Search

Using previously developed methods for determining the three-dimensional spatial–temporal structure of traveling ionospheric disturbances and the automatic detection of wave disturbances, we analyzed data obtained simultaneously with the Irkutsk Incoherent Scatter Radar and Irkutsk ionosonde. The analysis relies on long continuous series of observations acquired during winter seasons in 2010–2014. We obtained representative statistics of traveling ionospheric disturbances characteristics including the full velocity vector. We analyzed the characteristics of traveling ionospheric disturbances with 1–6 h periods comparing them against the dispersion relations for internal gravity waves in the Boussinesq and Hines approximations. It was shown that, with due consideration for the horizontal neutral wind, most of the observed ionospheric disturbances agrees with the laws of internal gravity waves propagation in the upper atmosphere. It was found that azimuthal anisotropy of internal gravity waves characteristics allows us to obtain the diurnal variations of zonal and meridional neutral winds in the upper atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the spatio-temporal structure of traveling ionospheric disturbances characteristics is studied on the base of the electron density profiles measured by two beams of the Irkutsk incoherent scatter radar and the Irkutsk Digisonde. The technique for determination of spatial–temporal structure of wavelike ionospheric disturbances was developed using cross-correlation and spectrum analysis of electron density. The automated method for extracting ionospheric disturbances including both long-period day-to-day variability and short-period variations has been developed. Full analyses of January 15–February 17, 2011 data, including total velocity vector, was carry out for 1–6h ionospheric disturbances, corresponding to internal gravitational waves. The propagation characteristics agree with those obtained from the known studies of the wavelike ionospheric disturbances. An automated method of ionospheric disturbances analysis was created on the basis of regular continuous measurements with the Irkutsk Digisonde. The statistical analysis of electron density disturbances was carried out for 2004–2009 period. [Copyright &y& Elsevier]

Abstract We study the effects of the middle atmosphere dynamics on the mid-latitude and subauroral ionosphere during the winter jet stream that occurred at the stratosphere/lower mesosphere heights in the Northern Hemisphere over 2008–2013. The used ionospheric data were obtained from measurements taken at the vertical sounding ionosonde chain covering the entire Eurasian continent. We reveal regional features of the F2 -layer ionospheric response to dynamic processes during the winter circumpolar vortex evolution in the strato-mesosphere. The variations in the ionospheric parameters observed at different longitudes in the Northern Hemisphere significantly depended on the ionosonde position relative to the jet stream zone in the strato-mesosphere. The difference in critical frequency values for the ionosondes spaced longitudinally by only 15–20° could reach about 1.5–2 MHz, depending on the observation point location under the jet stream or off the latter. We consider the molecular gas upwelling/downwelling to/from the lower thermosphere in active regions of circulation as a mechanism for the underlying atmosphere impact on the ionosphere. Irregular variations in the ionospheric parameters could also be caused by wave disturbances of various spatial and temporal scales (including internal gravity waves) propagating into the thermosphere from the underlying atmosphere. The mesoscale wave generation source at the strato-mesospheric heights was associated with baroclinic instabilities in the spatially non-uniform, high-velocity winter jet stream. Highlights • Ionosphere response on winter stratosphere/mesosphere jet stream. • Eurasian ionosonde chain data are used for ionosphere study. • Specific longitudinal ionosphere dynamics over jet stream was found. • Different mechanisms of thermosphere [O]/[N 2 ] ratio change are discussed. [ABSTRACT FROM AUTHOR]

We studied ionospheric disturbances caused by the wave-like processes in the middle atmosphere. The ionospheric data were obtained from continuous measurements with the DPS-4 vertical sounding ionosondes in Irkutsk and Norilsk over 2008–2010. The ionospheric disturbances were considered as deviations of the F 2 layer peak density variations from the daily average values. We also used ECMWF ERA-Interim reanalysis data for the middle atmosphere dynamics analysis, and the Aura MLS data on the atmospheric temperature at the stratosphere and upper mesosphere heights obtained within the above period. The analysis allowed us to reveal periods of middle-scale wave motions in the stratosphere and lower mesosphere during winter seasons in the Northern Hemisphere. The wave motions observed in the study were associated with the jet streams at the stratosphere/lower mesosphere heights localized mainly between 50 and 80°N. The middle-scale waves in the stratosphere were compared with ionospheric disturbances over two ionosonde stations in Irkutsk and Norilsk. A noticeable increase in the wave activity was found at the F 2 layer heights during the periods of stratospheric wave activity. For both stations, the maximal variability in the ionosphere F 2 layer parameters was observed in winter with the minimal variability observed in summer. The summer–winter difference was more pronounced in the case of the high-latitude ionosonde in Norilsk. [ABSTRACT FROM AUTHOR]

Abstract This study presents an analysis of geomagnetic disturbances and ionospheric electron density distribution during the 2015 St. Patrick's Day geomagnetic storm. To study those we have used the satellite-borne and ground-based observations. The St. Patrick's geomagnetic storm covers the interval of 15–23 March 2015, when solar eruptive phenomena (a long-enduring C9-class solar flare and associated CME's on 15 March) and a strong geomagnetic storm on 16–18 March (Dst dropped as strong as –228 nT) were reported. This geomagnetic storm is still the strongest one observed in the current solar cycle. The severe geomagnetic storm on 17-18 March 2015 led to complex effects on the ionosphere. We consider major features of the positive and negative ionospheric storms development at European mid- and high-latitudes. One of the interesting phenomena was observation of the positive ionospheric disturbances during the recovery phase. Using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) we examined the main physical processes that played a major role in dramatic changes of the total electron content and the F 2 layer peak electron density during this storm event. Highlights • All types of the ionospheric disturbances are very well reproduced by GSM TIP model for the 2015 St. Patrick's Day storm. • The prompt penetration electric field dominates in producing of the positive ionospheric storm only at the storm beginning, and equatorward neutral wind dominates during several hours after that. • We conclude that the neutral composition changes play the most important role in the daytime electron density increase at different latitudes during the recovery storm phase. [ABSTRACT FROM AUTHOR]

Abstract In the paper we study the ionosphere response to the March 2015 severe geomagnetic storm according to Eurasian high-middle latitude ionosonde chain. On the basis of the ionosonde chain data we have restored the time/longitude dynamics of the high-middle latitude ionosphere over the Eurasian continent. The data showed that during the main storm phase that developed in the nighttime Siberian sector, a disturbed thermosphere region was created. This region moved westward with 50–70 m/s velocity and which was registered two-three days after the storm in the Eastern and Western Europe. Characteristics of the geomagnetic field variations showed that three active zones occurred during the storm. One is shifted from the geographic pole toward magnetic pole at ∼270° longitude. Two other zones were formed symmetrically opposite to the geomagnetic pole at longitudes ∼40° and ∼130°; the major electron density depletions at these longitudes were observed in the high-middle latitude ionosphere. On the contrary, longitudinal sector ∼80–110° showed electron density maximum in quiet conditions and fast ionosphere restoration after the storm decaying. Highlights • Ionosphere response on winter stratosphere/mesosphere Jet stream. • Eurasian ionosonde chain data are used for ionosphere study. • Specific longitudinal ionosphere dynamics over jet stream was found. • Different mechanisms of thermosphere [ O ]/[ N 2 ] ratio change are discussed. [ABSTRACT FROM AUTHOR]

Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to develop a method for evaluating the ionosphere critical frequency using the IAR emission observations. Such a method may prove to be useful as an additional alternative to the basic method for probing the ionosphere using digisondes. This is especially important for auroral regions, where the presence of strong absorption, shielding by a lower layer, stratification, the presence of echoes, etc. make the sounding difficult. [ABSTRACT FROM AUTHOR]

Space radio emission is the important source of background for radio physical investigation of the ionosphere. Variations of the background signal and scintillations of the discrete radio sources allow defining some ionosphere characteristics such as plasma density variations and degree of plasma inhomogeneity. Irkutsk incoherent scatter radar (IISR) has narrow palm-like directivity diagram. With this diagram IISR scans a wide sector of elevation angles of the celestial sphere. The sweeping time of a 40° sector with 0.5° step is around several seconds. Therefore, IISR in the passive mode is capable to work as an imaging riometer. As a result of several month passive mode observations we detected a number of scintillation events and found a good agreement between the scintillation and spread-F events which were observed independently. IISR in the passive mode is also sensitive to the solar events and probably capable to observe solar radio emission objects with good time resolution and in a wide spatial range. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation of thermospheric and ionospheric response to the sudden stratospheric warming (SSW) event, which took place in January 2009. This period was characterized by low solar and geomagnetic activity. Analysis was carried out within the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP). The experimental data of the atmospheric temperatures obtained by Aura satellite above Irkutsk and ionosonde data over Yakutsk and Irkutsk were utilized as well. SSW event was modeled by specifying the temperature and density perturbations at the lower boundary of the GSM TIP model (80km altitude). It was shown that by setting disturbances in the form of a stationary planetary perturbation s=1 at the lower boundary of the thermosphere, one could reproduce the negative electron density disturbances in the F region of ionosphere during SSW events. Our scenario for the 2009 SSW event in the GSM TIP allowed to obtain results which are in a qualitative agreement with the observation data. [Copyright &y& Elsevier]