The range of size in amplitude and phase perturbations varies for different paths. Amplitude changes on DHO/23.40 and ICV/20.27 kHz radio signals have strong preferences to increase. In all analyzed events the phase perturbations on DHO/23.40 and ICV/20.27 kHz radio signals show an increase. The amplitude perturbations of GQD/22.10 kHz and NSC/45.90 kHz radio signals are distributed between increase and decrease, or between enhancement and attenuation, which depends on intensity of solar X-ray flux. The obtained results reveal that the phase perturbations on GQD/22.10 kHz show mainly increase and in some events decrease. The phase perturbations on NSC/45.90 kHz have a strong preference for phase increase.
We used the LWPC code for determining electron density enhancements in the D-region which were caused by flares C1 to M5.6 (1·10-6 to 5.6·10-5 Wm−2) classes that were occurred in March 2011. The unperturbed (averaged) values of β = 0.30 km−1 and H′=74 km are used along four short paths, D