• 천문학회보
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• 제37권2호
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• pp.121.2-121.2
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• 2012

Several case studies reported that low-latitude Pi2 pulsations can occur under extremely quiet geomagnetic condition (Kp = 0) and that those are not associated with substorms. Until now, no statistical study has investigated Pi2 activity at low latitude during non-substorm intervals. In this study, we statistically examine the properties of Pi2 pulsations (i.e., Pi2 pulsation's power, frequency, and duration) observed at low-latitude Bohyun (BOH, L = 1.35) station in Korea. 161 Pi2s are identified during the intervals of extremely quiet geomagnetic conditions (Kp = 0-1) on November 2008. It is found that their frequencies increase as the solar wind speed increases. It is also found that the Pi2 pulsations frequently occurred periodically every ~30 min. Using solar wind data, we discuss what determines the 30-min recurrence time of Pi2 pulsations

• Journal of Astronomy and Space Sciences
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• 제30권1호
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• pp.25-32
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• 2013

We statistically investigated the properties of low-latitude Pi2 pulsations using Bohyun (BOH, Mlat = $29.8^{\circ}$, 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 ${\Delta}t$ ~ 37.5 min: This is interpreted to be the period between Pi2 pulsations when they occur cyclically. We suggest that ${\Delta}t$ ~ 37.5 min is the occurrence rate of reconnection of open field lines in the tail lobe.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.40.3-40.3
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• 2010

The most frequently suggested source for Pi2 pulsations in the inner magnetosphere (L < 4) is standing fast-mode waves trapped in the plasmasphere (i.e., plasmaspheric resonances). They have been considered as the source of low-latitude Pi2 pulsations. The plasmaspheric resonance model suggests that compressional fast-mode waves can be detected at all local times inside the plasmasphere provided reflection of the wave energy is efficient. Until now, however, there are no reports about compressional Pi2s observed in the dayside inner magnetosphere. That is, there is longitudinal limit of inner magnetosphere. In February 2008, THEMIS probes were near dawn and/or dusk sides, which are the transition regions between the nightside and dayside, in the inner magnetosphere (L = 2-4) when low-altitude Pi2s were identified at Bohyun (L = 1.35) station in Korea. Using the THEMIS electric field data, we examined if Pi2s are excited by longitudinally localized disturbances. We found that compressional Pi2s having high coherence with a low-latitude Pi2 pulsation occur on dawnside. However, any compressional pulsations in the Pi2 frequency band were not detected on duskside. This indicates that compressional Pi2s disappear near the duskside. Our observations are discussed with spatial plasmaspheric structure and possible Pi2 mechanisms.

• 천문학회보
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• 제35권2호
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• pp.51.1-51.1
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• 2010

We report an example of Pi2 pulsation exhibiting different frequency between dawn and dusk. This Pi2 pulsation occurred around 1932 UT on February 14, 2008, and was observed at low-latitude Bohyun (BOH, L = 1.35, MLT = 3.8) and Hermanus (HER, L = 1.83, MLT = 20.1) stations. The pulsation starts simultaneously at both stations but the frequency is higher at BOH than at HER. At the time of the Pi2, THEMIS-A (THA) and THEMIS-D (THD) were on dawn (L = 2.9, MLT = 5.3) and dusk (L = 2.8, MLT = 18), respectively, in the inner magnetosphere. We find a nearly identical waveform and period between THA ${\delta}Bz$ and BOH ${\delta}H$ and between THD ${\delta}Bz$ and HER ${\delta}H$ with a near $0^{\circ}$ phase delay. This observation implies that Pi2-associated fastmode wave in the inner magnetosphere is not excited globally as a single frequency at all longitudes. We suggest that the different frequency between dawn and dusk is due to dawn-dusk asymmetry of the plasmasphere.