Vol 56, No 3 (2016)

Long term cosmic ray variations in the heliosphere in cycles 21–24 are described using the multiparametric model, including characteristics of solar activity. Long-term observations of the cosmic ray intensity, global solar magnetic field characteristics, and characteristics taking into account sporadic solar activity are the initial data for modeling cosmic ray variations. Data on intensity have been obtained from observations at the global ground network of neutron monitors and stratospheric sounding. The characteristics of the regions with an open magnetic field (coronal holes) have been introduced into the model in order to improve the description of long-term variations. The location (latitude), area, and magnetic flux of coronal holes have been used as parameters of this solar activity type manifestation. The modulation has been modeled for the entire studied period (1976–2012) and independently for periods with identical global solar magnetic field directions with regard to the cosmic ray variation delay relative to variations in the solar activity characteristics. It has been shown that the accuracy of long-term variation description improves when coronal hole characteristics are taken into account.

As a rule, bright auroral arcs evolve near the poleward boundary of the auroral oval at the growth phase of a substorm, a phenomenon that is known to occur near the poleward edge of the auroral oval. The closeness of these arcs to the projection of the magnetic separatrix on the night side suggests that their generation is related to magnetic reconnection in the magnetospheric tail in a particular way. In this study this suggestion is confirmed by the fact that integral brightness of the auroral oval at the poleward edge correlates with magnetic field structures in the solar wind that are observed by ACE and Wind satellites at distances of 50–300 R_E upstream and are shifted towards the magnetospheric tail with time delays of ~ 10–80 min, consistent with measurements of the solar wind velocity. About 50 examples of this correlation have been found. The possible physical mechanisms of the effect observed are discussed.

The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm (SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm^–3) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations (ipcl and vlp) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.

The problem of how the deep minimum of solar activity of 2008–2009 influenced trends in the critical frequency of the F2 layer and whether the negative trends in foF2 are conserved in the following five years is considered in the paper. The initial data series used in previous publications by the authors are completed by data to 2014 (2015). Methods of searching for trends that were described in the past several times by the authors were applied. It was found that, in the vast majority of cases, the monotonous change in the curves used to derive the foF2 trend was distorted in years close to the anomalously low minimum of solar activity in 2008–2009. That decreased the obtained trend in the critical frequency as compared with the results based on the data to 2009. However, subsequent years again lead to a tendency toward monotonous decrease in foF2. The causes of the anomalies indicated above lie apparently in the inadequacy of the solar activity index F10.7 for the description of changes in the aeronomical parameters determining the foF2 behavior in the period of a very deep minimum of activity that is widely described in some publications.

We present a brief description and comparative analysis of the Klobuchar, GEMTEC, and NTCM-GL models of total electron content in the ionosphere. The quality of model performance against experimental data on the total electron content is compared. Statistical estimates for the residual positioning error are obtained for each of these models on the basis of the international Global Navigation Satellite Systems (GNSS) Service data. The GEMTEC and NTCM-GL models are shown to have a higher positioning accuracy than the Klobuchar model. The best results of the ionospheric error correction are provided by the GEMTEC model.

Based on data from ground-based vertical sounding stations, the behaviors of the ionosphere F region before a strong M 6.8 earthquake off the coast of Hokkaido, Japan, and during the moderate magnetic storm before this earthquake are compared. It was found that the critical frequency of the ionosphere F region (foF2) above the Wakkanai ground-based ionosphere vertical sounding station, which was located in the preparation zone of this earthquake, suffered a long-term disturbance of slightly more than an hour nearly half a day before the earthquake. The magnitude of earthquake-induced disturbance is comparable to that caused by a magnetic storm.

A database of continuous measurements of the VLF pulsed flux of the natural electromagnetic field of the Earth (NEMFE) in southern Siberia during the period from March 31, 2008 to the present was created. Analysis of long-term continuous observations has shown that NEMFE diurnal variations have stable seasonal changes. A high interannual correlation coefficient of NEMFE diurnal variations for the same months in 2008–2014 was discovered. The analysis of data from spaced recorders has shown a high degree of spatial correlation, which indicates a single local mechanism of the NEMFE formation.

Marine magnetic anomalies of the tiny wiggles (TW) type can be used to solve geohistorical and paleomagnetic problems. The model fields corresponding to Paleocene–Eocene anomalies in the northwestern Indian Ocean, which were formed during the fast-spreading stage, were studied. For these fields, widely used interpretation methods were compared with a method proposed previously by the authors. The testing was performed with first the classical block model and then more complex models reflecting actual processes of oceanic accretion and magnetic field variations in the past. It was shown that the proposed method has advantages for this problem; it gives an error close to the minimum possible error and can adequately be used in interpretations. Spectral and statistical methods are used to estimate the magnetic anomaly resolving power and to study some factors that can exert a distorting influence. In addition, model examples have been used to indicate how the TW determination accuracy is affected by diurnal variations in the main magnetic field (MMF) and by ancient magnetization vector determination errors.