TID characterised using joint effort of incoherent scatter radar and GPS

Abstract

Abstract. Travelling Ionospheric Disturbances (TIDs), which are caused by Atmospheric Gravity Waves (AGWs), are detected and characterised by a joint analysis of the results of two measurement techniques: incoherent scatter radar and multiple-receiver GPS measurements. Both techniques to measure TIDs are already well known, but are developed further in this study, and the strengths of the two are combined, in order to obtain semi-automatic tools for objective TID detection. The incoherent scatter radar provides a good vertical range and resolution and the GPS measurements provide a good horizontal range and resolution, while both have a good temporal resolution. Using the combination of the methods, the following parameters of the TID can be determined: the time of day when the TID occurs at one location, the period length (or frequency), the vertical phase velocity, the amplitude spectral density, the vertical wavelength, the azimuth angle of horizontal orientation, the horizontal wavelength, and the horizontal phase velocity. This technique will allow a systematic characterisation of AGWTIDs, which can be useful, among other things, for statistical analyses.The presented technique is demonstrated on data of 20 January 2010 using data from the EISCAT incoherent scatter radar in Tromsø and from the SWEPOS GPS network in Sweden. On this day around 07:00-12:00 UT, a mediumscale TID was observed from both data sets simultaneously. The TID had a period length of around 2 h, and its wave propagated southeastward with a horizontal phase velocity of about 67 m s −1 and a wavelength of about 500 km. The TID had its maximum amplitude in Tromsø at 10:00 UT. The period length detected from the GPS results was twice the main period length detected from the radar, indicating a different harmonic of the same wave. The horizontal wavelength and phase velocity are also estimated from the radar results using Hines' theory, using the WKB approximation to account for inhomogeneity of the atmosphere. The results of this estimate are higher than those detected from the GPS data. The most likely explanation for this is that Hines' theory overestimated the values, because the atmosphere was too inhomogeneous even for the WKB approximation to be valid.

A statistical study of internal gravity wave characteristics using the combined Irkutsk Incoherent Scatter Radar and Digisonde data

“…Similar results for TIDs with over 1-h periods have been obtained by other researchers (Ma et al, 1998;Vadas and Nicolls, 2008). The reason for this disagreement may be due to the interaction of TIDs with the neutral wind.…”

“…Using the model medium parameters (e.g. the Brunt-Vaisala period), we can obtain the wind along the TID propagation direction under the assumption that the dispersion relation is valid, as it has been done by Vadas and Nicolls (2008). However, the wind velocity estimations using this approach from single measurements may considerably (up to sign reversal) differ from model velocities, and we can not verify the estimations.…”

“…Determining the TID elevation angle can be quite a challenge because this requires measurements of disturbance vertical profiles at ionospheric heights at least at three spaced points simultaneously. This objective can be best achieved through the use of incoherent scatter radars with rapid electronic beam-steering capability or complexes of radio physical equipment with different principles of operation (Ratovsky et al, 2008;van de Kamp et al, 2014). One of the first verifications of the dispersion relation for IGW was made by Williams et al (1982).…”

Sodankylä ionospheric tomography data set 2003–2014

“…These methods are well-established, but due to the relatively low inclination of 55 • , they do not measure directly the high-latitude ionosphere and provide information essentially southwards from the receiver sites. Therefore, when studying, e.g., travelling ionospheric disturbances at high latitudes, the wave structures can be distinguished in instantaneous snapshots but following their propagation is difficult (van de Kamp et al, 2014). Moreover, the GPS altitude is so high that the measurements include almost the entire plasmasphere.…”

“…Indirect measurements of the height (hmF2) of the ionospheric F2 peak have been studied by a number of authors (see e.g. Bremer, 1992Bremer, , 1998Ulich and Turunen, 1997;Upadhyay and Mahajan, 1998;Cnossen and Franzke, 2014). The hmF2 values are derived empirically using routinely scaled ionograms.…”