Abstract

Radio signals from lightning discharges such as tweeks, whistlers and emissions can be used in the study of radio wave propagations and ultimately the ionospheric/ magnetospheric conditions. In the present paper, we have used tweeks (extremely low-frequency waves) and whistlers (very low-frequency waves) as a diagnostic tool for remote sensing the mid/upper atmosphere. These ELF/VLF waves have been recorded by automatic whistler detector setup installed at our low latitude ground station, Lucknow (geomagnetic latttude = 17.60N, geomagnetic longitude = 154.50E, Mc Ilwain parameter, L = 1.10), India. Tweeks have been used to estimate the nighttime D-region electron density at the ionospheric reflection height while whistlers have provided information about magnetospheric medium parameters such as dispersion, electron density, total electron content in a flux tube and the propagation path of radio signal generated during lightning discharges. During our analysis, we obtained the existence duration of tweeks to be in the range of 10 - 55 ms, the D-region electron density were estimated from 22.51 - 132.46 cm-3 for cut-off frequencies at higher harmonics and ionospheric reflection height varied from 80 - 94.4 km. We have interpreted the relevance of cut-off frequency and relative amplitude of tweeks observed during lightning discharges and found an irregular pattern in the amplitude. Dispersion analysis on the observed whistlers was applied and we estimated the magnetospheric electron density in the equatorial region that varied between 1572 and 210 electrons/cm3 as L varied from L = 1.7 to L = 3.0. The minimum and maximum values of total electron content for observed whistlers are obtained about 4.00x1012 and 9.11x1012 electrons/cm2-tube. The obtained results have their importance in the comparative interpretation of other low latitude results and also in remote sensing the mid-latitude (magnetosphere) as the recorded whistlers have traveled at higher latitudes.