Simultaneous observations of some unusual whistlers and VLF hiss emission at a low L-value (L = 1.17) K.K. Singh a , J. Singh b , M. Altaf c , Ashutosh K. Singh a , S. Kumar a , A.K. Singh a, * , Shyampati d , Lalmani c a Physics Department, Banaras Hindu University, Varanasi, India b Physics Department, G.G.M. Science College, Canal Road, Jammu, India c Physics Department, National Institute of Technology, Hazratbal, Srinagar, Kashmir, India d Physics Department, Udai Pratap Autonomus College, Varanasi, India Received 12 January 2009; received in revised form 16 October 2009; accepted 21 October 2009 Abstract The purpose of this paper is to describe some unusual whistlers (doublets and triplets) and VLF hiss emission recorded simultaneously on February 18, 1998 during nighttime at a low latitude Indian ground station Jammu (geomag. lat., 22° 26 0 N; L = 1.17), and to make some discussions about their origin. The detailed structures of the observed VLF hiss emission clearly show that these emissions confined to a narrow continuous frequency band. Some times the frequency of hiss band oscillates and subsequently touches the upper edge of the first whistler component of the doublet. Detailed structures of the dynamic spectra of whistler and VLF hiss emission are briefly pre- sented. From the dispersion analysis of the whistler doublets and triplets, it is found that the individual whistlers of the doublets and triplets simultaneously observed on the same day are one-hop whistlers having propagation path along higher and closely spaced L-val- ues. Our result also shows that VLF hiss has been generated in the equatorial region of higher L-values. Generation and propagation mechanisms are briefly discussed. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: VLF emissions; Whistler doublet and triplets; Plasmaspheric parameters 1. Introduction Whistlers and emissions in very low frequency (VLF) ranges are considered to be invaluable tools in probing the plasma of ionosphere and magnetosphere. In particular whistler mode waves (VLF waves) and their interactions with energetic particles has been a subject of interest since the discovery of radiation belts. The wave–particle interac- tions occurring in the magnetosphere generate a variety of emissions in the extremely low frequency (ELF) and very low frequency (VLF) ranges. ELF/VLF emissions from the Earth’s magnetosphere in the range of few hertz to 30 kHz, both continuous or unstructured and discrete or structured in nature are very fascinating, challenging and interesting natural phenomena. Helliwell (1965) has classi- fied these emissions into hiss, discrete, periodic and quasi- periodic, chorus, hook and inverted hook, and triggered emissions. Of particular interest among, these are the steady, incoherent hiss emissions that were identified as early as a dominant contributor to the loss of radiation belt particles (Kennel and Petschek, 1966; Lyons et al., 1972). On the other hand triggered emissions exhibit a bewilder- ing variety of dynamical spectral forms and follow their apparent source e.g. a whistler, a discrete emission, a signal from transmitter or radiation from World’s power line 0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.10.016 * Corresponding author. Address: Atmospheric Research Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221 005, India. Tel.: +91 9793181266; fax: +91 0542 2368390. E-mail addresses: krishna23singh@rediffmail.com (K.K. Singh), altaf- nig@rediffmail.com (M. Altaf), sk_itvns@yahoo.co.in (S. Kumar), ab- hay_s@rediffmail.com (A.K. Singh), drlalmani@yahoo.com ( Lalmani). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 45 (2010) 790–797