LAUSR

The manifestation of the most powerful flares of class X9.3 and X8.2 recorded on September 6 and 10, 2017, respectively, in the total electronic content (TEC) of the ionosphere, are analyzed. GPS observations at midlatitude stations located in the conditions of an illuminated ionosphere were used as the initial data. The ionospheric response was determined from phase measurements of the TEC value along satellite flights over the observation station. A high linear correlation was found between the amplitude of the increase in TEC (ΔТЕС) during flares and the zenith angle of the Sun for longitudinally spaced stations. For the class-X9.3 flare, ΔТЕС exceeded 3 TECU, while for the X8.2 flare, the amplitude was almost two times smaller. It is shown that this is mainly due to the different positions of flares on the solar disk. The spatiotemporal response of the ionosphere to flares was analyzed with TEC maps with a time resolution of 5 min. Errors in navigation measurements that are caused by the effects of solar flares are identified and evaluated.