Estimation of D‐region Electron Density using Tweeks Measurements at Nainital and Allahabad

Abstract

Lightning generated radio atmospheric that propagates over long distances via multiple reflections through the boundaries of the Earth‐ionosphere waveguide (EIWG), shows sharp dispersion near the cut‐off frequency ∼1.8 kHz of the EIWG. These dispersed atmospherics at lower frequency end are called as ‘tweek’ radio atmospherics. In order to estimate D‐region electron densities at the ionospheric reflection heights we have utilized the dispersive property of tweeks observed at low latitude Indian stations Nainital (Geomag. Lat., 20.29° N) and Allahabad (Geomag. Lat., 16.05° N). Direction finding technique has also been applied to determine the source locations of causative lightning discharge of tweeks. In this perspective, the geographic locations is determined by the intersection of two circles that are drawn by taking the travelled / propagation distance by tweek atmospherics from source location to Allahabad (ALD) and Nainital (NTL) stations. These results are in good agreement with World Wide Lightning Location Network (WWLLN) data. The average D‐region electron density along the propagation path varied in the range ∼20–35 el/cc at ionospheric reflection heights of 70–90 km. The tweek method has unique advantage of monitoring lower boundary of the D‐region over an area of several thousand of km surrounding to the receiving stations.