Ionospheric effects of two solar flares in the maximum of solar cycle 23 and in the minimum of solar cycle 24

Using data from the GPS and GLONASS navigation satellite systems, we analyze the responses of the mid-latitude ionosphere to the extreme solar flares that occurred at the maximum of solar cycle 23 (October 28, 2003) and at the minimum of solar cycle 24 (September 6, 2017) during the same season at close solar zenith angles. To obtain the response, we use the rate of change of the total electronic content, which is practically independent of characteristics of equipment and is determined only by parameters of a propagation medium (the ionosphere in our case). The ionospheric response is shown to be almost independent of the total duration of the flare. In both cases, the duration of the main response at a level of 0.5 is about 1.5-2 min, whereas the total duration of the response is about 10 min and fairly independent of solar flare importance.