Jongyeob Park

A climatology of medium‐scale gravity wave activity in the midlatitude/low‐latitude daytime upper thermosphere as observed by CHAMP

We report on a detailed global climatology of medium-scale (150–600 km) thermospheric gravity wave (GW) activity using mass density observations onboard the CHAMP satellite from 2001 to 2010. Our study focuses mainly on daytime (09–18 h in local time) and midlatitude/low-latitude upper thermosphere between 300 km and 400 km altitudes. Midlatitude GW activity is strongest in the winter hemisphere. GW activity during June solstice adjacent to the Andes and Antarctic Peninsula is stronger than in any other season or location. GW activity in the low-latitude summer hemisphere is stronger above continents than above oceans: especially during December solstice and equinoxes. In terms of relative density variation, GW activity is stronger during solar minimum than solar maximum. These results agree well with the characteristics of stratospheric GWs, implying that the CHAMP GWs are mainly caused by GWs from tropospheric/stratospheric processes. Using mesosphere/lower thermosphere wind observations at a Korean Antarctic station, we investigated at which altitudes the upper thermospheric GW climatology becomes visible. While the correlation is insignificant at z=82–88 km, it becomes significant for most cases at z=90–98 km, suggesting that the upper thermospheric GW climatology may start to emerge at z≥90 km.

Simultaneous Pi2 observations by the Van Allen Probes inside and outside the plasmasphere

Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L =∼ 6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L =∼ 5). VAP-B observed oscillations in the compressional magnetic field component (Bz) and the dawn-to-dusk electric field component (Ey), having high coherence with the BOH Pi2 pulsation in the H component. The H-Bz and H-Ey cross phases at VAP-B inside the plasmasphere were near −180° and −90°, respectively. These phase relationships among Bz, Ey, and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, Bz oscillations were highly correlated with BOH Pi2 pulsations with ∼−180° phase delay, and the H-Ey cross phase is near −90°. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B.

Statistical analysis of geosynchronous magnetic field perturbations near midnight during sudden commencements

When an interplanetary (IP) shock passes over the Earths magnetosphere, the geosynchronous magnetic field strength near noon is always enhanced except for the magnetopause crossing events. Near midnight, however, it increases or decreases. This indicates that the nightside magnetosphere is not always compressed by a sudden increase in the solar wind dynamic pressure. To understand midnight geosynchronous magnetic field responses to IP shocks, we statistically examined geosynchronous magnetic field perturbations, corresponding to 120 sudden commencements (SCs), observed when geosynchronous spacecraft were near midnight between 2200 and 0200 magnetic local times. Out of the 120 SCs, 107 SCs were identified by one geosynchronous spacecraft, and 13 SCs were identified by two geosynchronous spacecraft. Thus, 133 events were used in our statistical study. We observed 23 events in spring, 40 events in summer, 32 events in fall, and 38 events in winter, respectively. A statistical study of the midnight geosynchronous SC perturbations reveals the following characteristics. (1) In summer, all events show a positive enhancement (+ΔBT) in the magnetic field strength. (2) In winter, however, ΔBT exhibits a positive (+ΔBT) or negative (–ΔBT) enhancement. (3) In summer, the midnight geosynchronous SC perturbations in the BH component (positive northward) in VDH coordinates are mostly (∼88%, 35 out of 40 events) positive (+ΔBH), while the occurrence rate of the positive perturbation (∼43%) in the Bz component (positive northward) in GSM coordinates is lower than that of the negative perturbation (∼57%). (4) In winter, the negative perturbations in ΔBH (∼61%) and ΔBz (∼74%) are dominant. (5) Both the north-south components (BH and Bz) in spring and fall are scattered around zero. To explain the observations, we suggest that SC-associated cross-tail current (JSC) has a peak intensity around geosynchronous orbit and thus is a main controlling factor of midnight geosynchronous magnetic field perturbations during SCs. Specifically, we suggest that the seasonal variation of the sign of ΔBH, ΔBz, and ΔBT is due to the seasonal variation of the spacecraft position relative to JSC.

Comprehensive analysis of the flux dropout during 7–8 November 2008 storm using multisatellite observations and RBE model

We investigate an electron flux dropout during a weak storm on 7–8 November 2008, with Dst minimum value being −37 nT. During this period, two clear dropouts were observed on GOES 11 > 2 MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time and propagates into the dayside following electron drift direction. That resupply of the particles might be caused by substorm injections due to enhanced convection. We found a significant precipitation in hundreds keV electrons during the dropout. We observe electromagnetic ion cyclotron and chorus waves both on the ground and in space. We find the drift shells are opened near the beginning of the first dropout. The dropout in MeV electrons at GEO might therefore be initiated due to the magnetopause shadowing, and the followed dropout in hundreds keV electrons might be the result of the combination of magnetopause shadowing and precipitation loss into the Earths atmosphere.

Application of decision‐making to a solar flare forecast in the cost‐loss ratio situation

The conventional skill scores for evaluating flare forecast models do not take into account the effect of various cost-loss ratios. For the first time, we have applied a decision making based on skill scores to a flare forecast model in cost-loss ratio situations. For this study, we consider a flare forecast model which provides daily solar flare probabilities from 2011 to 2014. The skill scores are computed through contingency tables as a function of probability threshold (Pth) for the decision making. A value score (VS) is calculated as a function of cost-loss ratio (C/L) and Pth, which are linearly correlated with each other. The maximum values of VS are 0.57, 0.37, and 0.61 for C-, M-, and X-class flare, respectively. We expect that this study would provide a guideline to determine C/L and Pth for the better decision making in similar forecast models.

DEVELOPMENT OF DATA INTEGRATION SYSTEM FOR GROUND-BASED SPACE WEATHER OBSERVATIONAL FACILITIES

Korea Astronomy and Space Science Institute, Daejeon 305-348, KoreaE-mail: jhbaek@kasi.re.kr(Received September 06, 2013; Accepted September 27, 2013)ABSTRACT We have developed a data integration system for ground-based space weather facilities in Korea Astronomy and Space Science Institute (KASI). The data integration system is necessary to analyze and use ground-based space weather data efficiently, and consists of a server system and data monitoring systems. The server system consists of servers such as data acquisition server or web server, and storage. The data monitoring systems include data collecting and processing applications and data display monitors. With the data integration system we operate the Space Weather Monitoring Lab (SWML) where real-time space weather data are displayed and our ground-based observing facilities are monitored. We expect that this data integration system will be used for the highly efficient processing and analysis of the current and future space weather data at KASI.Key words: space weather; data integration system; ground-based observational system: solar telescope, magnetometer, VHF radar

Development of the camera lens system for total solar eclipse observation (Conference Presentation)

Korea Astronomy and Space Science Institute (KASI) has been developing the Camera Lens System (CLS) for the Total Solar Eclipse (TSE) observation. In 2016 we have assembled a simple camera system including a camera lens, a polarizer, bandpass filters, and CCD to observe the solar corona during the Total Solar Eclipse in Indonesia. Even we could not obtain the satisfactory result in the observation due to poor environment, we obtained some lessons such as poor image quality due to ghost effect from the lens system. For 2017 TSE observation, we have studied and adapted the compact coronagraph design proposed by NASA. The compact coronagraph design dramatically reduces the volume and weight and can be used for TSE observation without an external occulter which blocks the solar disk. We are in developing another camera system using the compact coronagraph design to test and verify key components including bandpass filter, polarizer, and CCD, and it will be used for the Total Solar Eclipse (TSE) in 2017. We plan to adapt this design for a coronagraph mission in the future. In this report we introduce the progress and current status of the project and focus on optical engineering works including designing, analyzing, testing, and building for the TSE observation.

Reply to comment by U. Villante and M. Piersanti on “Statistical analysis of geosynchronous magnetic field perturbations near midnight during sudden commencements”

We thank Villante and Piersanti [2014] (hereinafter referred to as VP) for their comments on our recent paper [Park et al., 2014] (hereinafter referred to as P14). The main comment in VP is that geosynchronous magnetic field perturbations near midnight during sudden commencement (SC) can be explained by different combinations of the hinging point distance and current sheet thickness. We basically agree with VP. However, we