Geoeffectiveness of solar flares in magnetic crochet (sfe) production: II-Dependence on the detection method

During magnetic active periods, disturbances in the geomagnetic field can act as natural noise masking other magnetic variations of small amplitude. In this paper, the influence of these perturbations on the observation of the effects on Earth of solar flares (sfe) has been studied. The diurnal and monthly values of detected sfe have been obtained, as well as the temporal variation of the relative occurrence of events. These numbers show how the irregular distribution of the magnetic observatories is an important limitation in the efficiency of the detection method. Some considerations about the actual method used at the International Service on Rapid Magnetic Variations are finally presented.