Statistical Analysis of Low-latitude Pi2 Pulsations Observed at Bohyun Station in Korea

Abstract

We statistically investigated the properties of low-latitude Pi2 pulsations using Bohyun (BOH, Mlat = 29.8°, L = 1.35) ground magnetometer data in 2008. For this 1-year interval, 582 Pi2 events were identified when BOH was in the nightside from 1800 to 0600 local times. We found the following Pi2 characteristics. (1) The occurrence distribution of Pi2s is relatively constant in local times. (2) The Pi2 frequency varies in local times. That is, Pi2 pulsations in postmidnight sector had higher frequency than in premidnight sector. (3) Pi2 power in premidnight sector is stronger than in postmidnight sector. (4) Pi2 frequency has positive correlation with solar wind speed and AE index. (5) Pi2 power has not a clear correlation with solar wind parameters. This indicates that Pi2 power is not controlled by external sources. (6) It is found that the most probable-time between Pi2 onsets is Δt ~ 37.5 min: This is interpreted to be the period between Pi2 pulsations when they occur cyclically. We suggest that Δt ~ 37.5 min is the occurrence rate of reconnection of open field lines in the tail lobe.

Keywords

• geomagnetic field
• low-latitude Pi2 pulsation
• geomagnetic activity