A new index for statistical analyses and prediction of travelling ionospheric disturbances

Abstract

Travelling Ionospheric Disturbances (TIDs) are signatures of atmospheric gravity waves (AGWs) observed in changes in the electron density. The analysis of TIDs is relevant for studying coupling processes in the thermosphere–ionosphere system. A new TID index ATID is introduced, which is based on an easy extension of the commonly used approach for TID detection. This TID activity index, which can be applied for individual Global Navigation Satellite Systems (GNSS) stations and also for mapping TID activity, is capable to study both Large Scale TIDs (LSTIDs) and Medium Scale TIDs (MSTIDs). ATID is well applicable for statistical analyses and investigations of the source mechanisms of TIDs. Correlation studies presented here reveal that LSTID magnitudes at mid-latitudes are well correlated with solar wind derived parameters, like the Kan-Lee merging electric field (EKL), the intermediate function (EWAV) and the modified version of the Akasufo ϵ parameter (ϵ3). Thus, the magnitude of the global solar-wind energy input into the Earth’s magnetosphere–ionosphere–thermosphere system is most relevant for the LSTID generation. The correlation with common geomagnetic activity indices shows that also sudden changes in the magnetosphere–ionosphere–thermosphere system are relevant. Good correlation results are limited to mid-latitudes. High-latitude regions are impacted by auroral processes and low-latitude regions by coupling from below and other instabilities. ATID can be used for the modelling and prediction as demonstrated with a prediction model for storm induced LSTIDs, based on solar wind observations only. Very good performance of this LSTIDs prediction model in mid-latitudes has been proven.