On the observations of unique low latitude whistler-triggered VLF/ELF emissions |
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| Affiliation: | 1. Department of Physics, National Institute of Technology, Srinagar 190 006, Kashmir, India;2. Department of Physics, Banaras Hindu University, Varanasi 221 005, India;1. Department of Surface and Plasma Science, Charles University, Prague, 18000, Czech Republic;2. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA;3. Physics and Astronomy Department, University of Iowa, Iowa City, IA 52242, USA;4. Smead Aerospace Engineering Sciences Department, University of Colorado, Boulder, CO 80309, USA;1. Department of Electronics and Communication Engineering, G. B. Pant Engineering College, Pauri Garhwal, Uttarakhand, India;2. School of Information and Communication Technology, Gautam Buddha University, Greater Noida, India;3. Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada |
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| Abstract: | A detailed analysis of the VLF/ELF wave data obtained during a whistler campaign under All India Coordinated Program of Ionosphere Thermosphere Studies (AICPITS) at our low latitude Indian ground station Jammu (geomag. lat. = 22° 26′ N, L = 1.17) has yielded two types of unusual and unique whistler-triggered VLF/ELF emissions. These include (1) whistler-triggered hook emissions and (2) whistler-triggered long enduring discrete chorus riser emissions in VLF/ELF frequency range during night time. Such types of whistler-triggered emissions have not been reported earlier from any of the ground observations at low latitudes. In the present study, the observed characteristics of these emissions are described and interpreted. Dispersion analysis of these emissions show that the whistlers as well as emissions have propagated along a higher geomagnetic field line path with L-values lying ∼L = 4, suggesting that these triggered emissions are to be regarded as mid-latitude emissions. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal (PL) mode. The measured intensity of the triggered emissions is almost equal to that of the source waves and does not vary throughout the period of observation on that day. It is speculated that these emissions may have been generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra. |
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