1Indian Centre for Space Physics, 43-Chalantika, Garia Station Road, Kolkata-700084, India
2S N Bose National Centre for Basic Sciences, JD Block, Salt Lake, Kolkata-700098, India
Received: 03 Dec 2012 – Discussion started: 07 Mar 2013
Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.
Revised: 25 Jul 2013 – Accepted: 25 Jul 2013 – Published: 16 Sep 2013
Palit, S., Basak, T., Mondal, S. K., Pal, S., and Chakrabarti, S. K.: Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry, Atmos. Chem. Phys., 13, 9159-9168, doi:10.5194/acp-13-9159-2013, 2013.