Ionospheric response to St. Patricks day geomagnetic storm of 2015
Résumé
In the present work the effects of the largest geomagnetic storm of the current solar cycle have been studied. The event started on March 17th 2015 with its main phase lasting about 18 hours and the longitudinally symmetric (SYM-H) disturbance index reaching a minimum value of -234 nT. TEC data derived from a set of approximately 200 GNSS receivers distributed worldwide have been analyzed. During the main phase of the storm very large TEC enhancements have been observed in the American sector with the exception of the Northern mid-latitudes where a TEC decrease has been detected. Subsequently, in the recovery phase, a TEC lowering has been identified mainly in the southern part of South America. In the Euro-African sector a general TEC increase has been noticed during the main phase of the storm, followed by a TEC reduction during the day after. Concerning the Asian sector, not remarkable TEC enhancements have been noticed during the day 17th, while a strong negative effect has been identified during the recovery phase on day 18th at mid latitudes in both hemispheres. In order to interpret the TEC enhancements and decreases observed in the different geographic sectors, the relevant ionospheric currents have been analyzed using the data collected by three arrays of magnetometers located in the corresponding geographic sectors. We then characterized the effects of the Prompt Penetration of the magnetospheric Electric Field (PPEF) and the Disturbance Dynamo Electric Field (DDEF) with particular focus on the low-latitude ionospheric regions. To complement the information about the ionosphere behavior during the period considered, ionosonde-derived peak parameter values have also been analyzed for a number of selected stations.