Investigation of the D-region ionosphere characteristics using tweek atmospherics at low latitudes

Tweek atmospherics emitted from lightning discharges can be utilized to monitor the night-time D-region ionosphere. This paper presents the observation of tweek atmospherics received at Universiti Kebangsaan Malaysia (UKM) (2.55°N, 101.46°E) during August 2009 and October 2010. Analysis of 1383 tweeks demonstrates that these ELF/VLF signals travel considerable distances, up to 7200 km from the causative lightning discharges. The occurrence rates of tweeks in higher modes drop significantly from 962 for the first mode to 2 for the sixth mode due to the higher attenuation for the higher harmonic tweeks. The fundamental cut-off frequency of tweeks is used to measure the night-time variations of the lower ionosphere's height and equivalent electron density near the equatorial regions. the estimated ionosphere reflection height varies from 73 to 87 km and the estimated equivalent electron density at the reflection height varies from 24 to 28 el/cm3.