Khan-Hyuk Kim

Abstract We statistically study the local time distribution of the helium band electromagnetic ion cyclotron (EMIC) waves observed at geosynchronous orbit when geomagnetic activity was low ( K p ≤ 1). In order to identify the geosynchronous EMIC waves, we use high time resolution magnetic field data acquired from GOES 10, 11, and 12 over a 2 year period from 2007 and 2008 and examine the local time distribution of EMIC wave events. Unlike previous studies, which reported high EMIC wave occurrenc

The traveltimes of interplanetary (IP) shocks at 1 AU associated with coronal mass ejections (CMEs) can be predicted by the empirical shock arrival (ESA) model of Gopalswamy et al. [2004] based on a constant IP acceleration. We evaluate the ESA model using 91 IP shocks identified from sudden commencement (SC)/sudden impulse (SI) on the Earth and by examining the solar wind data from the ACE and WIND satellites during the period of 1997 to 2002. Out of 91 CME‐IP shock pairs, 55 events (∼60%) were

On April 13 (day 103), 2001, 0700–1400 UT, the Polar satellite experienced different plasma regimes (i.e., magnetosphere, magnetosheath, and solar wind) because of the solar wind dynamic pressure variations and its high orbital inclination near the subsolar magnetopause meridian. When Polar was in the magnetosheath, quasiperiodic spacecraft potential (SP) variations, corresponding to density variations, with a recurrence time of ∼3–10 min were observed. Using simultaneous solar wind observations

Few spacecraft observations of Pc3–4 (7–100 mHz) pulsations at L < 3 have been reported, although ground observations of the pulsations in the same L range are routine. In particular, there are no systematic spacecraft observations of compressional pulsations expected at the time of low‐latitude ground Pc3–4 pulsations that exhibit a constant frequency over a range of L . These pulsations have been attributed to fast mode waves trapped in the plasmasphere (referred to as plasmaspheric cavity

Abstract We statistically examined the plasmapause location ( L pp ) under quiet geomagnetic conditions ( K p ≤ 1) using the electron density inferred from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft potential for 2 year period (2008 and 2009). Five hundred forty‐three L pp samples were identified under steady quiet conditions with K p values ≤ 1 during 12 h prior to the plasmapause crossing. From our large data set, we determined the medians and m

Pi2 pulsations during the intervals of extremely quiet geomagnetic conditions ( Kp = 0) have been reported by Sutcliffe and Lyons [2002] . These authors observed that several Pi2 bursts occurred simultaneously at high (magnetic latitude = 71°) and low (42°) latitudes during the absence of magnetospheric substorms and found that the bursts are strongly correlated with poleward boundary intensifications (PBIs). The authors discussed the correlation between the PBI‐associated Pi2 (PBI‐Pi2) bursts a

Abstract We have statistically studied the relationship between electromagnetic ion cyclotron (EMIC) waves and cold plasmaspheric plasma ( N sp ) in the L range of 6–12 using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) data for 2008–2011. The important observational results are as follows: (1) Under quiet geomagnetic conditions ( K p ≤ 1), the maximum occurrence rate of the hydrogen (H) band EMIC waves appears in the early morning sector (0600–0900 MLT) at th

Abstract Long‐lasting (> 20 h) electromagnetic ion cyclotron (EMIC) Pc1‐Pc2 waves were observed by the Athabasca ( L =∼ 4.6) induction magnetometer and Canadian Array for Realtime Investigations of Magnetic Activity ( L =∼ 4–6) fluxgate magnetometers on 5 April 2007. These waves showed a systematic frequency change with local time, the minimum frequency near dusk, and the maximum frequency near dawn. Assuming the plasmapause as a potential source region of the waves, we estimated the plasmapa

Recently, Lee and Lysak (1999) suggested that Pi2 pulsations in the inner magnetosphere originate from plasmaspheric virtual resonances (PVR). The PVR model predicts that Pi2 pulsations are not strictly localized to the plasmasphere. Until now there have been no spacecraft observations of the PVR mode outside the plasmasphere. Motivated by the theoretical work, we examine Pi2 pulsations simultaneously observed by the Polar satellite outside the plasmapause and at the low‐latitude Kakioka ( L = 1

Abstract We present observations of electromagnetic ion cyclotron (EMIC) waves associated with a sudden commencement (SC) on 19 November 2007. In our study, we clearly showed that there was a time delay of ∼10–15 min between the SC onset and the occurrence of EMIC waves at GOES 12 and GOES 10 in the afternoon sector, while the SC‐associated EMIC wave activity observed by GOES 11 in the morning sector started almost immediately after the onset of the SC. This indicates that the EMIC wave source d

Abstract Using Lunar Prospector magnetic field data, we identify four isolated anomalies (C NA , C SA1 , C SA1 , and C WA ) within the Crisium basin. We assume the sources of the anomalies to be buried point dipoles and find that the estimated depths and radial positions are well contained within Crisium's melt pool (∼250‐km radii and ∼100‐km depth). This implies that the anomalies recorded a thermoremanent magnetization in a dynamo field at ∼3.9 Ga. We also find that the anomalies can be classi

A clear bipolar (negative/positive) signature in the E y component was observed by three spacecraft on Cluster in the magnetotail during the passage of a solar wind discontinuity on October 11, 2001 (day 284), which caused a sudden commencement (sc) on the ground. The positive E y perturbation was accompanied by the northward/dawnward plasma flow and the B x enhancement, which is the dominant magnetic field component. The estimated E y from the plasma flow and magnetic field was in good agreemen

It has been known that the Alfvén velocity plays a significant role in generation and propagation of magnetohydrodynamic (MHD) waves. Until now, however, the global distribution of the Alfvén velocity in the magnetosphere has not been reported. To determine the spatial distribution of the Alfvén velocity, we have statistically examined the THEMIS magnetic field and electron density data obtained in the L (the equatorial geocentric distance to the field line measured in Earth’s radii) range of ~

Several case studies have suggested that low‐latitude Pi2 pulsations are triggered or driven by earthward flow bursts in the magnetotail. Until now, no statistical study has investigated the causality between the flow bursts and Pi2 pulsations, so the overall significance of flow bursts to Pi2 excitation remains unclear. In this study we statistically examine the relationship between earthward flow bursts and low‐latitude Pi2 pulsations. We address the following two questions: (1) Does every flo

During the early main phase of a geomagnetic storm on 11 April 2001, the Polar satellite was inside the magnetosphere in the prenoon sector (∼1000–1100 magnetic local times) and experienced a magnetopause crossing at L ≈ 6 because of the high solar wind dynamic pressure and strong southward interplanetary magnetic field (IMF). Just before the magnetopause crossing, Polar observed cold, dense plasma. That is, the cold, dense plasma was immediately adjacent to the compressed magnetopause. Using si