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.
Vertical ionosphere sounding using continuous signals with linear frequency modulation
Consideration of the digital chirp sounder design for the modern systems of a geophysical monitoring, communication channels state forecasting and the research problems solution is given. Given the comparative results of pulsed and of continuous signal vertical sounding ionosondes.
TOPSIDE REFRACTIVE IRREGULARITIES AND TRAVELLING IONOSPHERIC DISTURBANCES.
Munro (1950) deduced from ground-based observations that traveling ionospheric disturbances (T.LD.'s) are large-scale distortions of the electron density contours, which travel through the ionosphere, and Calvert and Schmid (1964) attributed extra traces and distortions of the main echo traces, which occur near the critical frequency of topside ionograms, to refractive effects associated with large-scale irregularities. In an examination of topside and sub-peak ionograms recorded close in position and time, it was found that on a number of occasions refractive effects occurred on topside ionograms, when manifestations of T.LD.'s were observed on sub-peak ionograms (Dyson 1967b).