Finding gravity wave source positions using the Super Dual Auroral Radar Network

Abstract

Abstract. Through the groundscatter process the Super Dual Auroral Radar (Super-DARN) has become a powerful tool for studying F region gravity waves. However, the measurement of the gravity wave position is not direct and relies on an assumption relating ground scatter distance to reflection distance. In previous studies it has been assumed that the tilting of the ionospheric reflecting layer was negligible. Hence the gravity wave distance has been calculated as if the reflecting layer was strictly horizontal. Using virtual height data from an ionosonde and ray tracing, we show that this assumption leads to a systematic error of about 16 % in the positioning of the ionospheric reflection point, with the error more than 30% on occasion. Using ray tracing, we obtained an improved relation between ionospheric reflection and ground scatter distances. With this improved distance calculation, we have found the direction and velocity for a number of gravity waves. These waves were found to be traveling equatorward, usually, with velocities between 50 and 280 m/s, in agreement with previous gravity wave observations and with the notion of filtering by the thermospheric wind. In some cases the source locations were determined by using gravity wave dispersion. These locations were found to be on the poleward side of the auroral oval during periods of weak, but observable, magnetic disturbance. Our raytracing studies found that the strongest features were due to gravity waves of 3-20 km amplitude.

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…Using this method it was found that waves typically originated near the convection reversal boundary, with the majority of the waves originating within the eastward electrojet in the afternoon sector ionosphere. However, under some circumstances the position of the wave source, determined by simple assumptions about the radio propagation path, can lead to errors of up to 30% in the range determination (Hall et al 1999;MacDougall et al 2001). Further study of wave parameters and source locations confirmed that the Earth-reflected model proposed by Samson et al (1990) adequately described the gravity wave observations of the Goose Bay SuperDARN radar (Bristow et al 1994;Huang et al 1998a;Hall et al 1999).…”

“…However, under some circumstances the position of the wave source, determined by simple assumptions about the radio propagation path, can lead to errors of up to 30% in the range determination (Hall et al 1999;MacDougall et al 2001). Further study of wave parameters and source locations confirmed that the Earth-reflected model proposed by Samson et al (1990) adequately described the gravity wave observations of the Goose Bay SuperDARN radar (Bristow et al 1994;Huang et al 1998a;Hall et al 1999). Examination of a large number of events showed waves with frequencies mainly between 0.3 mHz and 0.5 mHz, and wavelengths that ranged between 160 km and 560 km.…”

Travelling ionospheric disturbance properties deduced from Super Dual Auroral Radar measurements

“…This modeling assumes that we know the antenna pattern and that there is no absorption. Doing this modeling showed that the formula used in Hall et al (1999) had backscatter that was too strong for low elevation angles. Accordingly the formula was modi®ed for this study and for elevation angles less than 60°(the angles of importance for this study) the backscatter coe cient, relative to 0 dB for specular re¯ection, was taken as r = )30.0 + 1.0´(elevationangle )60.0) dB.…”

“…Hall et al (1999) adapted a typical backscatter formula from formulas applicable to much higher frequencies. For the present study the observed backscatter for an unperturbed ionosphere was examined.…”

“…Thus the velocity of the TID would be about half the velocity determined from the time variation of distance to the backscatter intensity maximum produced by the focusing action of the TID. This assumption that 1=2 is an appropriate factor when making TID velocity calculations was challenged by Hall et al (1999) who found, using simple raytracing analysis of TIDs, that 1/1.66 is a more suitable factor for TID velocity calculations. In this present study, we perform more extensive raytracing analysis of TID focusing and show that the appropriate proportionality factor can be close to 1.0.…”