Characteristics of geomagnetic variations associated with low latitude auroras

Characteristics of geomagnetic variations associated with low latitude auroras observed in the northern part of Japan at the times of large geomagnetic storms are examined on the basis of geomagnetic records in low latitude. There appeared two types of geomagnetic disturbances observed simultaneouly with the auroral intensifications in the main phase of the storm. The first type is bay disturbance and the second, showing increases of H component in the wide longitudinal range simultaneouly, may be attributed to the magnetospheric compression. The first type is the same as the events analyzed by Tinsley et al. (1986) but the second is a newly found one. As an approach to clarify the mechanism for the first type, it is shown, using one-sec geomagnetic values, that the precipitation of low energy electrons would be generated when a Pi2 pulsation with short periods (less than about 40 seconds) occurs.