Studying travelling ionospheric disturbances from near-vertical ionosphere sounding with high temporal resolution
In this study, we analyze the near-vertical ionospheric sounding data obtained with a multipurpose digital chirp ionosonde. The ionosonde was recording ionograms once each minute. We analyzed the results of processing the datasets over three observational years from 2010 to 2012. Obtaining ionograms with a high temporal resolution allowed us to trace the dynamics and evolution of additional traces referred to as “cusps”, and also to combine ionograms with such traces into sequences. The percentage of ionograms containing cusps proved to be more than 10% of the overall number of ionograms. Thus, during daytime, the rate surpasses 30%, whereas, during nighttime, such ionograms are practically absent. The typical cusp lifetime proved to be 4-15 min, therefore, disturbed ionograms are much more rarely detected with standard vertical sounding ionosondes. The presence of such traces unambiguously evidences significant electron density horizontal gradients caused by travelling ionospheric disturbances (TIDs) with scales up to 50 km.
Problem of Topside Ionosphere Sounding Using Chirp Signals
The article presents the results of using receiving and transmitting dipole antennas with a common center for sounding the ionosphere by a chirp signal. Conclusions are drawn about the possibility of using such facilities for sounding the external ionosphere. During tests conducted on a specially designed antenna stand, it was found that the coupling coefficient of the transmitting and receiving antennas at mutual angles of 45° has a value of no more than −10 dB, and the difference of the coupling coefficients of transmitting and receiving antennas of mutual angles of 45° and 90° has a value of about 15 dB.
A global empirical model of effects of large-scale internal gravity waves in the night-time ionosphere
Abstract On the basis of an analysis of a large amount of data from the vertical ionospheric sounding stations located in the Northern half of the Eastern hemisphere, a global empirical model of variations of f 0 F 2 and the F 2 layer height associated with large-scale internal gravity waves (IGW) during magnetospheric substorms and the first few hours of magnetic storms is constructed. The model is valid for night hours in the interval from subauroral latitudes to equatorial ones for all seasons and for different levels of solar activity. The model allows one to estimate the probability, delay relative to substorm onset, amplitude and time evolution of the IGW effects in the ionospheric F region. Using this model, the main features of the IGW effect in the ionospheric F region are derived depending on season, latitude, and levels of solar and magnetic activities. It is found that the IGW probability is quite high; it increases with increases of substorm intensity and solar activity. For substorms with AE max > 1000 nT in years of solar maximum, this probability amounts to as much as 100%. The IGW amplitude also increases with increases of substorm intensity and solar activity. The IGW effect amplitude depends on solar activity nonlinearly: it increases appreciably when F 10.7 changes from 75 to 150 and almost does not vary when F 10.7 grows from 150 to 200. At high solar activity, seasonal variations are clearly exhibited: the IGW effect amplitude is noticeably greater in winter and the equinoxes than in summer. In years of solar minimum, seasonal variations are negligible. For all seasons and levels of solar and magnetic activities, the effect amplitude is greatest at subauroral latitudes and then decreases smoothly as the latitude is reduced, with a local maximum near geomagnetic latitude φ = 20 . Interpretations of some features of the effect are suggested.