Ionospheric storm characteristics and capabilities for describing their potential impact on radio systems

N. Jakowski (1), C. Mayer (1), C. Borries (1), V. Wilken (1) and B. Nava (2)
(1) German Aerospace Center / Institute of Communications und Navigation, 
Kalkhorstweg 53, D-17235 Neustrelitz, Germany
(2) The Abdus Salam International Centre for Theoretical Physics / Aeronomy and Radiopropagation Laboratory,
Strada Costiera 11, 34014 Trieste, Italy

Abstract
Ionospheric storms are the result of complex solar-terrestrial interactions in the course of space weather events. The competition of numerous coupling processes result in a high individual character of each storm. Nevertheless, there are common features which are worth to be studied in particular for mitigating or forecasting ionospheric perturbation impact on radio systems such as Global Navigation Satellite Systems (GNSS). 
Long-term imaging of the Total Electron Content (TEC) over Europe and the Northern Pole area enable studying geographical, seasonal, local and universal time as well as geomagnetic and solar activity dependencies of ionospheric storms on a statistical basis. Thus, winter storms are characterised by a pronounced positive phase whereas summer storms show a deep ionization depression propagating from high to mid-latitudes.
For better understanding of perturbation mechanisms also case studies are presented, discussing horizontal perturbation features derived from 30 s sampled GPS measurements within ground based tracking networks of the International GNSS Service (IGS) and other services. Addressed are in particular storm propagation features as strength, propagation direction and velocity.  Reported are preliminary approaches for characterizing the actual ionospheric perturbation state by ionospheric perturbation indices which should be of practical relevance for reliably operating radio systems. COST 296 community is elaborating suggestions for defining such indices.