Propagation modes of low- and very-low-latitude whistlers

Upper atmospheric remote sensing using ELF – VLF lightning generated tweek and whistler sferics

“…The propagation mechanisms of low latitude whistlers have been a subject of controversy over the years. Some researchers have supported non-ducted PL mode of propagation in the presence of negative latitudinal electron density gradient in the ionization (Kumar et al, 2007 and references therein;Singh and Hayakawa, 2001). Recently, based on correlation between observed low-latitude whistlers and lightning activity detected by the World-Wide Lightning Location Network near the conjugate point (geography 9.87°S, 83.59°E) of station Allahabad, India, Gokani et al (2015) have shown a possibility of ducted mode of propagation even for such very low latitude whistlers.…”

“…At mid (30 o -60 o ) and high (> 60 o ) latitudes both satellite and ground based whistler data have been extensively exploited to probe the plasmasphere. At low latitudes (< 30 o ) whistler data have not been used to determine plasmaspheric parameters, the main reason being that the propagation mechanism of low latitude whistlers cannot be determined from the whistler spectra (Singh and Hayakawa, 2001). This is because the nose frequency of such whistlers is higher than 100 kHz, well above the frequency range of the receiver.…”

“…Several authors have suggested extrapolation methods to determine the f n of ducted whistlers whose nose is not visible (Dowden and Allcock, 1971;Helliwell, 1965;Sazchin et al, 1992). However, nose extension methods assume field-aligned ducted propagation and do not apply to PL mode low latitude whistlers (Singh and Hayakawa, 2001). We look at the possibility of determining the plasmaspheric parameters from the whistlers shown in Figure 3 .…”

“…Storey (1953) predicted that the path of whistler propagation was more or less aligned with the Earth's magnetic field and extended between the hemispheres. Many researchers have reported a good number of whistlers at the low latitudes from their nighttime observations Hayakawa et al, 1990;Singh et al, 1998;Singh and Hayakawa, 2001;Kumar et al, 2007). However, the propagation characteristics of low latitude whistlers are not properly understood yet and have been the subject of controversy for a long time.…”

“…However, the propagation characteristics of low latitude whistlers are not properly understood yet and have been the subject of controversy for a long time. There is a growing consensus in favor of the non-ducted pro-longitudinal (PL) mode of propagation for nighttime whistlers (Singh and Hayakawa, 2001); however, in some cases whistlers propagating in ducted mode have also been observed at low latitudes . One such whistler has been observed at our low latitude station.…”