Observation of tweek characteristics in the mid-latitude D-region ionosphere

Lightning generated signals (tweeks) recorded at a mid-latitude station, Gakona (62.71°N, 143.99°W) Alaska, in the North America region during January-April 2011 are used to study the tweek characteristic in D-region ionosphere in the waveguide formed by the earth´s surface and the lower ionosphere. Analysis of 873 tweeks shows that equinoxes seasons has highest tweek occurrence 99.54% and lowest for winter season 0.46%. The maximum harmonic (m) of tweek recorded is mode m=4 and tweeks with m=1 are more dominant occurrence 97.59%. Tweek can be utilized to monitor the night-time D-region ionosphere using the fundamental cut-off frequency to measure the night-time variations of the lower ionosphere´s height of the D-region ionosphere along its propagation and the equivalent electron density at the reflection height. Equivalent electron densities for tweeks varies from 23-27 el/cm³ in the altitude ranged of 77 to 91 km during the local night.