Vol 59, No 6 (2019)

Based on the OMNI2 archival data for 1995–2017, the dynamics of geomagnetic activity indices (Dst, ap, AE, and PC) and interplanetary parameters over the periods of magnetic storms with a minimum of Dst_min ≤ –50 nT induced by different interplanetary sources is analyzed: CIR regions of the interaction of solar wind (SW) streams with different speeds; Sheath-compression regions before interplanetary CMEs (ICMEs); magnetic clouds (MCs) and Ejectas. 181 storms with a monotonic course of the Dst index during the main phases were selected. Similarly to earlier works (Yermolaev et al., 2010a, 2011), which analyzed the OMNI data for 1976–2000, double superposed epoch analysis method with two reference times was used: at the beginning of the main phase and at the minimum Dst_min. This approach allows one to reveal trends in the dynamics of the magnetic activity indices and the SW parameters during storms with different durations of main phases, as well as the difference between these trends for the storms generated by different sources. It is shown that the largest average Dst, aр, AE, and PC indices take place during Sheath storms, and the smallest are registered during the Ejecta storms. The dynamics of the AE and ap indices is similar, and the polar cap index PC dynamics considerably varies during storms with different interplanetary sources, which is evidence of differences between the responses of the polar magnetosphere during storms generated by different sources. There are significant differences between the variations of SW parameters of different storm groups: a very high level of fluctuations of the B and Bz of the IMF is characteristic of the Sheath storms, while, it is close to average for the CIR storms and is considerably lower than average for MCs and Ejecta.

The features of daytime high latitude geomagnetic disturbances and geomagnetic pulsations during the recent strong magnetic storm on August 25–26, 2018, which occurred at the end of the decline phase of the 24th solar activity cycle with a very low level of solar flare activity, are considered. As a rule, during this phase of the solar activity cycle, magnetic storms are caused by high-speed solar wind flows from coronal holes; however, the magnetic storms during the decay of the 24th cycle were caused by coronal mass ejections (CMEs). It was shown that, despite very weak disturbances on the Sun and a low solar wind speed, a rather strong magnetic storm occurred in the Earth’s magnetosphere in August 2018 (Dst = –171 nT). The storm SC with a slight (~25 nT) jump in the Dst index caused quite intense daytime geomagnetic pulsations ipcl at the latitudes of the possible position of the daytime polar cusp. A feature of the recovery phase of this storm was the development of a magnetosphere substorm on a global scale, i.e., the appearance of a negative magnetic bay recorded simultaneously in the auroral night sector and in the polar latitudes of the day sector. A possible interpretation is considered.

The climatological features and behavior of the parameters B0_Neh_I, B1_Neh_I found from N(h) profiles calculated by the curves from the virtual heights during disturbances are studied based on data from the Norilsk station for 2003–2012. There is a greater similarity with the behavior in other latitudinal zones in that the values of B0_Neh_I are higher in summer than in winter and in years of active sun. The B1_Neh_I values are minimal in summer and maximal in winter; the scatter is from 1.3 to 3. Comparison with the IRI-2016 model showed relative deviations of the model values of B0_IRI_A from B0_Neh_I for B0_Neh_I by up to 100% in winter and 10–40% in summer. The winter values were 15–40% and the summer values were 8–50% for the parameter B1_Neh_I. Unlike other zones, the correlation coefficients between B0_Neh_I and the height of the hmF2 maximum, as well as those between B0_Neh_I and the equivalent slab thickness of the ionosphere τ, are lower. There are several types of reaction by the parameters TEC, foF2, B0_Neh_I, and B1_Neh_I to disturbances that, as a first approximation, can be represented as a table of five groups. In most cases, B0_Neh_I increases during disturbances, and B1_Neh_I decreases. The results were not found to depend on the disturbance level. There are large data gaps during disturbances. The total electron content (TEC) of the ionosphere is used to determine the sign of a disturbance.

Empirical median models of the ionosphere are widely used to predict the propagation of high-frequency radio waves. Their adaptation to the real state of the ionosphere is necessary to reduce errors in the flux forecast. A method is proposed for the correction of the IRI-2016 ionosphere model based on data from a ground-based ionosonde network. It does not use the ionospheric parameters themselves but rather their deviations from model values, since these deviations are smoother functions of time and geographical coordinates. The results of numerical modeling according to the proposed correction scheme resulted in a significant improvement in the correspondence of the parameters of radio-wave propagation (the maximum applicable frequency of the path, range, etc.) and real experimental data.

A technique is proposed for the determination of the height profiles of the electron plasma frequency from measurements of the virtual heights during vertical sounding of the ionosphere. Additional information on the height course of the electron concentration from IRI-2016 model data in regions invisible to an ionosonde was used to solve this problem. The proposed algorithms for the correction of height IRI distributions for night- and daytime ionograms, including those with the screening sporadic layer Es, allow solutions that best fit the experimental values of the virtual heights. In the daytime conditions, an IRI profile corrected to the virtual heights in the E region satisfactorily estimates the radio-wave absorption in the D and E regions, and the profile is in good agreement with rocket measurements. The introduction of key parameters into the IRI model (maximal heights and critical frequencies of the layers and parameters B0 and B1, which determine the shape of the profile calculated for the F region) makes it possible to retrieve an IRI profile corrected for real conditions. Analysis of the virtual heights calculated with this profile shows that they significantly differ from the experimental values in the lower F region, which can result in errors in the calculation of the length of the radio path. In addition, difference of profiles in the D and E regions can result in large errors in the absorption of the radio waves reflecting above these regions.

The ionospheric disturbances detected during large earthquake over the region of Haiti on January 12, 2010 on the base the analysis of data GPS-observations are considered in this paper. A complex regional analysis of data from ground stations aggregated in global (IGS and UNAVCO) networks is carried out. Data from 67 ground stations for the period of January 1–15, 2010 was used. More than 7.5 thousand hours of observations were processed. Certain sources of seismic events that are considered possible sources of the revealed inhomogeneous wave structures of the ionosphere are localized. It is found that the selected cases response at ionospheric heights should be opened as a superposition of different processes along with that the ionospheric plasma may be additionally turbulized by a cycle of weaker earthquakes over seismically active regions. Due to the above statements, as well as aftershocks in the monitoring region, the analysis of the wave spectrum slope of ionospheric irregularities shows the availability of a local extreme 5 to 6 h on January 13, 2010. The seismic events evolved in quiet geomagnetic conditions, which made it possible to study ionospheric manifestations of the atmosphere–lithosphere relationships during the examined period.

The results of the determination of the depths to the centroid, the top and bottom boundaries of the magnetoactive layer along the meridional profile starting on the Siberian Platform (60° N, 113° E) and ending in Transbaikalia (50° N, 113° E) are presented. The calculations are performed based on analysis of azimuthally averaged Fourier power spectra of the lithospheric geomagnetic field assigned by the global WDMAM 2.0 model. The obtained estimates show that the depth to the top boundary of the magnetoactive layer along the selected profile is ~2.0 km, but the depths to the centroid and the bottom boundary decrease in the southern direction from 16.6 and 37.4 km to 13.6 and 25.0 km, respectively. Comparison of the parameters of the magnetoactive layer to the structure of the lithosphere in the study region and the distribution of depths of earthquake hypocenters makes it possible to determine that the magnetoactive layer approximately coincides with the seismoactive layer for the North Muya region of the Baikal rift. The magnetoactive layer along the entire profile is located within the Earth’s crust; its thickness is directly proportional to the lithospheric thickness and is inversely proportional to the temperature of the upper mantle. The results are consistent with hypotheses of passive formation of the Baikal rift and are interesting for further geological-geophysical studies in this region, in particular, to determine heat flow and to construct substantiated models of lithospheric evolution.