Pleiades Publishing Ltd

The behavior of the vertical structure of the ionospheric F2 layer, including the variations in the heights of the maximum and bottom of the layer, its half-thickness, and electron content at some fixed heights during postmidnight enhancements in the electron density at the F2 layer maximum (NmF2), has been studied based on the data of the ionospheric vertical sounding, conducted in Alma-Ata (76°55′ E, 43°15′ N) in 2005–2006. The analysis of the amplitude and phase relationships between the measured parameters of the layer made it possible to qualitatively complete the existing concepts of the mechanisms by which the discussed effect is maintained. It is shown that the accelerated decrease in the electron density of the layer within a short time interval preceding the beginning of the postmidnight increase in NmF2 is governed not only by recombination processes but also by the plasma redistribution over the increasing thickness of the layer. The regularly observed effect of the delay in the moment of reversal in the motion direction of the layer bottom relative to the corresponding moment for the layer maximum made it possible to conclude that the meridional wind asynchronously reverses its direction from the poleward daytime to the equatorward nighttime in the entire layer: the direction changes later with decreasing height.

Các giá trị của dòng phát sóng radio và X-ray của mặt trời trong ba chu kỳ hoạt động gần đây đã được nghiên cứu nhằm xác định sự tồn tại của các dao động bán định kỳ thông qua việc xây dựng một phổ hợp nhất. Các chu kỳ bán định kỳ mà chúng tôi phát hiện chủ yếu là do sự điều chế của các dòng phát sóng radio và X-ray kéo dài bởi sự quay tự thân của Mặt Trời. Chúng tôi đặc biệt chú ý đến việc nghiên cứu biến đổi theo thời gian của các chu kỳ bán định kỳ trong các chu kỳ mặt trời thông qua việc xây dựng một ước lượng mẫu về mật độ phổ chuẩn hóa của dữ liệu trong một cửa sổ thời gian chuyển động lên tới 2 năm. Các biểu đồ động về sự biến đổi của các chu kỳ bán định kỳ được xây dựng theo cách này cho thấy rằng sự quay khác biệt của vành đai mặt trời thể hiện ở từng giai đoạn phát triển và tồn tại của ba chu kỳ hoạt động mặt trời gần đây.

The problem of numerical calculation of the spatial dependence of a whistler-radiation beam incident on the nighttime ionosphere from above is considered. For the calculations, we used the collocation method to solve the boundary value problem, the matrix algorithm for the approximate solution of wave equations in a smoothly inhomogeneous plane-layered plasma, and the method of fast Fourier transform in horizontal coordinates. The features of the spatial distribution of the wave field are analyzed for various characteristics of the incident radiation. The fractions of the radiation energy reflected from the upper boundary of the ionosphere that reaches the Earth’s surface are calculated. The wave electric field at an altitude of 400 km, the spatial distribution of the transverse magnetic field, and the polarization of radiation near the Earth’s surface are compared. The results are important for the comparison of the properties of ELF/VLF emissions observed on satellites and on the Earth.

The ordinary mode of gyrosynchrotron radiation was identified to be predominant in some segments of flare loops in solar flares of July 19, 2012, and October 22, 2014. These events were studied by investigation of the quasi-transverse propagation effect on the observed polarization. The analysis involved reconstruction of the magnetic field topology at the linear force-free approximation based on the data of the SDO HMI space telescope and the subsequent simulation of radio emission of flare loops with the GX Simulator software package. The quasi-transverse propagation effect was established to be characteristic for both events, but its influence on the radio emission polarization at a frequency of 17 GHz was observed only in the October 22, 2014 flare.

Solar flare prediction remains an important practical task of space weather. An increase in the amount and quality of observational data and the development of machine-learning methods has led to an improvement in prediction techniques. Additional information has been retrieved from the vector magnetograms; these have been recently supplemented by traditional line-of-sight (LOS) magnetograms. In this work, the problem of the comparative prognostic efficiency of features obtained on the basis of vector data and LOS magnetograms is discussed. Invariants obtained from a topological analysis of LOS magnetograms are used as complexity characteristics of magnetic patterns. Alternatively, the so-called SHARP parameters were used; they were calculated by the data analysis group of the Stanford University Laboratory on the basis of HMI/SDO vector magnetograms and are available online at the website (http://jsoc.stanford.edu/) with the solar dynamics observatory (SDO) database for the entire history of SDO observations. It has been found that the efficiency of large-flare prediction based on topological descriptors of LOS magnetograms in epignosis mode is at least s no worse than the results of prognostic schemes based on vector features. The advantages of the use of topological invariants based on LOS data are discussed.

The interaction between the Alfvén wave and turbulent sheet (TS) with an anomalous conductivity has been considered. High frequency turbulence causes the appearance of not only anomalous field-aligned plasma conductivity but also cross-field conductivity. Alfvén waves can be partially reflect from TS, be absorbed in this sheet, and pass through TS. When field-aligned conductivity is predominant, the relative effectiveness of these processes strongly depends on a cross-field wave scale. If TS is thin as compared to the Alfvén wavelength, the resistive Alfvén wave (λ A ) characterized by the field-aligned resistivity and Alfvén velocity above the sheet is the characteristic parameter responsible for the wave-sheet coupling. A comparison of the loss, estimated using the analytical relationships for a thin sheet and numerically calculated based on the complete formulas for a sheet with a finite thickness, indicates that the approximation of a thin sheet results in reasonable estimates at all wave scales except very small ones. The developed model has been applied to the interpretation of the results of the works on Pi2 pulsation damping during the substorm expansion phase, which indicated that the damping decrement increases at large substorm amplitudes. The estimates indicate that this increase in damping is related to the appearance of anomalous resistivity in the case when field-aligned currents exceed the threshold values necessary for excitation of high frequency turbulence.

The magnetospheric storm on November 20, 2003 was one of two greatest events in 1957–2003. The D st * index reached −472 nT, the polar cap potential drop exceeded 200 kV, the polar cap boundary expanded up to Φ = 60°, the plasma layer density in the synchronous orbit reached 5 cm−3, and the inner edge of the plasma sheet penetrated up to L ∼ 1.5R E. The sequence of disturbance modes including some previously unknown is described. The distribution of the total power input into the magnetosphere between the ionosphere (power Q i) and the ring current (Q DR), as well as the relative roles of the spontaneous substorms and the driven disturbances in the creation of the DR current, is analyzed. The values of the parameter α = Q DR/Q i are calculated with a step of 5 min. It is shown that intervals with α ≪ 1 and with maximums α ≫ 1 were observed in the events under consideration. These results contradict the dominant opinion that the energy input into the magnetosphere during disturbances is primarily dissipated in the ionosphere. The two types of α maximums are observed: one in the mode of a prevailing spontaneous substorm and the other in the mixed mode of the substorm and driven disturbance. It is concluded that both types of the maximums and corresponding enhancements of the DR current appeared due to the plasma turbulization processes in the substorm current wedge. The parameter α appears to slowly increase from α ≪ 1 to α > 1 with increasing activity level; this trend supports the driven model of creating the DR current due to an increase in the electric field of the solar wind.

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.