Analysis of MSTIDs triggered by dynamical events

It is well known that the ionosphere is a highly dynamic medium, and the electron density can vary significantly within a very short period of time at a given location. One of the reasons for the irregular variations are ionospheric signatures of Atmospheric Gravity Waves (AGWs) – Travelling Ionospheric Disturbances (TIDs). TIDs are one of the major and frequent wave-like perturbations of the ionospheric plasma. Medium scale TIDs (MSTIDs) have been described as perturbations characterized by a wavelength, period and phase speed of 50–500 km, 12–60 min and 50–400 m/s, respectively. The wave-like effects of the MSTIDs are one of the main obstacles for accurate interpolation of ionospheric corrections in a medium scale reference of the Global Positioning System (GPS) networks as the ionospheric delay is almost proportional to Total Electron Content (TEC) along the signal path and inversely proportional to the frequency squared. MSTIDs are a common phenomenon from high to low latitudes.

The main objective of the T-FORS project is the development of new validated models able to issue forecasts and alerts for TIDs several hours ahead, exploiting a broad range of observations of the solar corona, the interplanetary medium, the magnetosphere, the ionosphere and lower atmosphere. This paper presents our results on the analysis of dynamic events that trigger MSTIDs. The events identified for the purposes of the analysis were such as geomagnetic disturbances, deep tropospheric convections, earthquakes and volcano eruptions. Based on the T-FORS methodologies all available data (detrended TEC, Continuous Doppler Sounding System -CDSS measurements, Digisonde vertical and oblique soundings and gradients of the electron density, reference meteorological and seismic data) were used for this analysis. The MSTIDs occurrence was recorded and analysed and propagation pattern for these events were extracted and compared with the results of the climatological model. This comparison will support the definition of alerts criteria when the detected disturbances exceed the climatology. Physical conditions that triggered enhanced MSTID activity were also analysed to compile an inventory of parameters that can be considered as early indicators of enhanced MSTIDs.