K. G. Ratovsky

Influence of geomagnetic storms of September 26–30, 2011, on the ionosphere and HF radiowave propagation. I. Ionospheric effects

Geomagnetic storm ionospheric effects observed at different latitudes and longitudes on September 26 and 28–30, 2011, are interpreted with the GSM TIP model. It has been justified that the results of this model can subsequently be used to calculate the HF radiowave ray tracing under quiet conditions and for the selected dates in September 2011. The model calculations are compared with observations of the ionospheric parameters performed by different radiophysical methods. The presented results confirm the classical mechanisms by which positive and negative ionospheric storms are formed during the main phase of a geomagnetic storm. At high latitudes, the electron density is mainly disturbed due to changes in the neutral composition of the thermosphere, resulting in an increase in the chemical loss rates, and the electromagnetic drift, which results in a substantial reconstruction of the high-latitude ionosphere owing to the horizontal plasma transfer. During the storm recovery phase at midlatitudes, electron density positive disturbances are formed in the daytime due to an increase in the n(O)/n(N2) ratio; at the same time, negative effects in the electron density are formed at night as a result of plasma tube devastation. Comparison with the observations indicates that the presented model calculation results can be used to describe a medium for solving problems of radiowave propagation in the ionosphere during the storm main phase on September 26 and during the recovery phase on September 28–30, 2011.

Ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005

This study presents the ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005. The behavior of different ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill and Arecibo stations during the considered period have been numerically calculated, using a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) developed at WD IZMI-RAN. The model calculations of disturbances of the ionospheric parameters during storms qualitatively agree with the experimental data at these midlatitude stations. We suggest that the causes of the quantitative differences between the model calculations and the observational data were the use of the 3-hour Kp index of geomagnetic activity and the dipole approximation of geomagnetic field in GSM TIP, with additional contributions from the effects of solar flares which are not considered in GSM TIP.

Method for studying the spatial-temporal structure of wave-like disturbances in the ionosphere

The method for studying the spatial-temporal structure and propagation characteristics of traveling ionospheric disturbances, using the spectral and cross-correlation analysis of electron density disturbances at different altitudes, obtained with the incoherent scatter radar and vertical sounding ionosonde, is considered. Different algorithms for detecting traveling ionospheric disturbances and calculating the total vector of the disturbance propagation velocity are presented. The results of the method application have been considered in detail, using September 11, 2005, as an example.

Large-scale disturbances of auroral origin during strong magnetic storms of October 29–31, 2003, and November 7–11, 2004, according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered according to measurements of the total electron content (TEC) during the magnetic storms of October 29–31, 2003, and November 7–11, 2004, has been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region (foF2) were used for this purpose. The variations in TEC and foF2 were similar for all events mentioned above. The previous assumption that the region of thickness 150–200 km in the vicinity of the ionospheric F region mainly contributes to TEC modulation was confirmed for the cases when the electron density disturbance at an F region maximum was not more than 50%. However, this region probably becomes more extensive in vertical when the electron density disturbance in the vicinity of the ionospheric F region is about 85%.

Studying atmospheric and ionospheric variabilities from long‐term spectrometric and radio sounding measurements

We investigated the variability in the neutral upper atmosphere and ionosphere parameters over East Siberia. The analysis is based on 2008–2014 data set of mesopause temperature (Tm) obtained from spectrometric measurements of the OH emission (834.0 nm, band (6–2)) at the Institute of Solar-Terrestrial Physics Geophysical Observatory (51.8°N, 103.1°E), and the data of F2 peak electron density (NmF2) from Irkutsk DPS-4 Digisonde (52.3°N, 104.3°E). The seasonal patterns of the NmF2 and Tm variability in different period ranges were analyzed and compared. The period range included day-to-day (periods T > 24 h) and tidal (8 h ≤ T ≤ 24 h) variations as well as variations in the internal gravity wave period range (T < 8 h). The comparison revealed both common features and distinctions in the seasonal patterns of the ionospheric and atmospheric variabilities. The main common feature is that the winter variability exceeds the summer one. In both atmospheric and ionospheric day-to-day variability seasonal variations, there are maxima in winter months and an additional maximum around the autumn equinox. The main distinction is that the equinox peaks observed in the seasonal variations of the diurnal atmospheric variability are not seen in the ionospheric seasonal pattern. The physical reasons of the obtained features are discussed. The revealed similarities in the seasonal behaviors may indicate that planetary waves propagating from the lower atmosphere layers have a significant impact on the mesopause temperature regime and ionospheric day-to-day variations.

Studies of dynamic characteristics of atmospheric planetary waves during stratospheric warmings 2006–2013

Shown that the temperature disturbances, propagated during stratospheric warmings, are result of interference of at least two waves. Two-wave interference model of stratospheric warming was developed. Characteristics of planetary waves, for warmings 2006-2013 were obtained by using this model. Periods of disturbances vary from 5 to 45 days. Vertical wave numbers range is 20-150 km. Amplitudes and horizontal wave numbers obtained by the two-wave models, vary smoothly in space and time, forming vorticity-like structure. On the basis of regular, continuous observations from the Irkutsk ionosonde DSP-4, was shown that number of traveling ionospheric disturbances tend to increase during stratospheric warmings. Comparing of planetary waves characteristics for warmings 2006-2013 was done.

Relation of internal gravity wave anisotropy with neutral wind characteristics in the upper atmosphere

This paper studies the interaction of internal gravity waves (IGW) with neutral wind using the statistics of traveling ionospheric disturbances (TID) from the Radio Physical Complex of the Institute of Solar-Terrestrial Physics. The complex includes the Irkutsk Incoherent Scatter Radar (IISR), Irkutsk Ionosonde (DPS-4), and Ekaterinburg HF Radar (EKB). The aim of this study is to give a common explanation for the TID azimuth distributions obtained with the IISR-ionosonde and HF coherent radar and show that the measurements of 3-D TID characteristics put into the hands of researchers an important tool to study neutral wind in the thermosphere. The distinctive features of this study are the following: (1) using different TID statistics from independent tools and, correspondingly, independent methods for determining TID characteristics; (2) using the 3-D TID characteristics for testing the wind-filtering hypothesis, which allows us to separate the IGW induced TIDs from TIDs of other nature and identify three TID types depending on their elevation angles; (3) using the local time - azimuth distribution of the TID number for testing the wind-filtering hypothesis. This study allowed us to conclude that the observed IGW azimuth anisotropy can be mainly explained by the wind filtration mechanism with considering winds at 90-250 km heights. Using the 3-D IGW characteristics allow us estimating neutral wind parameters. Proposed methods are applicable for any tools which can obtain TID 3-D characteristics. Using the proposed methods will enable to organize a worldwide campaign to improve the existing neutral wind models.

Comparative analysis of atmospheric and ionospheric variability by measurements of temperature in the mesopause region and peak electron density NmF2

The results of studying the atmospheric and ionospheric variability in the region of Eastern Siberia are presented. The analysis involved data on the atmosphere temperature at mesopause heights (Tm) and vertical sounding data on the peak electron density (NmF2). The data on temperature were obtained by spectrometric observations of the hydroxyl molecule emission (band ОН (6-2), 834.0 nm, maximum emission height ~87 km). The analysis covers the period from 2008 to 2015. Seasonal and year-to-year variations in the variability of Tm and NmF2 were studied and compared in different time periods: day-to-day variations (T > 24 h), tidal variations (8 h ≤ T ≤ 24 h), and variations with periods of internal gravity waves (T < 8 h). Both common features and distinctions in the behavior of the analyzed parameters have been found, and their possible physical causes are analyzed.

The project of monitoring the ionosphere over Russian Federation by means of digital FMCW ionosondes network

For monitoring the current ionospheric conditions over Russian Federation area in quasi real-time we offer to use modern digital FMCW vertical incidence ionospheric stations capable to receive oblique incidence signals during vertical sounding session. For determination of ionospheric stations locations (Fig. 1) the spatial correlation criterion was used, which is measure how much deviations from regular variation (defined by model or median) at one point of space are differed from other. Measure function of spatial correlation is radius of spatial correlation which determined as range where spatial correlation function goes down to 0.7. Newness of such ionospheric network consists in combining capabilities of vertical incidence and oblique incidence ionosondes. It becomes possible because of operative technique for reconstruction ionospheric parameters at path midpoint and appearance of modern digital multichannel receivers which were examined by few continuous experimental works in Russian Federation.

Vertical ionosphere sounding using continuous signals with linear frequency modulation

Consideration of the digital chirp sounder design for the modern systems of a geophysical monitoring, communication channels state forecasting and the research problems solution is given. Given the comparative results of pulsed and of continuous signal vertical sounding ionosondes.