Geomagnetizm i aèronomiâ

Autocorrelations of fragments of a series of Wolf numbers (Version 2) are considered for the purpose of forecasting for 6 years (half a solar activity cycle). Fragments similar to one and a half cycles were used for physical and optimal reasons. Testing was successfully carried out on fairly reliable pairs of series fragments, consisting of a fixed and a time-shifted fragment. Pairs were selected for testing if the correlation coefficient of their superposition was 0.91 or more. An original modification of the fixed fragment and the following segments of the series was used. Similarly, forecasts were made for 6 years after 2023, based on the fragment (2008.5−2023.5), which has correlation coefficients from 0.81 to 0.96 with fragments (1978.5−1993.5), (1901.5−1916.5), (1922.5−1937.5), (1964.5−1979.5), (1985.5−2000.5). The maximum value of the Wolf number (161 ± 30) is expected in mid-2024.

The work includes the development of a method for determining the rigidity of geomagnetic cutoff based on tracing charged particles in the Earth’s magnetic field using the particle-in-cell method, implemented in the Buneman–Boris scheme. To test the method, calculations of the geomagnetic cutoff rigidity were carried out in the field of an ideal dipole and in the field specified by the IGRF model. In the first case, the obtained data were compared with analytical values. The calculation accuracy in this case was 3 MV. In the second case, the penumbra pattern was reproduced at different geographical points for different periods, and the stability of the method to small perturbations of the initial parameters was also investigated. As the main results of the work, maps of geomagnetic cutoff rigidity at the altitudes of low-orbit satellites for different directions in space, as well as their variations from 1900 to 2015, were constructed and analyzed.

The results of identifying trends in the annual average ionospheric indices ΔIG and ΔT are presented, which were obtained after excluding from IG and T the dependence of these indices on the annual average solar activity indices. The solar activity indices were F10, Ly-a and MgII – solar radiation fluxes at 10.7 cm, in the Lyman-alpha line of hydrogen (121.567 nm) and the ratio of the central part to the flanks in the magnesium emission band 276-284 nm. Two-time intervals (in years), 1980–2012 and 2013–2023, are considered. It was found that for the interval 1980–2012 all analyzed linear trends were negative, i.e. ΔIG and ΔT values decreased over time. They were very weak and insignificant. Fluctuations of ΔIG and ΔT relative to trends for Ly-a were almost twice as large as for F10 and MgII. In the interval 2013–2023, all analyzed linear trends intensified and became significant, i.e. the rate of decrease in ΔIG and ΔT over time increased. For MgII this rate was almost twice as high as for F10. For the interval 2013–2023, the MgII index overestimated the contribution of solar radiation to ionospheric indices, especially during the growth phase of solar cycle 25, which began at the end of 2019. As a result, in the growth phase of solar cycle 25, the F10 index became a more adequate indicator of solar activity for ionospheric indices than MgII. In the interval 1980–2012, the F10 and MgII indices changed almost synchronously. The growth phase of solar cycle 25 was the first time this synchrony was disrupted for the entire period of MgII measurements.

Attempts have been made repeatedly to investigate the effect of magnetic activity on the equatorial plasma bubble (EPB) generation. At the moment, it is generally accepted that magnetic activity tends to suppress the EPB generation and evolution in the pre-midnight sector. As for the post-midnight sector, it is believed that the EPB occurrence probability will increase after midnight as magnetic activity increases. Moreover, the growth rates of the EPB occurrence probability will strongly depend on solar activity: at the solar activity minimum, they will be the most significant. A sufficient amount of the observations is required to confirm these ideas. For this purpose, the EPB observations obtained on board the ISS-b satellite (~972−1220 km, 1978−1979) in the pre- and post-midnight sectors are best suited. The data were considered in two latitudinal regions: equatorial/low-latitudinal (± 20°) and mid-latitudinal ± (20°−52°) regions. LT- and Kp-variations of the EPB occurrence probability were calculated for both groups. (1) It was revealed that the occurrence probability maximum of the EPBs recorded at the equator and in low latitudes is in the pre-midnight sector. The EPB occurrence probability decreases with increasing Kp index with a delay of 3 and 9 hours before the EPB detection. (2) However, the occurrence probability maximum of the EPBs recorded at the mid-latitudes is in the post-midnight sector. Their occurrence probability increases slightly as Kp index increases, when Kp is a 9-hours delayed one. Thus, the idea of the ionospheric disturbance dynamo (IDD) influence on the post-midnight EPB generation has been confirmed. IDD mechanism sets in after some hours of enhanced geomagnetic activity and favors the generation. However, its influence is weakened during the years of increased solar activity.

Long-term trends of three-dimensional wave activity Plumb’s fluxes are studied using the JRA-55 global reanalysis of the atmosphere. The vertical component of wave activity Plumb’s flux characterizes the propagation of atmospheric planetary waves generated in the troposphere into the upper atmosphere, and is used to analyze the stratosphere-troposphere dynamic interaction. The study of the wave activity flux was conducted for three latitudinal sectors of the Northern Hemisphere for months from December to March, over a 64-year period since 1958. It is shown that a statistically significant trend of wave activity flux from the troposphere to the stratosphere increase is observed over the Russian Far East in January and March. This can contribute to an increase in the frequency of cold waves formation in the middle latitudes troposphere. The study of stratosphere-troposphere dynamic interaction in general and wave activity fluxes in particular is necessary to task solution related to both global and regional climate changes and mixing of long-lived atmospheric components.

A wavelet analysis of the average monthly changes in the values of the time series of the geomagnetic field, as well as a correlation analysis of the wavelet coefficients with fixed values of the scale factor for three European, Asian and North American magnetic observatories, was performed. The results obtained suggest that the processes related to the Jerke phenomenon have a morphologically complex character, dynamics that differ significantly for different time scales and probably represent the consequences of a complex of similar in nature, but different phenomena.

The induction and momentum equations are simplified to a dynamical system for the kinetic and magnetic energies in the Earth’s core. Stable stationary points of this system give a geomagnetic field of ~ 10 mT and the cosecant of the angle between the magnetic field vector and the fluid velocity vector is on average about 500 at a known speed of ~ 1 mm/sec and a generally accepted dynamo power of ~ 1 TW. With a generally known typical geomagnetic time of the order of a thousand years, harmonic secular variations of the order of several decades and rapid exponential changes of the order of several months, possibly associated with jerks, were obtained. All this is in good agreement with dynamo theory, paleomagnetic reconstructions, numerical modeling and observations. Geomagnetic energy ~ 10 mJ/kg is four orders of magnitude greater than kinetic energy. Under conditions of such dominance of magnetic energy, an analytical solution was obtained, which over time converges to stable stationary points. Apparently unlikely catastrophes with virtually zero magnetic energy near partially stable stationary points are discussed.