Geomagnetizm i aèronomiâ

Based on observations at the RT-7.5 radio telescope of the Bauman Moscow State Technical University
at a wavelength of 3.2 mm (93 GHz), along with other ground-based and space instruments (Siberian
radioheliograph, Solar Dynamics Observatory (SDO), Metsähovi radio observatory), the origin of millimeter
radiation from a solar flare was investigated for the SOL2022-05-04T08:45 X-ray class M 5.7 flare. An
analysis of the time profiles of radiation in the X-ray and centimeter ranges showed that the millimeter emission
source is not associated with hot (5 × 105–107 K) coronal plasma. This is also evidenced by the estimate
of the sub-THz flux of radiating hot plasma according to the AIA/SDO data, which turned out to be much
less than the observed values. Indications were obtained of the development of thermal instability in flare
ultraviolet loops. The relationship between the millimeter emission of the flare and the heat source in the
solar chromosphere has been substantiated.

In this paper, we study the similarities and differences of Forbush decreases in solar cycles 23 and
24. Groups of events associated with various types of solar sources were analyzed: coronal mass ejections from
active regions accompanied by solar flares (CME1 group), filament ejections outside active regions (CME2
group), and high-velocity streams from coronal holes (CH group). The distributions and relations of various
parameters were studied: the amplitude of Forbush decreases, the maximum values of the hourly decrease in
the cosmic ray density, the equatorial cosmic ray anisotropy, the solar wind velocity, and the magnetic field
strength, as well as the values of the solar wind velocity and the magnetic field strength 1 hour before the onset
of the Forbush decrease during the event. The results showed that the number of events, parameter values,
and their relations depend on the phase and cycle of solar activity. In the 24th cycle, the number of events in
the CME1 group decreased, did not change in CME2, and increased in CH. The values of the parameters
and the difference between them in various groups of events are higher in cycle 23, which is characterized by
greater asymmetry and long “tails” of distributions. The magnitude of the Forbush decreases in the CME1
group in cycle 23 depends more strongly on the solar wind velocity while, in cycle 24, on the magnetic field
strength, as in the CME2 group in both solar cycles. Multiple linear regression describes the dependences of
the parameters of Forbush reductions in the CME1 and CME2 groups in the 23rd cycle and in the CME1
group in the 24th cycle well.

A new mathematical model was proposed using an ordinary differential equation that analytically
(when the index of geomagnetic activity Kp = const or Kp ≈ const) or numerically (if Kp(t) ≠ const) describes
perpendicular (for a pitch angle of 90°) differential or integral fluxes of relativistic electrons in a geostationary
(geosynchronous) orbit, as well as in any circular orbit in the Earth’s magnetosphere. The model assumes that
the fluxes depend on the local time LT in orbit, the Kp, MacIlvwaine parameter and L, and the perpendicular
differential flux or integral flux of relativistic electrons taken at 0000:00 LT. We use observations of relativistic
(>2 MeV) electron fluxes averaged over the local time hour along the orbit of the GOES spacecraft from 1995
to 2009. The model is compared with these data. Almost perfect agreement was obtained for observations
with the model, where the prediction efficiency of predicting the accuracy of the model at PE = 0.9989. Using
similar data from the GOES 10 allows one to obtain PE = 0.9924. The proposed formulas make it possible to
find, for example, the average value of the perpendicular integral flux of relativistic electrons per day and to
predict the maximum perpendicular integral flux of relativistic electrons in the geostationary orbit approximately
1 day ahead. The nonlinear effect is theoretically predicted in the form of a nonlinear dependence of
the ratio of the maximum perpendicular integral flux to the minimum flux of charged particles in the geostationary
orbit from the Kp-index of geomagnetic activity. Thus far, comparison of the model has been made
with the averaged integral relativistic electron flows fluxes produced for the 0 ≤ Kp < 6 range with a predicted
maximum flow flux ratio of 24.4139 times at Kp = 8 and with the prediction efficiency of predicting the accuracy
of the nonlinear effect PE = 0.8678.

The properties of the variability of the maximum density of the F2-layer Nm at different levels of
solar and geomagnetic activity have been analyzed based on hourly data of the Almaty station (43.2° N, 104° E)
for 1958–1988. The standard deviation σ(x) of the fluctuations of Nm relative to the quiet level
(x = (Nm/Nm0 – 1) × 100, %) and the average shift of these fluctuations xave are used to characterize this
variability. In this path, an empirical model of the F2-layer maximum density Nm0 for low geomagnetic activity
has been created. It has been found that the variability of Nm depends weakly on the level of solar activity.
The dependence of the variability of Nm on geomagnetic activity is one of the main ones, along with the
dependences of this variability on time of day and season. In general, the variance σ2(x) is smaller for quiet
conditions than for periods of high geomagnetic activity. However, during periods of high geomagnetic activity,
a further increase in geomagnetic activity does not lead to an increase in the variance σ2(x). The saturation
in the increase in the variance σ2(x) against the background of a continuing increase in geomagnetic activity
and the absence of this saturation for the average shift xave seems to be a stable property of the variability of
the mid-latitude ionosphere during periods of geomagnetic storms. This conclusion is based on an additional
analysis of ionospheric variability according to data from the Irkutsk and Yamagawa stations, which are
located about 10 degrees north and south of Almaty station, respectively.

The results of ground-based microwave observations of ozone in the middle atmosphere in Apatity
(67° N, 33° E) during three winters (2017–2018, 2018–2019 and 2019–2020) are presented. Long-term ozone
observations were carried out during the period of minimum solar activity for cycles 24 and 25. A mobile
microwave spectrometer with an operating frequency of 110.8 GHz was used in the measurements, which
allows tracking the behavior of ozone in the middle atmosphere with a 15-minute time resolution. The microwave
ozone data from ground-based measurements are compared with the MLS/Aura onboard data. Ground
and airborne data are compared with the data of contact measurements with ozonesondes at Sodankyla st.
(67° N, 27° E). In addition, MLS/Aura data from mid-atmospheric temperature soundings are used to interpret
perturbations in the ozone layer associated with sudden stratospheric warmings. A significant influence
sudden stratospheric warming on the ozone vertical distribution at altitudes of 22–60 km was found. At the
same time, the scale of mesospheric ozone variability (60 km) over Apatity is comparable or exceeds the
known model calculations for assessing the impact of solar proton events and auroral electron precipitation
on the ozone of the polar regions.

We present the results of studying the depths to lithospheric magnetic sources under the Baltic
Shield and adjacent territories of the Russian Plate and the Scandinavian Caledonides. The depths have been
calculated from the global model of the lithospheric geomagnetic field EMAG2v3 by the centroid method.
The minimum depths of the lower boundary of the lithospheric magnetically active layer (30–35 km) were
obtained under the frame of the Baltic Shield, that is, the Russian Plate, the northern and southern parts of
the Scandinavian Caledonides, the maximum (>45 km), under the Scandinavian Peninsula, in the west of
the Svecofennian orogen and the Norrbotten craton. The rest of the territory of the Baltic Shield is characterized
by intermediate depths (38–45 km). Based on a comparison of our estimates of the depth of the lower
boundary of lithospheric magnetic sources with the currently available models of the distribution of the Moho
depth under the study area, it can be seen that for most of the Baltic Shield, the magnetically active layer of the
lithosphere is located within the crust, with the exception of two areas under the Svecofennian orogen and the
eastern part of the Kola Peninsula. This fact supports the hypothesis that the upper mantle has magnetic properties
in regions where positive long-wave anomalies of the geomagnetic field are observed at satellite altitudes.
The obtained results show that the western and eastern parts of the Kola Peninsula can differ not only in the
velocity structure of the crust and upper mantle, which has been previously established by various seismological
methods, but also in the magnetic properties of the upper mantle layer located directly under the crust.