Vol 58, No 6 (2018)

The crossings of the magnetopause and low-latitude boundary layer by the THEMIS-B satellite in the spring of 2008 on the dusk flank under large negative X_GSM (from –17R_E to –19R_E) are studied. The parameters of plasma and magnetic field are analyzed from the data of ESA and MGF instruments. The changes in the total pressure, magnetic field pressure, and plasma pressure component during the transition from the magnetosheath to the plasma sheet (PS) are analyzed. The values of plasma pressures under the magnetopause at the edge of the PS for the considered events are determined. The applicability of the obtained results to the determination of the position of the boundary between the tail current and the ring current is discussed.

The magnetosheath is a natural laboratory for the study of plasma turbulence. The magnetopause and the bow shock prevent freely development of turbulence and modify turbulent cascade. In this paper, the effect of the magnetosheath boundaries on the forms of frequency spectra of ion flux fluctuations is analyzed based on statistics. In addition, variance in the spectrum characteristics are considered, such as spectral slope at the magnetohydrodynamic (MHD) and kinetic scales, as well as the frequency of transition between these scales when the satellite crosses the magnetosheath. The analysis is based on measurement of the ion flux by the Fast Solar Wind Monitor (BMSW) onboard the Spektr-R satellite with a time resolution of 31 ms. It is shown that the probability of observing spectra of the particular type greatly varies upon crossing of the magnetosheath: standard spectra with two slopes and a distinct breakpoint are observed in most cases in all parts of the magnetosheath, and the probability of their observation is slightly higher upon the approach to the magnetopause; spectra with a peak in the region of transition between the scales (MHD and kinetic) are more often observed closer to the bow shock, and spectra with a plateau in the region of transition between the scales are usually observed closer to the magnetopause. It is revealed that the spectra at the MHD scales immediately behind the bow shock are described by a power function with index –1.3 on average, which noticeably differs from the index of –5/3 predicted by the classical theories. The spectra at the kinetic scales immediately behind the shock wave become steeper than in the solar wind and slightly flatten on the approach to the magnetopause.

This paper is a continuation of the research conducted by Nikolaeva et al. (2015, 2017), in which the possible difference in the generation of magnetic storms induced by different large-scale types of solar wind (SW) streams (corotating interaction regions (CIRs), sheaths, magnetic clouds (MCs), and ejecta) were discussed. It was shown in these works that sheath- and CIR-induced magnetic storms demonstrate the greatest geoeffectiveness for the period 1976–2000 with the coupling function introduced by Burton et al. (1975), which couples the integral electric field of the SW Ey = VBz to the Dst and Dst* indices. The use of 12 other coupling functions with different interplanetary parameters and magnetosphere states available in the literature has shown that their efficiency for each type of SW streams depends on the type of function used. In this paper, we study the generation efficiency of the main storm phase for the same four stream types (CIR, sheath, MC, and ejecta) based on OMNI data for the period 1995–2016, which contains a more complete set of data on SW parameters. The results confirm that magnetic storm generation depends on the type of interplanetary source and the high efficiency of the coupling function in the form of an integral of Ey for sheath and CIR streams. The problems of the applicability of the coupling functions used to predict magnetic storms are discussed.

According to the cyclicity pattern of a reliable series of the relative sunspot number, cycle 24 opens the second epoch of lowered solar activity (SA). The main specific feature of this epoch (five cycles) is the inhibition of high solar cycles and the strict fulfillment of basic observational rules in the development of individual cycles. The more than two-fold decrease in the background values of the solar general magnetic field by the end of cycle 23 led to a complete rearrangement of physical conditions, both on the Sun and in the inner heliosphere, and affected the state of the near-Earth space (NES). After 9.2 years of development, the current solar cycle, 24, became a cycle of low magnitude (W* = 81.9) with reduced flare activity, lower geoeffectiveness of active solar phenomena, and a near absence of the most powerful flare events, solar proton events, geomagnetic activity manifestations, and ionospheric disturbances.

The relationships between circulation characteristics in the lower atmosphere of the Northern Hemisphere and the sunspot cycle are analyzed with the use of the superposed epoch method and elements of correlation analysis on the basis of data on the length of elementary circulation processes of different types (according to Dzerdzeevsky classification) and the time series of Wolf numbers for 1899–2016. It is ascertained that a general intensification of solar activity promotes an increase in the length of meridional forms of circulation, but its effect on different subtypes of elementary circulation mechanisms is different. Seasonal differences in the solar effect on the lower atmosphere are also revealed.

A comprehensive analysis of the polar substorm registered by IMAGE network stations close to the poleward boundary of the auroral oval has been carried out with THEMIS, CLUSTER, and GEOTAIL satellites in favorable positions for analysis. The observation interval is characterized by a low level of geomagnetic activity. The polar substorm looked like three negative, bay-like disturbances and developed within an ordinary substorm registered at stations in the middle of the auroral zone half an hour before the polar substorm. Each bay-like disturbance of the polar substorm was accompanied by a poleward drift of aurora and westward electrojet, a Pi2 pulsation group, a surge of magnetic activity over the range of 0.1–10 Hz, and enhancement of electronic precipitations over Spitsbergen. The differences between the first activation and two subsequent ones in the aurora dynamics, ionospheric convection, and electronic precipitations are revealed. The disturbed zone longitudinal sizes and position in the magnetosphere are estimated. Possible causes of the substorm onset and disturbances associated with it are discussed. The results of the study expand the statistics on the polar substorm phenomenon and will enable insight into its nature.

The contribution of the solar f_sol and auroral f_avr components of foE to the critical frequency of the E layer foE are estimated based on an analysis of the medians of the E-layer critical frequency foE in the nighttime (2200–0200 LT) auroral region with allowance for the noncoincidence in the heights of maxima of these components. This noncoincidence is taken into account with a correction coefficient that manifests the relation of f_sol to the critical frequency of the E layer due to solar radiation foE_sol. The analytical dependence of this coefficient on the solar zenith angle for χ < 85° is derived. It is shown that one can usually disregard the contribution of f_sol in foE in the nighttime auroral region for χ > 85° and approximately foE = foE_avr for these conditions in which foE_avr is the critical frequency of the E layer due to precipitation of auroral electrons. It is obtained that the allowance for the noncoincidence of the heights of maxima in the solar and auroral components of foE with estimation of the annual changes in foE_avr based on the foE measurements leads to an increase in foE_avr in summer and thus provides a decrease in the amplitude of the winter anomaly in foE_avr. Nevertheless, even in this case, the amplitude of the winter anomaly in foE_avr is higher than the winter anomaly in foE, and that demonstrates the important role of accelerated auroral electrons in formation of this anomaly.