Solar flare induced D region perturbation in the ionosphere, as revealed from a short-distance VLF propagation path

Details Solar flare induced D region perturbation in the ionosphere, as revealed from a short-distance VLF propagation path Solar flare induced D region perturbation in the ionosphere, as revealed from a short-distance VLF propagation path

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007georl..3403103t&link_type=abstract

Geophysical Research Letters, Volume 34, Issue 3, CiteID L03103

Astronomy and Astrophysics

Astrophysics

4

Ionosphere: Ionospheric Disturbances, Ionosphere: Modeling And Forecasting, Ionosphere: Wave Propagation (0689, 3285, 4275, 4455, 6934), Solar Physics, Astrophysics, And Astronomy: Flares

Scientific paper

Short-distance (propagation distance less than 1,000 km) VLF subionospheric propagation is, for the first time, used to study the solar flare induced D-region perturbations of the lower ionosphere. We have used two years data for a propagation path from the Japanese VLF transmitter (call sign JJI, frequency = 22.2 kHz, and located at Ebino, Kyushu) to a receiving station of Chofu, Tokyo. For the sake of comparison, we have also used the long distance VLF path (NWC-Chofu). First of all, the value of perturbation in amplitude (ΔA) for the short-distance path seems to be much more enhanced (ΔA = 8~9 dB) for this short-path than the long-distance paths previously studied. The experimental value of ΔA is found to monotonically increase with the logarithm of X-ray flux. This dependence is numerically simulated by means of the FDTD (finite difference time domain) method to deduce the D-region perturbation, {1 + C exp {-(z - z 0)2/2β 2} (C: enhancement factor, z0: reference height and β: vertical extent) (this modification seems to be much more realistic than the previous two parameter modeling in an exponential profile). The numerical computations with z0 ~60 km and β ~ 10 km have shown that the value of ΔA increase up to ~6 dB in a range of X-ray flux from C = 10 to C = 103. As the conclusion, the ΔA is closely related with the logarithm of solar X-ray flux, so that we will be able to deduce the C value from the observed ΔA value.

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