Influencia de la anomalía geomagnética del Atlántico Sur (SAMA) en las variaciones geomagnéticas debidas a compresiones magnetosféricas súbitas por el viento solar

Abstract

The magnetosphere is compressed when a bubble of solar wind (enhancement of velocity, density and temperature) impinges on it: the current at the magnetopause, that balances this pressure over the geomagnetic field, is increased. The observatories at low, middle and subauroral latitudes record a sudden increase (sc) of the north (X) and horizontal (H) components of the geomagnetic field. The South Atlantic magnetic anomaly (SAMA) is a sink of trapped particles at the radiation belt during both quiet and disturbed periods. The precipitation of these particles on the D and E regions of the SAMA ionosphere during a magnetospheric compression give rise there to a higher enhancement of the sc at night in relation with others recorded at external regions. The goal of this paper is to determine if the sc amplitude at low latitudes depends of the geomagnetic field at the place, especially at the SAMA. Then, it was studied the geomagnetic response to different variations of the dynamic pressure of the solar wind produced at low latitudes. It is found that the amplitude of the sc´s not only depends on the pressure of the solar wind, but also on the temporal variation of the solar velocity, the epoch of the year, the local time, and possibly the
previous state of the geomagnetic field perturbation or the direction of the interplanetary magnetic field. Nevertheless, the amplitude of the sc recorded at VSS observatory (at the SAMA) currently is higher to those recorded at equivalent observatories by latitude or inclination: i) VSS have not the smallest variation due to a sc; ii) VSS generally records the highest amplitude among the selected observatories that are outside the SAMA, except if it is located between the midnight and the dawn (when smallest variations are recorded).