Geomagnetism and Aeronomy最新文献

The ionosphere is an inhomogeneous and anisotropic medium in nature. It causes degradation in the performance of positioning through Global Navigation Satellite Systems (GNSS). Generally, the vertical total electron content (VTEC) is used to characterize the ionosphere. The present study can further be used to enhance positional accuracy with a Navigation with Indian Constellation (NavIC) dual-frequency receiver, especially in the Northern region of India where the elevation angle is consistently very low. At such low elevation angles, converting Slant Total Electron Content (STEC) to VTEC and vice versa introduces errors. Therefore, in this study, STEC is used directly instead of VTEC. STEC can be used to analyze dynamic variations in the ionosphere and investigate local and regional ionospheric disturbances. The STEC is dependent on various factors such as solar activity, elevation and azimuth angle of the satellite, seasonal variation etc. Therefore, it is necessary to evaluate the dynamic attributes and variability of STEC to maintain high accuracy in any ionospheric conditions. This research paper focuses on the evaluation of dynamic attributes and variability of Ionospheric Slant Total Electron Content using Navigation with Indian Constellation (NavIC) satellite system. This study utilizes 19 months (from June 2017 to December 2018) dual frequency NavIC data to compute and analyze STEC. The results show a significant effect of satellite elevation angle, azimuth angle, and seasonal STEC variability. The discussion highlights the suitability of NavIC geostationary satellites (PRN3, PRN6, and PRN7) of NavIC for ionospheric studies, space weather applications, and identification of local ionospheric irregularities. The research findings demonstrate the importance of considering dynamic attributes and variability of STEC to model applications for maintaining high accuracy in case of any ionospheric irregularity. Additionally, this research could serve as a reference for future studies in the field of ionospheric-plasmapheric studies and space weather applications using NavIC system.

Autocorrelations of fragments of the Wolf number series (V2) are considered for 6-year forecasting (solar half-cycle). For physical and optimal reasons, fragments similar to one and half cycles are used. Testing is successfully performed on sufficiently reliable pairs of fragments of the series consisting of a fixed and a time-shifted fragment. A pair is selected for testing if the correlation coefficient is 0.91 or more when its components are combined. The original modification of the fixed fragment and the parts of the series following it are used. Similarly, 6-year forecasts after 2023 are produced from 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), and (1985.5–2000.5). The maximum Wolf number (161 ± 30) is expected in mid-2024.

Estimates of the long-term changes in the ionospheric F2 layer parameters (slab thickness, total electron content, height, and maximal electron concentration) are presented and mutually compared. It is shown that these estimates mutually agree and show that both foF2 and hmF2 have been decreasing in recent decades.

The article presents the first results of identifying trends in annual average ionospheric indices ΔIG₁₂ and ΔT₁₂, which are obtained after excluding from IG₁₂ and T₁₂ the dependence of these indices on solar activity indices. In this case, solar activity indices are F10 and F30—solar radio emission fluxes at 10.7 and 30 cm. It was found that for the interval of 1957–2023, all analyzed linear trends are negative, i.e., quantities ΔIG₁₂ and ΔT₁₂ decrease over time, and these trends are significant. In absolute value, they are maximum for ΔIG₁₂, taking into account the IG₁₂ dependence on F10₁₂, and minimum for ΔT₁₂, taking into account the T₁₂ dependence on F30₁₂. Account for the nonlinearity of trends shows that, e.g., after 2010, they intensified. Relations are presented that make it possible, based on data from trends of the ionospheric indices (ΔIG₁₂ or ΔT₁₂), to judge the nature of the Δ foF2 trend over a specific point. For this, using the IRI model for foF2, a coefficient was obtained that gives the relationship between the trends of the ionospheric index and Δ foF2 over this point. Comparison with experimental data at mid-latitudes revealed that trends of the ionospheric indices make it possible to correctly determine the sign of the Δ foF2 trend and the general tendency for this trend change, but the calculated value of the trend over a specific point may differ markedly from the experimental data.

When radon emanates, the conductivity in surface air increases, which causes variation in the electric field not only in the lower atmosphere, but also in the ionosphere. There have been proposals to use such ionospheric disturbances as earthquake precursors. The ionospheric electric fields are calculated using a quasi-stationary model of an atmospheric conductor including the ionosphere. Earlier, we showed that even with extreme radon emanation, electric field disturbances in the E- and F-regions of the ionosphere are several orders of magnitude smaller than the supposed earthquake precursors and smaller than the fields usually existing there, which are created by other generators. In this paper, we focus on the D-region. In the vertical component of the electric field strength, the main contribution to the D-region comes from the fair-weather field. It is shown that in the D-region, the vertical electric field component over the area of intense radon emanation can double in comparison with the fair-weather field. A detailed spatial pattern of disturbances of electric fields and currents in the atmosphere and ionosphere over the radon emanation region is constructed.

Based on a large amount of experimental material, the hourly values of the solar wind speed and proton temperature were compared; the expected proton temperature and temperature index (the ratio of the observed temperature to the expected one) were calculated. Using the Cosmic Ray Variations Database, from 1997 to 2022 low-temperature periods were identified (intervals lasting more 2 h, in which hourly values of the temperature index less than 0.5). The study investigated (a) statistical relationships between the parameters of low-temperature periods and the characteristics of Forbush decreases associated with different types of solar sources; (b) distributions of parameters of low-temperature periods for interplanetary disturbances containing or not containing a magnetic cloud. The results showed that with increasing duration of the low-temperature period, the proportion of events associated with ejections from active regions increases, while the proportion of recurrent events and events associated with ejections outside active regions decreases. The correlation of the parameters of low-temperature periods with the magnitude of Forbush decreases is weak; with the equatorial anisotropy of cosmic rays, moderate; and with the azimuthal anisotropy, significant. The solar wind speed and magnetic field strength correlate moderately with the temperature index, and the correlation of the range of these parameters with the duration of low-temperature periods is significant or strong.

Long-term trends of the three-dimensional Plumb wave activity flux are studied using data from the JRA-55 global atmospheric reanalysis. The vertical component of the Plumb flux characterizes the propagation of atmospheric planetary waves generated in the troposphere to the upper atmosphere and is used for the analysis of the stratosphere–troposphere dynamic interaction. The study of the wave activity flux covers three latitudinal sectors of the Northern Hemisphere from December to March for a 64-year period since 1958. It is shown that in January and March over the Russian Far East there is a statistically significant trend for an increase in the wave activity flux from the troposphere to the stratosphere, which can contribute to an increase in the frequency of cold wave formation in the mid-latitude troposphere. The study of the stratosphere–troposphere dynamic interaction in general and wave activity fluxes in particular is necessary for solving problems related to both global and regional climatic changes and mixing of long-lived atmospheric components.

A method for forecasting geomagnetic storms based on deep learning neural networks using digital time series processing for matrix observations of the URAGAN muon hodoscope and scalar Dst-indices has been developed. A scheme of computational operations and extrapolation formulas for matrix observations are proposed. The a variant of the neural network software module and its parameters are chosen. A decision-making rule is formed to forecast and assess the probabilities of correct and false forecasts of geomagnetic storms. An experimental study of estimates of the probabilistic characteristics and forecasting intervals of geomagnetic storms has confirmed the efficiency of the method. The obtained forecasting results are oriented towards solving a number of solar–terrestrial physics and national economic problems.

The article studies quantitative characteristics of the mechanism of excitation of VLF chorus emissions by analyzing high-resolution data from the Van Allen Probes. A typical example of chorus with spectral forms in the lower frequency band (below half of the electron cyclotron frequency) in the region of the local minimum of the magnetic field behind the plasmapause in the middle magnetosphere is presented. A new method of analysis of quasi-harmonic signals recorded with high digitization frequency is proposed and implemented by the example of chorus in the lower frequency band. The results of wave field measurements in a high-resolution data channel are presented in the form of a rectangular event matrix, each row of which corresponds to one cycle of the wave process. In the event matrix, the rows corresponding to the fragments of the implementation that characterize the natural source of short electromagnetic pulses are selected. This made it possible to determine the complex eigenvalues of the characteristic equation of the source at the linear stage of chorus excitation. The values of the roots of the characteristic equation obtained by analyzing the data of chorus observations correspond to the implementation of chorus excitation by the amplification of noise electromagnetic pulses in a planar densification waveguide.

The influence of the ionospheric wind on internal gravity waves is considered. It is shown that interaction of wind in the ionosphere with the geomagnetic field leads to occurrence of the Ampére force, the vertical gradient of which modifies the properties of internal gravity waves. Such interaction results in the discrete spectrum of ionospheric fluctuations with the main period about 30 min. The increase in the Ampére force due to an electric field of seismic origin leads to the appearance of a maximum with shorter periods of about 10 and 22 min in the spectrum of ionosphere fluctuations. Observations of phase and amplitude fluctuation of a radio wave reflected from the ionosphere during increasing seismic activity are confirmed by the results of the considered model.