Studies of medium scale travelling ionospheric disturbances using TIGER SuperDARN radar sea echo observations

L.-S He,P L Dyson,W Wan,M L Parkinson

doi:10.5194/angeo-22-4077-2004

L.-S He, P L Dyson + Show 2 more

Open Access

https://doi.org/10.5194/angeo-22-4077-2004

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Abstract

Abstract. Seasonal and diurnal variations in the direction of propagation of medium-scale travelling ionospheric disturbances (MSTIDs) have been investigated by analyzing sea echo returns detected by the TIGER SuperDARN radar located in Tasmania (43.4° S, 147.2° E geographic; –54.6°Λ). A strong dependency on local time was found, as well as significant seasonal variations. Generally, the propagation direction has a northward (i.e. equatorward) component. In the early morning hours the direction of propagation is quite variable throughout the year. It then becomes predominantly northwest and changes to northeast around 09:00 LT. In late fall and winter it changes back to north/northwest around 15:00 LT. During the other seasons, northward propagation is very obvious near dawn and dusk, but no significant northward propagation is observed at noon. It is suggested that the variable propagation direction in the morning is related to irregular magnetic disturbances that occur at this local time. The changes in the MSTID propagation directions near dawn and dusk are generally consistent with changes in ionospheric electric fields occurring at these times and is consistent with dayside MSTIDs being generated by the Lorentz force. Key words. Ionosphere (ionospheric disturbances; wave propagation; ionospheric irregularities; signal processing)

Highlights

The ionospheric manifestations of atmospheric gravity waves (AGWs) are called travelling ionospheric disturbances (TIDs) (Munro, 1958) and medium-scale TIDs (MSTIDs) of sufficient amplitude and appropriate wavelength which cause focusing and defocusing of HF radio waves reflected at oblique incidence to the ionosphere
ΣH >σP, where σH is the Hall conductivity and σP is the Pedersen conductivity. Both transition propagation direction at 09:00 and 14:00 local time (LT) on the dayside are generally consistent with the variations of ionospheric electric fields (Friis-Christensen et al, 1985), but in the early morning sector the electric fields change their directions around 05:00 LT and medium-scale travelling ionospheric disturbances (MSTIDs) propagation directions changed at 09:00 LT
A case study showed that the method clearly identifies dominant MSTIDs propagating through radar field of view

Summary

Introduction

The ionospheric manifestations of atmospheric gravity waves (AGWs) are called travelling ionospheric disturbances (TIDs) (Munro, 1958) and medium-scale TIDs (MSTIDs) of sufficient amplitude and appropriate wavelength which cause focusing and defocusing of HF radio waves reflected at oblique incidence to the ionosphere. Many data analysis methods have been developed to determine MSTID and MSAGW parameters (such as the phase velocity, azimuth, and wavelength) from different types of radio observations (e.g. Briggs, 1968a, 1968b; Tsutsui et al, 1984; Crowley et al, 1987; Shibata, 1987; Wan et al, 1996). Tsutsui et al (1984) developed a cross spectral Fourier transform technique to determine wind velocity from an HF radar array, and Shibata (1987) and Wan et al (1996) applied the maximum entropy method in their MSTID studies using radio systems. In analyzing SuperDARN observations to detect MSTID excitation sources, Samson et al (1990) applied a cross-spectral analysis method (“MUSIC”) to time series obtained at different range gates of the Goose Bay radar.

Data analysis methods

Characteristics of MSTID propagation characteristics derived from sea echoes

Findings

Discussion

Conclusions