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We analyzed ionospheric parameters including the critical frequency of the F2 layer (foF2), the peak height of the F2 layer (hmF2), and the scale height at hmF2 (HT) from 2006 to 2012 (ascending phase of solar activity) at Hainan (19.5° N, 109.1° E, MLat. 9.7° N), Irkutsk (52.4° N, 104.3° E, MLat. 42.5° N), and Norilsk (69.2° N, 88.0° E, MLat. 59.8° N) stations (low, middle and high latitudes). We have used manual scaled digisonde ionogram data. Studies of foF2 and hmF2 diurnal-seasonal variations continue those made earlier for East Asia. Features peculiar for the ascending phase of solar activity are mostly consistent to those for descending phase, except for the features of sunset and nighttime hmF2 variations. Features of annual and semi-annual variations recorded by a digisonde agree with those obtained by a satellite occultation and TEC map. We also obtained seasonal, diurnal, annual, and semi-annual variations of the ionospheric parameter HT (scale height at hmF2) from digisonde data, which differ from foF2 variations and hmF2 features.

The long-duration continuous Irkutsk incoherent scatter radar (ISR) measurements allowed us to obtain the monthly averaged height-diurnal variations of the electron density in the 180–600 km altitudinal range for 4 four seasons (winter, spring, summer, autumn) and for two solar activity levels (low and moderate). Considering these electron density variations as “quiet ionosphere patterns” we compared them with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) simulations and the International Reference Ionosphere (IRI) predictions. It was found that some observational features revealed from the ISR measurements are reproduced nicely by both the theoretical and empirical models, and some features agree better with the GSM TIP than with IRI. None of the models is able to reproduce a detailed multi-peak behavior of the electron density observed by ISR at ∼300 km and above for the spring and autumn under low solar activity, while for the spring the GSM TIP tends to reproduce the morning and daytime peaks at the same local times as they are seen from the ISR observations. [ABSTRACT FROM AUTHOR]

From 2003–2012 dataset of the Irkutsk DPS-4 Digisonde (52.3°N, 104.3°E), we obtained the diurnal, seasonal and solar activity pattern of the F2 peak density (NmF2) variability for both high- and low-frequency parts of the variability. The high-frequency part (periods from 0.5 to 6 h) is mainly caused by traveling ionospheric disturbances associated with internal gravity waves. The low-frequency part with periods more than 6 h is related to long-term variability. The year-to-year (solar cycle) variations of the total daytime variability were used to estimate the geomagnetic and meteorological activity contributions into the NmF2 variability. An explanation of the obtained variability pattern is proposed in terms of the geomagnetic, meteorological and wave activity contributions, and the sensitivity of the ionospheric electron density to the geomagnetic and meteorological impacts. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of the regular features of the high-, mid- and low-latitude ionosphere characteristics has been carried out using local empirical models. The local empirical models were derived from the manual scaled ionogram data recorded by DPS-4 Digisondes located at Norilsk (69N,88E), Irkutsk (52N,104E) and Hainan (19N,109E) for a 6-year period from December, 2002 to December, 2008. The technique used to build the local empirical model is described. Primary focuses are diurnal, seasonal and solar cycle variations of the peak electron density and the peak height under low solar activity and their changes with increasing solar activity. The main objective of the paper is to reveal both common and specific features of high-, mid- and low-latitude ionosphere. Based on earlier comparisons with the International Reference Ionosphere model, we analyze how the common and specific features are reproduced by this model. [Copyright &y& Elsevier]

Abstract: Using Irkutsk digisonde data obtained in 2003–2011, a morphological analysis of the G condition occurrence has been made. The G condition was found to occur during daylight hours in summer; in winter, it is extremely rare, and its appearance is associated with intense magnetic storms. In the years of moderate solar activity, the G condition is most frequently registered at Kp ⩾4, in the forenoon. During low solar activity, it can be observed under quiet geomagnetic conditions; in most cases, local time of its appearance shifts to afternoon hours. The highest percentage of the G condition occurrence (7.7–6.4%) was recorded in June and July 2008 when the levels of solar and geomagnetic activity were abnormally low. [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]

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]