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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: We present an investigation of the influence of the 27-day solar flux variations, caused by solar rotation, on the ionosphere parameters such as the F2 layer critical frequency (foF2) and the total electron content (TEC). Our observational data were obtained with the Irkutsk Digisonde (DPS-4) located at 52.3 North and 104.3 East during the period from 2003 to 2005. In addition, we use TEC data from the Global Ionosphere Maps (GIM) based on Global Positioning System (GPS) satellites. The solar radiation flux at a wavelength of 10.7cm (F10.7 index) is used as an index characterizing the solar activity level. A good correlation between observed ionosphere parameters and solar activity variations is found especially in autumn-to-winter season. We estimate the impact of the 27-day solar flux variations on the day-to-day variability and determine the time delay of the ionosphere response. [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]

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]

We studied the main morphology of the formation of summer ionospheric anomalies which includes the Weddell Sea Anomaly (WSA) and the Yakutsk Anomaly (YA) in terms of positive night-to-day foF 2 differences. For this purpose, we have for the first time used topside sounding (Interkosmos-19 satellite) and ground-based (ionosonde) data as well as results from an empirical model (International Reference Ionosphere – IRI) and from a first-principles model (Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere – GSM TIP). The main spatial morphological characteristics of the WSA and YA are similar which points to a common cause for their occurrence. Our preliminary GSM TIP model results showed that the foF 2 values at nighttime are greater than at daytime due to: (1) the horizontal plasma transport due to electromagnetic drift; (2) the vertical component of plasma transport along the geomagnetic field lines via meridional neutral wind; (3) the distribution of the neutral composition of the thermosphere. [ABSTRACT FROM AUTHOR]

Abstract: The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered using measurements of total electron content (TEC) during the magnetic storms on October 29–31, 2003, and on November 7–11, 2004, had 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 f o F2 were used for this purpose. The variations of TEC and f o F2 were similar for all events mentioned above. The previous assumption that the ionospheric region with vertical extension from 150 to 200km located near the F-layer maximum mainly contributes to the TEC variations was confirmed for the cases when the electron density disturbance at the F region maximum was not more than 50%. However, this region probably becomes vertically more extended when the electron density disturbance in the ionospheric F region is about 85%. [Copyright &y& Elsevier]