire magnetosphere.

Based on a forecast of solar activity parameters and the model developed by the authors for modulation of Galactic cosmic rays, we forecasted cosmic ray variations in the 25th solar activity cycle. The cosmic ray flux forecast is based on correlation with the number of sunspots (single-parameter model) or with a set of solar (mainly magnetic) parameters (multiparameter model). The forecast for the number of sunspots was taken from published data; the forecast for other solar parameters was done in the study. It is shown that variations in cosmic rays over three years of the current 25th cycle, in general, do not contradict the forecasts and indicate that the 25th solar activity cycle is expected to be slightly more active compared to the 24th.

The dependence of the pitch-angle diffusion efficiency of energetic electrons in the Earth’s magnetosphere on the distribution of the whistler wave field along the geomagnetic flux tube is quantitatively studied for parameters corresponding to the location of the Sura and HAARP HF heating facilities. The expansion of the precipitation energy range with the increase of the region of geomagnetic latitudes occupied by the waves is shown. Using the calculated pitch-angle diffusion coefficient for a given spectrum of waves and their distribution along the flux tube, the ratio of the fluxes of precipitating and trapped particles at low altitude is determined. It is shown that at typical wave intensities corresponding to chorus VLF waves and plasmaspheric hiss, the fluxes of precipitating and trapped electrons can be comparable to each other. At the same time, for the wave amplitudes observed as a result of the action of heating facilities, the flux of precipitating electrons is negligible.

Changes in deviations from the background values of the parameters of the sporadic E ionosphere (Es) are studied: the effective (virtual) height h'Es and limiting reflection frequency (foEs). Basically, the analysis was carried based on hourly measurement data from several Japanese ground stations for vertical sounding of the ionosphere in order to identify possible short-term ionospheric earthquake precursors with intermediate (from 60 to 300 km) hypocentral depths. All known events (12 earthquakes, from 1969 to 2022) are considered for which the necessary ionospheric data in the Japan region and magnitudes (M) ranging from 6.5 to 7.6 are available. From coincidence of the maxima in changes in the considered Es characteristics on the same day at pairs of stations separated by hundreds of kilometers, the time of appearance of possible ionospheric earthquake precursors was recorded. According to the ionospheric data available during the preparation period for the studied earthquakes, a tendency has been identified according to which the time the moment of the main influence is anticipated depends on the magnitude of the impending earthquake. Similarities and differences in the responses of the ionosphere to the preparation of surface (crustal) earthquakes and earthquakes with an intermediate hypocentral depth are revealed. Another tendency is also revealed: earlier appearance of the identified earthquake precursors with increasing hypocentral depth for earthquakes with an intermediate hypocentral depth at the same distances from the epicenter to the observation point.

The article presents the results of a statistical analysis of the distribution of the eddy diffusion coefficient depending on the coordinates in the plasma sheet of Earth’s magnetosphere based on data from the Magnetospheric Multiscale Mission satellite system (MMS) for the period from 2017 to 2022. The localization of satellites inside the plasma sheet was recorded from the concentration and temperature of plasma ions according to the data of the same instruments and the value of plasma parameter β. Significant anisotropy of the eddy diffusion coefficient was revealed. The dependence of the eddy diffusion coefficient on the interplanetary magnetic field is analyzed, showing that with the southern orientation of the interplanetary magnetic field, the eddy diffusion coefficients are 1.5–2 times greater than with the northern orientation. It is also shown that under disturbed geomagnetic conditions (SML < –200 nT), the eddy diffusion coefficients are several times greater than under quiet geomagnetic conditions (SML > –50 nT).

A hardware and software complex for estimating the dispersion distortion bandwidth and fading coherence bandwidth in a satellite (transionospheric) radio channel based on the results of GPS-monitoring of the ionosphere are theoretical substantiated and developed. The basis for solving this problem is development of a structural–physical model of the radio channel, which makes it possible to simultaneously take into account the phase dispersion of the wave and diffraction on small-scale inhomogeneities of the ionosphere. Analytical dependences of the dispersion distortion bandwidth and coherence of frequency-selective fading on the mean value and small-scale fluctuations of the total electron content of the ionosphere are obtained. It is shown that under conditions of ionospheric disturbances, the fading coherence bandwidth can be much smaller than the dispersion band. In accordance with the obtained dependences, a structure is developed for building a hardware and software complex for estimating the dispersion and coherence bandwidths of a satellite radio channel based on improvement of the method for GPS monitoring of the total electron content of the ionosphere with small-scale inhomogeneities.