‘Hisslers’: Quasi-periodic (T∼ 2 s) VLF noise forms at auroral latitudes

Abstract

The previously reported ‘hissler’ phenomenon has been studied by means of broad band VLF data from antarctic ground stations and from the polar‐orbiting Ogo 2 and Ogo 4 satellites. Hisslers are quasi‐periodic broad band VLF auroral noises that typically present a falling‐tone characteristic on frequency‐time spectrograms and often appear in minute‐long sequences with spacing between individual bursts of the order of 2 s at a given frequency. The falling tones do not usually overlap in time; instead a new one tends to develop as the previous one ends. The falling‐tone noises are a feature of auroral hiss, in that they occur during time intervals when hiss is observed at ground stations and in portions of space where hiss is observed on polar‐orbiting satellites. A survey was made of 1500 Ogo 4 magnetic loop antenna records from the vicinity of Alaska and of the Antarctic. Hisslers were observed at various points from 58° invariant latitude to the mid polar cap, occurring on approximately 40% of the passes. Hisslers were observed from Ogo 4 in various local time and latitudinal sectors of the auroral oval, but there was some evidence of a concentration near Λ=75° and in the premidnight sector. At Byrd, Antarctica (L ∼ 7), hisslers are frequently observed prior to the expansion phase of a substorm and during a part of the expansion phase when hiss is detectable on the ground. The study suggests that centers of hissler activity are present on nearly all days, that they may be somewhat localized in space, and that they may be active for periods of several hours.

Ground‐based ELF/VLF chorus observations at subauroral latitudes—VLF‐CHAIN Campaign

“…This example of falling tone chorus is similar to that reported as "hisslers" by Ungstrup and Carpenter [1974] and as magnetospheric line radiation by Neměc et al [2009]. Li et al [2011] conducted a statistical study of the propagation angle and occurrence of falling-tone chorus emissions observed by the THEMIS satellites in the magnetosphere.…”

Hisslers: Quasi‐periodic VLF noise forms observed at low latitude ground station Jammu (L = 1.17)

“…The hisslers presented in this paper are quite similar in the spectral shape observed at the auroral latitudes [ Ungstrup and Carpenter , 1974]. However, the frequency band is different and even the periodicity of hissler element is different.…”

“…The falling tones do not usually overlap in time, instead a new one tends to develop as the previous one ends. Hisslers were first noted by Morozumi and Helliwell [1966] and its characteristics have been considered in detail by Ungstrup and Carpenter [1974] using the data of Byrd (geomag. lat., 80°S, long.…”

Quasi-periodic VLF emissions observed during daytime at a low latitude Indian ground station Jammu

“…QP emissions were further classified into type-I and type-II by Sato et al (1974) on the basis of whether or not they were correlated with geomagnetic pulsations. Hiss-type emissions have been reported which show a degree of periodicity of somewhat shorter periods (from fractions of a second to several seconds), such as 'hisslers' (Ungstrup and Carpenter 1974;Singh et al 2004) and 'pulsing hiss' (Ward et al 1982;Singh et al 2005). These are largely a night phenomenon associated with sub-storm and pulsating aurora respectively (Smith et al 1998).…”