Changes in lower ionosphere during solar flare and storm occurred on 9 March 2012

English Abstract:

Effect of low-latitude D-region ionosphere is examined during the space weather events of solar flare and the geomagnetic storm, occurred on 9 March 2012, by means of the associated perturbations of several subionospheric VLF/LF signals. VLF data recorded at the time of solar flare show an amplitude enhancement of 2.5dB and a strong fluctuation in the amplitude of the VLF signals during the recovery phase of the flare event, which is due to geomagnetic storm and persisted through the end of the data-recording period. Further, signal absorption is seen during recovery. We suggest that both the subsequent fluctuations and signal absorption were associated with variations in the precipitation flux of energetic electrons onto the upper atmosphere due to storm. The occurrence rate of lightning-induced electron precipitation (LEP) events, as recorded on several VLF/LF signals as well as tweek analysis results were seen to be highly variable with geomagnetic activity on the day. Quantitative modeling of subionospheric VLF/LF wave propagation incorporating energetic electron flux measurements yield results consistent with the variations in the VLF signal amplitude observed.