• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.33.2-33.2
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• 2008

Korea Astronomy and Space Science Institute (KASI) is developing an empirical model for Korean Space Weather Prediction Center (KSWPC). This model predicts the geomagnetic storm strength (Dst minimum) by using only CME parameters, such as the source location (L), speed (V), earthward direction (D), and magnetic field orientation of an overlaying potential field at CME source region. To derive an empirical formula, we considered that (1) the direction parameter has best correlation with the storm strength (2) west $15^{\circ}$ offset from the central meridian gives best correlation between the source location and the storm strength (3) consideration of two groups of CMEs according to their magnetic field orientation (southward or northward) provide better forecast. In this talk, we introduce current status of the empirical storm prediction model development.

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.32.2-32.2
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• 2007

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.295-302
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• 2004

Magnetic storms are almost always accompanied with substorms or substorm-like disturbances. Understanding the nature of the storm-time substorm is important for the currently critical issue of the storm-substorm relation. In this work we have done a statistical analysis in a straightforward way to see whether the storm-time substorms are preferably spontaneous or triggered. On the basis of 301 storm-time substorms selected for this work, we have found that the occurrence of about $28\%$ of them was spontaneous while only $6.5\%$ were associated with a clear trigger(s). The rest of the events were mostly associated with complex variations of IMF. The significant percentage for the spontaneous substorms implies that the possibility of finding a storm without a substorm is greatly reduced due to the spontaneous occurrence of the substorm even when the solar wind and IMF condition remains completely steady during the storm time.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.33-33
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• 2013

We are developing empirical space weather (solar flare, solar proton event, and geomagnetic storm) forecast models based on solar data. In this talk we will review our main results and recent progress. First, we have examined solar flare (R) occurrence probability depending on sunspot McIntosh classification, its area, and its area change. We find that sunspot area and its increase (a proxy of flux emergence) greatly enhance solar flare occurrence rates for several sunspot classes. Second, a solar proton event (S) forecast model depending on flare parameters (flare strength, duration, and longitude) as well as CME parameters (speed and angular width) has been developed. We find that solar proton event probability strongly depends on these parameters and CME speed is well correlated with solar proton flux for disk events. Third, we have developed an empirical storm (G) forecast model to predict probability and strength of a storm using halo CME - Dst storm data. For this we use storm probability maps depending on CME parameters such as speed, location, and earthward direction. We are also looking for geoeffective CME parameters such as cone model parameters and magnetic field orientation. We find that all superstorms (less than -200 nT) occurred in the western hemisphere with southward field orientations. We have a plan to set up a storm forecast method with a three-stage approach, which will make a prediction within four hours after the solar coronagraph data become available. We expect that this study will enable us to forecast the onset and strength of a geomagnetic storm a few days in advance using only CME parameters and the WSA-ENLIL model. Finally, we discuss several ongoing works for space weather applications.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.80-80
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• 2003

서브스톰이 진행될 때 극지방의 지자기 교란은 대류 제트 전류와 서브스톰 전류 쐐기로 구성되는 오로라 제트 전류에 기인한다. 이들은 전기장 강화를 뜻하는 AU 지수와 전기 전도도 강화를 뜻하는 AL 지수로 나타낼 수 있다. 이들 AU, AL 지수와 자기폭풍의 정도를 나타내는 Dst 지수와의 상관관계를 구해봄으로써 서브스톰이 자기폭풍의 형성에 어떻게 기여하는지 조사하였다. 이를 위하여 월별 누적 AU, 누적 │AL│ 값을 구한 뒤 월별 누적 Dst 와의 상관관계를 구하였다. 한편 IMF(Interplanetary Magnetic Field)의 남쪽 자기장 성분으로부터 지구 자기장 내에 강력한 전기장이 형성되어 자기폭풍을 형성한다는 견해가 있다. 전기장 E=V(태양풍 속도)$\times$Bs(IMF의 남쪽 자기장 성분)으로 나타낼 수 있으므로 이로부터 구한 월별 누적 전기장과 누적 Dst 값을 비교해 봄으로써 자기권 대류가 자기폭풍 형성에 어느 정도 기여하는지 조사하였다. 본 연구를 위하여 1966년부터 1987년까지 20년간의 AE(AU, AL) 지수를 이용하였으며 IMF 자료는 ACE 위성이 제공하는 행성간 자기장 자료로 1997년부터 2002년까지의 자료를 이용하였다. 본 연구의 결과는 현재 논쟁이 되고 있는 storm-substorm의 인과관계를 보다 잘 규명할 것으로 기대된다.

• Bulletin of the Korean Space Science Society
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• 2001.11a
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• pp.40-40
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• 2001

• Journal of Astronomy and Space Sciences
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• v.25 no.2
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• pp.113-128
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• 2008

Solar wind dynamic pressure enhancements are known to cause various types of disturbances to the magnetosphere. In particular, dynamic pressure enhancements may affect the evolution of magnetic storms when they occur during storm times. In this paper, we have investigated the statistical significance and features of dynamic pressure enhancements during magnetic storm times. For the investigation, we have used a total of 91 geomagnetic storms for 2001-2003, for which the Dst minimum $(Dst_{min})$ is below -50 nT. Also, we have imposed a set of selection criteria for a pressure enhancement to be considered an event: The main selection criterion is that the pressure increases by ${\geq}50%\;or\;{\geq}3nPa$ within 30 min and remains to be elevated for 10 min or longer. For our statistical analysis, we define the storm time to be the interval from the main Dst decrease, through $Dst_{min}$, to the point where the Dst index recovers by 50%. Our main results are summarized as follows. $(i){\sim}$ 81% of the studied storms indicate at least one event of pressure enhancements. When averaged over all the 91 storms, the occurrence rate is ${\sim}$ 4.5 pressure enhancement events per storm and ${\sim}$ 0.15 pressure enhancement events per hour. (ii) The occurrence rate of the pressure enhancements is about three times higher for CME-driven storm times than for CIR-driven storm times. (iii) Only 21.1% of the pressure enhancements show a clear association with an interplanetary shock. (iv) A large number of the pressure enhancement events are accompanied with a simultaneous change of IMF $B_y$ and/or $B_z$: For example, 73.5% of the pressure enhancement events are associated with an IMF change of either $|{\Delta}B_z|>2nT\;or\;|{\Delta}B_y|>2nT$. This last finding suggests that one should consider possible interplay effects between the simultaneous pressure and IMF changes in many situations.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.90.1-90.1
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• 2012

Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in-depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time-dependent 3-D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch-angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch-angle scattering by plasmaspheric hiss inside the plasmasphere. We provide a detailed description of simulations for each of the GEM storm events.

• Journal of Astronomy and Space Sciences
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• v.32 no.3
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• pp.181-187
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• 2015

Storm sudden commencements (SSCs) occur due to a rapid compression of the Earth's magnetic field. This is generally believed to be caused by interplanetary (IP) shocks, but with exceptions. In this paper we explore possible causes of SSCs other than IP shocks through a statistical study of geomagnetic storms using SYM-H data provided by the World Data Center for Geomagnetism - Kyoto and by applying a superposed epoch analysis to simultaneous solar wind parameters obtained with the Advanced Composition Explorer (ACE) satellite. We select a total of 274 geomagnetic storms with minimum SYM-H of less than -30nT during 1998-2008 and regard them as SSCs if SYM-H increases by more than 10 nT over 10 minutes. Under this criterion, we found 103 geomagnetic storms with both SSC and IP shocks and 28 storms with SSC not associated with IP shocks. Storms in the former group share the property that the strength of the interplanetary magnetic field (IMF), proton density and proton velocity increase together with SYM-H, implying the action of IP shocks. During the storms in the latter group, only the proton density rises with SYM-H. We find that the density increase is associated with either high speed streams (HSSs) or interplanetary coronal mass ejections (ICMEs), and suggest that HSSs and ICMEs may be alternative contributors to SSCs.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.94.2-94.2
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• 2013

We studied the precipitation of magnetospheric energetic electrons into the Earth's atmosphere during magnetic storm times using precipitating electron flux data from the MEPED on board the NOAA Polar Orbiting Environmental Satellites (POES) low.altitude satellite, NOAA-16. We identified a total of 84 storm events between 2001 and 2012 using SYM-H index. We have done a superposition of precipitating electron fluxes for each of three energy ranges (i.e., e1: > 30 keV, e2: > 100 keV, e3: > 300 keV) for the identified storm times. The results show that the fluxes start to increase before the main phase of storm for all energy ranges and reach a maximum level just before the time of SYM-H minimum value. The precipitation timescales are energy-dependent, being shorter for lower energy, ~4.67 hours for e1, ~7.93 hours for e2 and ~26.5 hours for e3. The precipitating fluxes decline during the recovery phase of the storms. We examined the L shell dependence of the precipitating electron flux during the main phase. We found that statistically the precipitation fluxes are dominantly seen at L of ~ 3-4 or higher. This L value roughly corresponds to the plasmapause location during the main phase. Thus the results imply that the electron precipitation mainly occurs outside of the plasmapause. In addition, we classified the storm events by their strength and examined the dependence of precipitation on storm intensity. We found that the electron precipitation occurs on a faster time scale and penetrate into inner L shell region for a stronger storm.