Study of lightning whistler waves observed at high L-shells on Van Allen Probes

Abstract:

Lightning produces strong broadband radio waves, called "sferics", which propagate in the Earth-ionosphere waveguide and are detected thousands of kilometers away from their source. Global real-time detection of lightning strokes including their time, location and energy, is conducted with the World Wide Lightning Location Network (WWLLN). In the ionosphere, these sferics couple into very low frequency (VLF) whistler waves which propagate obliquely to the Earth's magnetic field. In our previous work, one-to-one coincidence between lightning and whistler waves is already found by the conjunction work between WWLLN and Van Allen Probes (formerly known as the Radiation Belt Storm Probes (RBSP)). The previous global study showed a good match between WWLLN sferics and RBSP lightning whistlers at low L-shell region (L < 3). More case studies indicated that this kind of one-to-one coincidence can be extended to a high L-shell region. Since September 2012 to now (July 2015), EMFISIS instrument has already recorded 3-D waveform data with 35 ksamples/s for 527,279 and 542,346 of 6-second snapshots, respectively for RBSP-A and RBSP-B. 461,572 and 478,510 of snapshots with L-shell value larger than 3 are used in our work. In our work, we will show the distribution of lightning whistler waves at high L-shells. This talk will also explore the upper cutoff frequency of lightning whistler waves at high L-shells.