Three‐dimensional ray‐tracing for very low latitude whistlers, taking into account the latitudinal and longitudinal gradients of the ionosphere

Abstract

Abstract. Propagation mechanism of very low latitude (geomagnetic latitude less than 20 ø ) whistlers is poorly understood, and this paper examines the propagation characteristics of nonducted propagation at very low latitudes by using three-dimensional ray-tracing for realistic ionosphere/magnetosphere models with latitudinal and longitudinal gradients and International Geomagnetic Reference Field (IGRF) magnetic model. By assuming small possible tilts (in the latitudinal and longitudinal direction) of the initial wave normal angle in the input Southern Hemisphere as in our previous paper [Ohta et al., 1997], we have found that it is possible for us to detect, at a very low latitude position in the Northern Hemisphere, some whistler rays being able to penetrate through the ionosphere and some others that are subject to total reflection and come back to the magnetosphere. By making full use of systematic analyses of ionospheric parameters (local time (LT) dependence of latitudinal and longitudinal gradients), we conclude that the LT dependence of occurrence rate of whistlers at very low latitudes can be accounted for by means of such LT dependence of the gradient (especially latitudinal), lending to a further support to our previous nonducted propagation mechanism.

Very Low Latitude Whistler‐Mode Signals: Observations at Three Widely Spaced Latitudes

“…At very low latitudes, if the whistler needed to penetrate the D region to reflect from the ground, and so echo, the attenuation would likely be too great but if it reflected from the steep vertical gradients at the bottom of the F region this would be avoided. Ohta et al () and Ohta and Hayakawa (), using 3‐D, IGRF ray tracing and the non‐ducted (~10–10°) path, came to the general conclusion that it is possible to reproduce the one‐hop and three‐hop whistlers with the observed dispersion ratio of 1:3. Singh and Hayakawa () conclude that for “the propagation mechanism of low latitude and equatorial whistlers, it is clear that most of the low‐latitude workers in India, China, and New Zealand have favored non‐ducted propagation for low‐ and very‐low‐latitude whistlers.…”

Ionospheric Effect Mitigation for Real-Time Single-Frequency Precise Point Positioning

“…Horizontal electron density gradients have been described as a common phenomenon in the middlelatitude region [18], but they have also been investigated in other regions. [19][20][21][22] attempted to introduce ionospheric gradient parameters in GPS network processing, and they found out that these parameters might absorb part of the satellite-and epoch-specific biases. Dai et al [23] has also made similar attempts to estimate ionospheric gradient parameters for ambiguity resolution, hoping that the ionospheric gradient parameters could absorb a significant amount of the spatially correlated ionospheric biases.…”