Nighttime D-region equivalent electron density determined from tweek sferics observed in the South Pacific Region

Abstract

Atmospherics or sferics that originate from lightning discharges on propagating large distances in the Earthionosphere waveguide, particularly at the night, form dispersed sferics called tweeks. Tweeks are novel diagnostic tool to monitor the nighttime D-region ionosphere. Mean equivalent electron density n em at mean tweek reflection heights h m and electron density profile have been estimated using the higher harmonic tweeks recorded in the time between 21-03 hrs LT at Suva (18.2• S, 178.3• E), Fiji, during a period March-December 2006. The values of n em vary from 29-170 cm −3 in the altitude range of about 3.5 km at h m of about 83 km. In terms of usually used exponential electron density profile, the ionospheric reference height and the exponential sharpness factor are calculated to be 83.1 km and 0.64 km −1 , respectively. The scale height is calculated to be 1.9 km. Equivalent electron density profile of the nighttime lower ionosphere, using tweek method, shows lower values of electron density by about 20-45% than those obtained from the IRI-2001 model.

Upper atmospheric remote sensing using ELF – VLF lightning generated tweek and whistler sferics

“…Kumar et al (2009) presented the analysis of tweeks recorded during March -December 2006 for ionospheric reflection heights h and equivalent electron density n e from cut-off frequency of modes n = 1 -6 using Eqs.1 and 3, respectively. Here we use n e for the tweeks recorded during the September 2003 -July 2004 also and combined with tweek analysis of Kumar et al (2009) and present mainly the day-to-day variability of h and n e which was not attempted by Kumar et al (2008) and Kumar et al (2009). We have only used the first harmonic of tweeks which are most clear and reliable for the data analysis.…”

Seasonal variations of nighttime D-region ionosphere in 2013 solar maximum observed from a low-latitude station

“…Maurya et al (2012a) used two tweeks in 1 min at each 15 min interval during pure nights from 21:00-02:00 LT of 2010, meanwhile, Kumar et al (2009) used tweeks in 5 min at each hour interval during nights from 21:00-03:00 LT. In present work, we use the previous method of Kumar et al (2009) and Maurya et al (2012a) to obtain h and β. We calculated the mean h and n e of the first three harmonics of tweeks recorded in 2 min at every 15 min interval.…”

“…Using first three modes of tweeks, Kumar et al (2009) and Maurya et al (2012a) calculated the reference height (h ) and sharpness factor (β) by using the Wait s formula. Maurya et al (2012a) used two tweeks in 1 min at each 15 min interval during pure nights from 21:00-02:00 LT of 2010, meanwhile, Kumar et al (2009) used tweeks in 5 min at each hour interval during nights from 21:00-03:00 LT.…”

Evaluating parameters of conductivity profile of the lower ionosphere by tweek-atmospherics

“…За счет уменьшения затухания в ионосфере в спектре таких сигналов наблюдаются составляю-щие вблизи критических частот волновода, что позволяет оценить высоту отражения и ряд дру-гих параметров нижней ионосферы [7][8][9][10][11].…”

“…Метод линейной регрессии для опре-деления дальности до источника и критиче-ской частоты волновода. Определение ρ и h обычно выполняется путем подгонки этих двух параметров для получения минимального средне-квадратического отклонения экспериментальных точек, соответствующих гармонике твика в динами-ческом спектре, от теоретической зависимости (10).…”