Combining TID observations: NNSS and radio interferometry data

The determination of the kinematic parameters of travelling ionospheric disturbances (TIDs) is an essential basis for their physical understanding and investigation of their possible excitation mechanisms. This paper describes a method to determine these parameters on the basis of combined radio interferometric observations and measurements of differential Doppler shift observed for NNSS satellites.The analysis of Dutch interferometric and differential Doppler observations, based on this method, shows that the average direction of propagation of a sample of medium scale TIDs observed during the first three months of 1982 and 1983 is towards about 10° west of south; the speeds and horizontal ‘wavelengths’ are typical for medium scale TIDs. The results are in satisfactory agreement with those of similar research performed at Nançay (France) more than 4 yr later and using a different methodology, but not with results obtained at Nançay during the same winter months as used in the present study. Differences may indicate that TID parameters vary with geographic location and time.