The paper describes a program for automatic processing of the lowest observed frequency (LOF) during solar flares, based on the analysis of oblique-incidence sounding (OIS) ionograms by summing the amplitudes to determine the useful signal area on the ionogram depending of the frequency. LOF is defined as the frequency at which the relative increment of the sums of amplitudes from the side of the lowest frequencies for the first time exceeds the level of 0.1. The operation of the program is described on the example of solar X-ray flares on February 25, 2014 and October 2, 2015.
In this work, we describe the wave ionospheric disturbance connected with large scale traveling disturbance registered using oblique incidence data over Siberian and Far Eastern regions on April 20, 2018. We analyze diurnal variations of maximum observed frequency (MOF) of HF signals. MOF variations over the paths studied have reached 10 MHz during the main phase of the magnetic storm. The wave disturbance period is 2-3 hours.
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