• 한국정보통신학회논문지
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• 제17권2호
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• pp.309-316
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• 2013

달 탐사 통신 시스템에 영향을 미치는 요소 중 하나인 태양활동은 오는 2013년 가을에 11년 주기로 나타나는 태양 활동 극대기를 맞이하며, 이에 따라 태양 폭발 빈도와 강도가 증가할 것으로 예상되고 있다. 태양 폭발은 지구 자기권에 영향을 미쳐 과학, 방송, 통신, 군사 위성 또는 탐사선 등의 오작동, 통신 두절, 장비 고장 등을 발생시키는 원인이 될 수 있으며, 이러한 문제점은 막대한 물리적, 경제적 손실을 가져올 수 있다. 따라서 태양 폭발이 달 탐사선에 미치는 영향에 대한 분석을 수행하여 예상되는 손실을 최소화해야 할 것이다. 본 논문에서는 탐사선의 생존성을 높이고 안정적인 통신 채널 운용을 위하여 태양 폭발에 따른 지상국 - 달 탐사선 간의 통신 모델과 그 성능을 분석한다.

• Journal of Astronomy and Space Sciences
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• 제31권2호
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• pp.149-157
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• 2014

As the prediction of geomagnetic storms is becoming an important and practical problem, conditions in the Earth's magnetosphere have been studied rigorously in terms of those in the interplanetary space. Another approach to space weather forecast is to deal with it as a probabilistic geomagnetic storm forecasting problem. In this study, we carry out detailed statistical analysis of solar wind parameters and geomagnetic indices examining the dependence of the distribution on the solar cycle and annual variations. Our main findings are as follows: (1) The distribution of parameters obtained via the superimposed epoch method follows the Gaussian distribution. (2) When solar activity is at its maximum the mean value of the distribution is shifted to the direction indicating the intense environment. Furthermore, the width of the distribution becomes wider at its maximum than at its minimum so that more extreme case can be expected. (3) The distribution of some certain heliospheric parameters is less sensitive to the phase of the solar cycle and annual variations. (4) The distribution of the eastward component of the interplanetary electric field BV and the solar wind driving function BV2, however, appears to be all dependent on the solar maximum/minimum, the descending/ascending phases of the solar cycle and the equinoxes/solstices. (5) The distribution of the AE index and the Dst index shares statistical features closely with BV and $BV^2$ compared with other heliospheric parameters. In this sense, BV and $BV^2$ are more robust proxies of the geomagnetic storm. We conclude by pointing out that our results allow us to step forward in providing the occurrence probability of geomagnetic storms for space weather and physical modeling.

• 천문학회보
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• 제37권2호
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• pp.116.1-116.1
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• 2012

When an interplanetary (IP) shock passes over the Earth's magnetosphere, the geosynchronous magnetic field strength near the noon is always enhanced, while the geosynchronous magnetic field near the midnight decreases or increases. In order to understand what determines the positive or negative magnetic field response at nightside geosynchronous orbit to sudden increases in the solar wind dynamic pressure, we have examined 120 IP shock-associated sudden commencements (SC) using magnetic field data from the GOES spacecraft near the midnight (MLT = 2200~0200) and found the following magnetic field perturbation characteristics. (1) There is a strong seasonal dependence of geosynchronous magnetic field perturbations during the passage of IP shocks. That is, the SC-associated geosynchronous magnetic field near the midnight increases (a positive response) in summer and decreases (a negative response) in winter. (2) These field perturbations are dominated by the radial magnetic field component rather than the north-south magnetic field component at nightside geosynchronous orbit. (3) The magnetic elevation angles corresponding to positive and negative responses decrease and increase, respectively. These field perturbation properties can be explained by the location of the cross-tail current enhancement during SC interval with respect to geosynchronous spacecraft position.

• Journal of Astronomy and Space Sciences
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• 제39권4호
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• pp.159-167
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• 2022

Because of the small number of spacecraft available in the Earth's magnetosphere at any given time, it is not possible to obtain direct measurements of the fundamental quantities, such as the magnetic field and plasma density, with a spatial coverage necessary for studying, global magnetospheric phenomena. In such cases, empirical as well as physics-based models are proven to be extremely valuable. This requires not only having high fidelity and high accuracy models, but also knowing the weakness and strength of such models. In this study, we assess the accuracy of the widely used Tsyganenko magnetic field models, T96, T01, and T04, by comparing the calculated magnetic field with the ones measured in-situ by the GOES satellites during geomagnetically disturbed times. We first set the baseline accuracy of the models from a data-model comparison during the intervals of geomagnetically quiet times. During quiet times, we find that all three models exhibit a systematic error of about 10% in the magnetic field magnitude, while the error in the field vector direction is on average less than 1%. We then assess the model accuracy by a data-model comparison during twelve geomagnetic storm events. We find that the errors in both the magnitude and the direction are well maintained at the quiet-time level throughout the storm phase, except during the main phase of the storms in which the largest error can reach 15% on average, and exceed well over 70% in the worst case. Interestingly, the largest error occurs not at the Dst minimum but 2-3 hours before the minimum. Finally, the T96 model has consistently underperformed compared to the other models, likely due to the lack of computation for the effects of ring current. However, the T96 and T01 models are accurate enough for most of the time except for highly disturbed periods.

• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.425-438
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• 2009

ACE 위성에서 제공되는 1998년에서 2006년까지 9년간 관측된 양질의 1시간 평균 태양풍 매개변수를 이용하여 Burton et al.(1975)의 Dst 예측식을 재검토했다. 이 기간 동안 60개의 단순 발달형 자기폭풍을 골랐다. Burton et al.(1975)의 Dst 예측식의 에너지 공급항(Q)과 소멸 시간 ($\tau$)을 추정하기 위해 상기 자기폭풍 기간 동안 $Dst^*$와 $VS_s$, ${\Delta}Dst^*$와 $VS_s$ 그리고 ${\Delta}Dst^*$와 $Dst^*$의 상관관계를 구했다. 이 때 ACE 위성으로부터 지구까지 전파 시간(1시간)과 태양풍과 지구 자기권 사이의 지연 시간(0.5시간) 고려했다. 그 결과 $VB_s$ > 0.5mV/m일 때 $Q(nT/h)=-3.56VB_s$이였고, $VB_s\;{\leq}\;0.5mV/m$일 때는 Q(nT/h)=0으로 두었다(Burton et al., 1975) 그리고 $Dst^*$가 -175nT보다 작은 음의 값을 가질 때 $\tau(h)\;=\;0.060Dst^*\;+\;16.65$이고, $Dst^*$가 -175nT보다 큰 음의 값을 가질 때 $\tau(h)\;=\;6.15$로 추정됐다. 이 연구에서 얻은 Q와 $\tau$를 Burton et al.(1975)의 Dst 예측식에 대입하고 이를 이용하여 상기 60개 자기폭풍을 예측한 결과, 관측된 $Dst^*$와 예측된 $Dst^*$의 상관계수는 0.88이였다. 이를 다른 연구 결과와 비교하기 위해 Burton et al.(1975)과 O'Brien & McPherron(2000a)의 $Dst^*$ 예측 방법을 같은 자기폭풍에 적용한 결과, 관측된 $Dst^*$와 예측된 $Dst^*$의 상관계수는 각각 0.85였다. 이 연구는 기존 연구보다 다소 개선된 결과를 나타냈으며, 특히 $Dst^*\;{< \atop \sim}\;-200nT$의 강한 자기폭풍의 예측에 효과적이었다.