Solar flare effects at Ebre: Regular and reversed solar flare effects, statistical analysis (1953 to 1985), A global case study and a model of elliptical ionospheric currents

This paper presents the results of the analysis of geomagnetic effects of solar flares (sfe) recorded at Ebre observatory (40.8° latitude N, 0.5° longitude E) during 33 years (1953-1985). At Ebre, located near the focus latítude, two types of sfe can be observed: regular and reversed sfe. Regular sfe are those which have phase differences less than 90° with the regular diurnal magnetic variatíon of the day, S_R. Reversed sfe are those which have pháse differences greater than 90° with S_R. From these 33 years, 140 sfe events were selected and a statìstical study was performed. We found a local time dependence of tìie phase differences between the sfe and S_R, vectors. Morning hours have slightly positíve values and afteraoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90", concentrate between 10 and 12 hours. Reversed sfe show a dominant equinoctial character. Also, a weaker correlation was found between solar activity witíi reversed sfe (φ=0.47) than with regular sfe (φ=0.68). Using data from 67 observatories, we performed a global study of a sfe case, seen at Ebre as reversed sfe. In this case, in the northern hemisphere, the sfe system was about 1 hour of local tíme eastward of the S_R system and formed 4° higher in latitude. Finally, we present a model of two elliptical ionospheríc equivalent current systems with focus offset about 1 hour in local time to explain the phase difrerence between the sfe and Sq magnetíc vectors observed at Ebre. The parameters of this model have been fítted from the results of a previous statìstícal analysis from Ebre data. Spatíal and temporal distribution of the sfe and Sq vector phases are calculated with this model, and conditions for reversed sfe occurrence are predicted.