Large-scale traveling ionospheric disturbances origin and propagation: Case study of the December 2015 geomagnetic storm

We investigate the origin, occurrence, and propagation of large-scale traveling ionospheric disturbances (LSTIDs) over the European region during the 19-21 December 2015 geomagnetic storm. Analysis of the total electron content (TEC) perturbation component is supported by the ground-based Global Positioning System (GPS) and GLONASS (In Russian: GLObalnaya NAvigazionnaya Sputnikovaya Sistema) observations. The high spatial-temporal resolution mapping approach provides a very detailed specification of the ionospheric small- to large-scale disturbances associated with two major sources of the LSTIDs generation: the solar terminator passage during the quiet time and auroral activity caused by auroral particle precipitation and field-aligned currents (FACs) intensification during geomagnetic disturbances. For the first time, the joint analysis of the ionospheric plasma irregularities, FACs, and LSTIDs reveals that a zone with the intense FACs and ionospheric irregularities occurred at the same region that represent the most probable source of LSTIDs excitation. During the main phase of the storm, the LSTIDs propagated equatorward from European high latitudes to middle latitudes (35-40 degrees N) with the horizontal velocities of similar to 700-800m/s. The LSTIDs as deduced from the TEC-disturbed component had a much larger magnitude and propagate much longer distances during the daytime (sunlit part) than in the night. We found that an equatorward expansion of the strong ionospheric irregularities zone and an increase of the FACs magnitude led to a simultaneous intensification of the LSTIDs occurrence at high latitudes. The GPS ROTI (rate of TEC index) technique, a sensitive one for detection of the rapid ionospheric gradients and irregularities, could not recognize any signatures of the TIDs structures.