Remote sensing of D-region ionosphere using multimode tweeks

Abstract

Lightning discharges radiate electromagnetic waves in a wide frequency range, with maximum energy in extremely low frequency/very low frequency band. A part of the radiated extremely low frequency/very low frequency wave energy is trapped in the Earth-ionosphere waveguide and travels thousands of kilometers in different modes with lower attenuation. Amplitude, frequency and phase of these waves are used to study the less explored D-region ionosphere at lower latitudes. Extremely low frequency/very low frequency observations are recorded continuously by automatic whistler detector setup installed at low-latitude Indian station Lucknow (Geom. lat. 17.6°N; long. 154.5°E). In total, 149 cases of tweeks having modes ranging from 3 to 6 have been recorded by automatic whistler detector during December 2010 and analyzed. Result shows that the propagation distance in the Earth-ionosphere waveguide lies between 1.1 and 9.4 Mm. The electron density in the lower D-region varies between 25 and 150 cm -3 . The upper boundary of the waveguide varies between 80 and 95 km. The reported results are in good agreement with the earlier measurements at different latitudes and longitudes.

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