Browsing by Author "Kil, Hyosub"
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Item Restricted Are plasma bubbles a prerequisite for the formation of broad plasma depletions in the equatorial F region?(American Geophysical Union, 2013-06-24) Kil, Hyosub; Lee, Woo KyoungFormation of broad plasma depletions (BPDs) at night in the equatorial F region is understood in association with plasma bubbles. However, we report BPDs that do not show a connection with bubbles. The characteristics of BPDs are investigated using the observations of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite on 31 December 2008, 28 July 2010, and 1 February 2011. On those days, BPDs are detected in the longitude regions where C/NOFS did not detect bubbles prior to the detection of BPDs. The coincident C/NOFS and radar observations over Jicamarca in Peru show the occurrence of BPDs at the time when backscatter echoes are absent and at the height below backscatter echoes. These observations indicate that bubbles are not a prerequisite for those BPDs. The detections of those BPDs can be explained by the uplift of the equatorial F region peak height above the satellite orbit.Item Restricted Broad plasma depletions detected in the bottomside of the equatorial F region: Simultaneous ROCSAT-1 and JULIA observations(American Geophysical Union, 2014-07-09) Kil, Hyosub; Kwak, Young‐Sil; Lee, Woo Kyoung; Oh, Seung-Jun; Milla, Marco; Galkin, IvanWe investigated the association of broad plasma depletions (BPDs) with plasma bubbles and ionospheric uplift in the equatorial F region using the coincident satellite and radar observations over Jicamarca in Peru. BPDs were detected by the first Republic of China satellite (ROCSAT-1) on the nights of 21 and 22 December 2002 during the period of moderate geomagnetic activity. The observations of the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere radar and an ionosonde showed that the F peak height was lifted above the ROCSAT-1 altitude (600 km) at the times of the BPD detection. The fraction of NO+ was substantial at the locations of BPDs. These observations support the association of the BPDs with the ionospheric uplift. However, the absence of large backscatter plumes at the times of the BPD detection indicates that the BPDs were not produced by a single large bubble or a merger of bubbles.Item Restricted Morphology of the postsunset vortex in the equatorial ionospheric plasma drift(American Geophysical Union, 2014-12-09) Lee, Woo Kyoung; Kil, Hyosub; Kwak, Young-Sil; Paxton, Larry J.The postsunset vortex in the equatorial ionosphere exhibits clockwise plasma motions after sunset in longitude (time) and altitude coordinates when the equatorial ionosphere is viewed looking northward. We describe the typical morphology of the postsunset vortex using incoherent scatter radar observations at Jicamarca in Peru during the previous solar maximum (2000–2002). A pronounced vortical plasma motion appears around 1700 LT along with the onset of the prereversal enhancement (PRE). The center of this vortex is located near an altitude of 270 km. A smaller‐scale vortex also appears about 0.5 ~ 1 h later at higher altitudes. However, the morphology and occurrence time of this small vortex depend on the characteristics of the coherent backscatter region. We find that the earlier vortex is the major feature of the postsunset vortices because it is repeatable, associated with the PRE, and independent to the occurrence of the coherent backscatter region.Item Restricted The zonal motion of equatorial plasma bubbles relative to the background ionosphere(American Geophysical Union, 2014-07-09) Kil, Hyosub; Lee, Woo Kyoung; Kwak, Young-Sil; Zhang, Yongliang; Paxton, Larry J.; Milla, MarcoThe zonal motions of plasmas inside equatorial plasma bubbles are different from those in the background ionosphere. The difference was explained in terms of the tilt of bubbles by recent studies, but observational evidence of this hypothesis has not yet been provided. We examine this hypothesis and, at the same time, look for an alternative explanation on the basis of the coincident satellite and radar observations over Jicamarca (11.95°S, 76.87°W) in Peru. In the observations at premidnight by the first Republic of China satellite (altitude: 600 km, inclination: 35°), plasmas inside bubbles drift westward relative to ambient plasmas. The same phenomenon is identified by radar observations. However, the relative westward plasma motions inside bubbles occur regardless of the tilt of bubbles, and therefore, the tilt is not the primary cause of the deviation of the plasma motions inside bubbles. The zonal plasma motions in the topside are characterized by systematic eastward drifts, whereas the zonal motions of plasmas in the bottomside backscatter layer show a mixture of eastward and westward drifts. The zonal plasma motions inside backscatter plumes resemble those in the bottomside backscatter layer. These observations indicate that plasmas inside bubbles maintain the properties of the zonal plasma motions in the bottomside where the bubbles originate. With this assumption, the deviation of the zonal motions of plasmas inside bubbles from those of ambient plasmas is understood in terms of the difference of the zonal plasma flows in the bottomside and topside.