DETECTION AND ANALYSIS OF SOLAR FLARE EFFECTS ON TWO

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Palmer Station: Global Thunderstorm Activity and its Effects on the Radiation Belts and the Lower Ionosphere


DETECTION AND ANALYSIS OF SOLAR FLARE EFFECTS ON TWO LONG VLF PATHS


D. Grubor (1), D. Sulic (2) and V. Zigman (3)

(1) Faculty of Mining and Geology, University of Belgrade, Serbia [email protected]

(2) Institute of Physics, Belgrade, Serbia, [email protected]

(3) Nova Gorica Polytechnic, Nova Gorica, Slovenia

[email protected]

An AbsPAL receiver logging the absolute phase and amplitude measurements of fixed transmitter VLF signals has been installed in Belgrade (440 38' N, 200 46' E), and it is operating about one year. The signals from two transmitters are monitored: NWC (19.8 kHz), and NAA (24 kHz), over the GCP of 12700 km and 9800 km, respectively. The NWC - Belgrade signal is directed S - W, and NAA - Belgrade signal is directed W - E, almost along the 45th parallel. The records taken in 60 s resolution regime were analyzed. The time changes of amplitude and phase on both paths show the characteristic diurnal pattern. The midday minima appear about 7 hours before UT noon for NWC signal and 1, 5 hours after UT noon, for NAA signal, indicating that the deviative absorption occurs predominantly above the middle of GCP. The solar flares effect on the signal amplitude and phase diurnal pattern can be clearly recognized: the sharp enhancement of signal amplitude of few dB, and corresponding phase perturbation within several minutes, and estimated decay time about 40 minutes. The amplitude peaks exactly match in time with peaks of X-ray (0.1 - 0.8 nm) flux, all above 10-6 W/m2, as referred by NGDC. The decay time is actually the relaxation time for lower ionosphere, determined by predominate recombination processes. Considering the known recombination rate coefficients and estimated relaxation times, we attempt to model the electron density profile disturbations in the D region, during the flares.











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Tags: analysis of, effects, analysis, detection, solar, flare