Correlation of AE activity with IMF-Bz during small geomagnetic storms Original Research Article

Since time profiles of solar wind parameters simultaneously observed by separate satellites approximately show the same variation on time scales above 30 min or more, hourly values of AE and Dst indices during two small geomagnetic storms are compared with those of IMF-Bz and solar wind pressure to study the cause of storm AE activity. At least, two large AE episodes above 600 nT occur during the two geomagnetic storms. Between the two AE increases, a low AE valley of below 300 nT coincides with a northward IMF-Bz above 3 nT. All AE increases occur during Dst decreases of the storms. The first AE increase rapidly develops above 600 nT together with the Dst decrease as the southward IMF-Bz, westward VBz, and solar wind pressure rapidly increase. In the storm main phase, the AE index rapidly increases above 800 nT associated with large southward IMF-Bz (<−6 nT). This second AE activity group is not associated with a solar wind pressure increase. Magnetospheric processses associated with the storm AE activity are discussed.