Search

Abstract: Regular features of the polar ionosphere have been studied using its local empirical model of the electron density distribution in the bottomside ionosphere. The local empirical model was derived from the hand-scaled ionogram data recorded by DPS-4 Digisonde at Norilsk, Russia (69.4N, 88.1E; 60N GLAT, 166E GLON) for a 6-year period from December, 2002 to December, 2008. The paper describes the technique used to build the local empirical model and discusses its diurnal, seasonal, and solar activity specifications in comparison with the standard IRI-2007 climatological model for the same period of time, long-term observations from the European Incoherent Scatter UHF radar (1988–1999), and the high-latitude ionosondes data. Primary focus of the paper is behavior of the three F2 layer parameters: the F2 peak density (NmF2), the peak height (hmF2) and the bottomside thickness (B0). Special emphasis of the paper is the analysis of the winter anomaly manifestation at Norilsk and the peculiar diurnal–seasonal behavior of hmF2 under low solar activity, named as a “polar day effect”. [Copyright &y& Elsevier]

Abstract: The topside ionosphere parameters are studied based on the long-duration Irkutsk incoherent scatter radar (52.9N, 103.3E) measurements conducted in September 2005, June and December 2007. As a topside ionosphere parameter we chose the vertical scale height (VSH) related to the gradient of the electron density logarithm above the peak height. For morphological studies we used median electron density profiles. Besides the median behavior we also studied VSH disturbances (deviations from median values) during the magnetic storm of September 11th 2005. We compared the Irkutsk incoherent scatter radar data with the Millstone Hill and Arecibo incoherent scatter radar observations, the IRI-2007 prediction (using the two topside options) and VSH derived from the Irkutsk DPS-4 Digisonde bottomside measurements. [Copyright &y& Elsevier]

Abstract: The diurnal and seasonal variations of F2 layer characteristics (critical frequency, peak height and bottomside thickness) over Irkutsk, Russia (52.3N and 104.3E) are studied by the method of running medians. The comparison with the IRI-2001 model during the decrease in solar activity in 2003–2006 revealed cases of both close agreement and systematic differences between predictions and observations. The systematic difference is not the only reason for disagreement between IRI and observations; there are also intrayear variations which are not associated with seasonal behavior. The period of observation was too short to make conclusions about solar activity dependence of the noon bottomside thickness and the modification of its diurnal behavior with decreasing solar activity. [Copyright &y& Elsevier]

Abstract: Ionospheric characteristics derived from one year of ionograms recorded by a recently installed digisonde at Irkutsk, Russia (52.5N, 104.3E) are compared with the IRI-2001 model predictions. We tested alternative ways of solar activity specification in IRI to improve its prediction quality. In addition to the standard technique of using 12 monthly average sunspot numbers, R 12, we also used monthly average and daily noon Rz and F10.7 index values available at the World Data Centers and elsewhere. Comparison of model to observations for monthly medians of major ionospheric characteristics and day-to-day variations of mean daily foF2 values is discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the results of analyzing the experimental data from the Irkutsk incoherent scatter radar, GPS receiver in Yakutsk, digital ionosounders for vertical- and oblique-incidence sounding combined with auroral images during geomagnetic disturbances as a consequence of high flaring activity of the Sun from 19 to 29 of October, 2003. Overall the observations can be interpreted in terms of the thermosphere storm model and main ionospheric trough motion. At once the negative critical frequency disturbance observed during the major storm on October 29 can not be explained in terms of the noted models. [Copyright &y& Elsevier]