The relationship between Pi2 frequency and magnetic activity (substorm intensity, Kp) by using multi-point ground stations

Rui Yamaguchi[1] ,Hideaki Kawano [1],*Kiyohumi Yumoto [1]
The Circum-pan Pacific Magnetometer Network Group
Department of Earth and Planetary Sciences Faculty of Science Kyushu University[1]

In this study we focus on the dependence of the Pi2 frequency on the substorm intensity and Kp index. We have found that the frequency of the mid- to low-latitude Pi2's tends to increase with increasing substorm intensity and Kp. On the other hand, the frequency of the high-latitude Pi2's does not show clear dependencies on the substorm intensity or Kp. This result may indicate that the frequency of the mid- to low-latitude Pi2 depends on the size of the plasmaspheric cavity which changes with the geomagnetic activity, while that of high-latitude Pi2 does not depend on the magnetic activity.

It is important for understanding the substorm nature to study various phenomena simultaneously observed. In a previous study we studied the relationship between the substorm intensity, as measured by the amplitude of a positive bay at a low-latitude station, and the Pi2 amplitude at stations located from high to low latitude. There we found the following: At mid-to-low latitudes there was a quite low correlation between the substorm intensity and the Pi2 amplitude; at high latitudes there was better correlation between them. In this study we focus on the dependence of the Pi2 frequency on the substorm intensity and Kp index. We have found that the frequency of the mid- to low-latitude Pi2's tends to increase with increasing substorm intensity and Kp. On the other hand, the frequency of the high-latitude Pi2's does not show clear dependencies on the substorm intensity or Kp. This result may indicate that the frequency of the mid- to low-latitude Pi2 depends on the size of the plasmaspheric cavity which changes with the geomagnetic activity, while that of high-latitude Pi2 does not depend on the magnetic activity.