VLF observation of D-region disturbances associated with solar flares at UKM Selangor Malaysia

The earth´s ionosphere responds rapidly to the enhanced X-rays radiation emitted from the sun during the event of solar flares. A study of monitoring the lower ionospheric electron density modifications associated with solar flare during February and April 2011 is presented. A total of 13 VLF perturbations in association with solar flare events were identified. Data from GOES satellite were used to determine the time onset and type of each of these flares. Results reveal that a X2.2 which occurred on 15 February 2011 was capable of generating perturbations, in both the amplitude and phase, on the Very Low Frequency (VLF 3 - 30 kHz) transmitter signals as high as 4.3 dB and 90 degrees. Several VLF signal perturbations due to solar flare were detected. We found a positive correlation between solar flare radiation intensity and the values of amplitude and phase perturbations. Results indicated that amplitude and phase perturbations time-correlated with the solar flare, varied from 0.5 - 4.3 dB and 2 - 90 degree respectively.