Low Latitude Whistlers: Correlation with conjugate region lightning activity and arrival azimuth determination

Abstract:

The propagation mechanism of low latitude whistlers has puzzled the scientific community for many years. One of the key to the solution is to find the characteristics of whistler source location. The present study focuses on the correlation of ~ 2000 whistlers recorded for a period of one year (December 2010 to November 2011) using AWD-AWESOME VLF receiver system at Indian low latitude station, Allahabad (Geomag. lat. 16.79^o N; L=1.08) with the lightning activity detected by World Wide Lightning Location Network (WWLLN) at and around the conjugate region (9.87° S; 83.59° E). About 63% of whistlers are correlated with the lightning strikes around conjugate region. To confirm the source region of whistlers, arrival azimuths of whistler causative sferics are determined and they are found to point towards the conjugate region. Most of the whistlers are found to be generated from the lightning strikes which are located in the thunderstorm with movement aligned in South-East direction. Moreover, the seasonal variations in spatial and temporal occurrence of whistler and lightning activities have been examined. Winter months, December, January and February are found to be dominant for the whistler activity. An inspection on the energy values of the WWLLN detected lightning strokes and whistler producing WWLLN detected lightning strikes led to a linear relationship between the two. A special focus is also given on the analysis of spectral features of low latitude whistlers by analysing the Power Spectral Density and Amplitude. The results obtained open a new window to look for the propagation mechanism of low latitude whistlers.