Very low frequency radio events with a reduced intensity observed by the low-altitude DEMETER spacecraft

0449132 - ÚFA 2016 RIV US eng J - Journal Article
Záhlava, J. - Němec, F. - Santolík, Ondřej - Kolmašová, Ivana - Parrot, M. - Rodger, C. J.
Very low frequency radio events with a reduced intensity observed by the low-altitude DEMETER spacecraft.
Journal of Geophysical Research-Space Physics. Roč. 120, č. 11 (2015), s. 9781-9794. ISSN 2169-9380. E-ISSN 2169-9402
R&D Projects: GA ČR(CZ) GA14-31899S
Grant - others:Rada Programu interní podpory projektů mezinárodní spolupráce AV ČR(CZ) M100421206
Institutional support: RVO:68378289
Keywords : magnetosphere * DEMETER * VLF radio events
Subject RIV: BL - Plasma and Gas Discharge Physics
Impact factor: 3.318, year: 2015
http://onlinelibrary.wiley.com/doi/10.1002/2015JA021607/full

We present results of a systematic study of unusual very low frequency (VLF) radio events with a reduced intensity observed in the frequency-time spectrograms measured by the low-orbiting DEMETER spacecraft. They occur exclusively on the nightside. During these events, the intensity of fractional hop whistlers at specific frequencies is significantly reduced. These frequencies are usually above about 3.4 kHz (second Earth-ionosphere waveguide cut-off frequency), but about 20% of events extend down to about 1.7 kHz (first Earth-ionosphere waveguide cut-off frequency). The frequencies of a reduced intensity vary smoothly with time. We have inspected 6.5 years of DEMETER data and we identified in total 1601 such events. We present a simple model of the event formation based on the wave propagation in the Earth-ionosphere waveguide. We apply the model to two selected events, and we demonstrate that the model is able to reproduce both the minimum frequencies of the events and their approximate frequency-time shapes. The overall geographic distribution of the events is shifted by about 3000 km westward and slightly southward with respect to the areas with high long-term average lightning activity.
Permanent Link: http://hdl.handle.net/11104/0250711