• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.39.3-39.3
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• 2010

Solar-terrestrial links in short-time scales(daily ~monthly) are extensively explored in recent years: such as a response of low cloud amounts to the Forbush decrease, a response of Northern Atlantic oscillation index to sudden increase in electric field intensity of solar wind and so on (e.g., Svensmark et al., 2009; Boberg & Lundstedt, 2002). In this study, we perform the superposed epoch analysis to see any possible response of the sea-level pressure over Korean peninsula to the fast solar wind stream. Data sets are daily values, and zero days are determined to be days when the solar wind velocity exceeds 800km/s. Average profile of superposed sea-level pressure shows a gradual increase during the first 2 days and a decrease afterward below the normal level with a low pressure condition maintained for a few days. This result indicates that the sea-level pressure may respond to the fast solar wind stream. In other words, the average profile of sea-level pressure mimics the average velocity profiles. The correlation coefficient between two average profiles is 0.80, with 2 day lag.

• Wind and Structures
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• 제17권5호
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• pp.537-552
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• 2013

Wind tunnel experiments were performed to study the wind loads on an inclined flat plate with and without a guide plate. Highly turbulent flow, which corresponded to free-stream turbulence intensity on the flat roof of low-rise buildings, was produced by a turbulence generation grid at the inlet of the test section. The test model could represent a typical solar collector panel of a solar water heater. There are up-stream movements of the separation bubble and side-edge vortices, more intense fluctuating pressure and a higher bending moment in the turbulent flow. A guide plate would result in higher lift coefficient, particularly with an increased projected area ratio of a guide plate to an inclined flat plate. The value of lift coefficient is considerably lower with increased free-stream turbulent intensity.

• Journal of Positioning, Navigation, and Timing
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• 제6권2호
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• pp.71-78
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• 2017

The sidereal day of a Global Positioning System (GPS) satellite was intended to equal one half of a sidereal day of the Earth. However, the sidereal day of GPS satellites has become unequal to one half of a sidereal day of the Earth. This is fundamentally caused by the non-sphericity of the Earth and the gravity of the Moon. The difference between sidereal days of GPS satellites and the Earth is known as a sidereal shift. The details surrounding sidereal shifts and their origins have yet to be fully understood. We calculated the periodicity of sidereal shifts for GPS satellites using broadcast ephemeris data. To conduct a periodic analysis of the sidereal shift, we employ the Lomb-Scargle periodogram method. It shows that the orbit periods of GPS satellites have small-amplitude perturbations with a 13.6-day period. In addition, we compare the GPS satellite orbit periods with the periodicity of geomagnetic indices and the solar wind parameters to identify the cause of the perturbations. Our results suggest that the solar wind stream might also affect the 13.6-day period of the sidereal shifts.

• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.439-450
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• 2009

2006년 상반기동안 GOES 10에 의해 관측된 > 2MeV의 전자에너지 채널에서 반복되는 상대론적 전자 증가 이벤트(GREE, Geosynchronous Relativistic Electron Event)가 4회 있었다. 이 현상들은 모두 코로나 구멍(Coronal hole)에서부터 나온 고속 태양풍(HSS, High Speed Solar Wind Stream)과 관련된 것으로 여겨진다. 약 27일 주기를 갖는 이 4회의 전자 증가 현상은 플럭스가 점점 증가하는 형태를 보인다. 현재까지 알려진 상대론적 전자 증가 현상의 주요 원인으로는 다음의 요소들이 언급되어 왔다: (1) 코로나 구멍과 관련된 태양풍 속도, (2) Pc5 ULF 파동, (3) 행성간 자기장(IMF, Interplanetary Magnetic Field) Bz의 남쪽 성 분, (4) 자기 부폭풍(substorm)의 발생, (5) 증가된 휘슬러 모드 코러스 파동(whistler mode chorus wave)과 (6)동압력(dynamic pressure). 따라서 이 논문에서는 2006년 상반기 동안 앞에서 언급한 6가지 현상 들을 분석하여 어느 요소가 상대론적 전자 증가 현상의 플럭스와 가장 가까운 연관성이 있는지 알아보고자 한다.

• 천문학회지
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• 제35권3호
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• pp.151-157
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• 2002

From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, $56.2\%$ of the IPSs are driven by ICME, $16.7\%$ by HSS, and $16.7\%$ of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining $10\%$ of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2007년도 한국우주과학회보 제16권1호
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• pp.72-72
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• 2007

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제22권1호
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• pp.6-23
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• 1994

A disconnection event (DE) of the cometary plasma tail is one of most spectacular phenomena observed in comets. Yet, for years it has remained one of the great unsolved problems I astronomy and space physics. The solar wind is thought to play a major role in the creation of comet plasma tail (type Ⅰ) disconnection events. The goal of this paper is to present a mechanism that explains the disconnection event in terms of the local conditions at the comet. Comparison of the solar wind conditions and 16 DEs in Halley's comet shows that DEs are associated primarily with crossings of the heliospheric sector boundary and apparently not with any other properties of the solar wind, such as a high speed stream[Yi et al., 1994]. A 3-dimensional resistive magnetohydrodynamic simulation in this paper supports this association by showing that only front-side magnetic reconnection between the reversed interplanetary magnetic fields that exist when a comet crosses the heliospheric sector boundary [Niedner and Brandt, 1978] could reproduce the morphology of a DE, including ray formation [Brandt, 1982].

• 태양에너지
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• 제7권2호
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• pp.74-85
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• 1987

Performances of 3 different aerodynamic analytical models, single multiple and double multiple stream tube, for vertical axis Darrieus turbine were analyzed comparatively. From the study it has been found that the models derived from stream tube assumptions can be useful for simple prediction of basic design characteristics of Darrieus turbine. But, for a large tip speed and solidity ratios, the models has shown a certain limit in its applicability according to the formulation scheme applied. The results have shown that for the case having large tip speed and solidity ratios the consideration due to stream conditions, such as trailing vortices or wakes, should be included for accurate prediction of the aerodynamic performances of Darrieus turbine.

• Journal of Astronomy and Space Sciences
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• 제6권1호
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• pp.17-28
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• 1989

Parker(1963)가 제사한 고전적 태양풍 이론은 항성계를 비롯한 여러 개의 항성풍 현상을 역학적으로 잘 설명하고 있다. 태양풍과 같은 함성풍의 경우에 대해서는 구형의 항성풍 구조를 갖지만, 우리 은하 내에서 발견되는 SS433제트, 외부 은하인 M87에서 볼 수 있는 쌍방 분출역내의 광학 제트와 AGN근방에서 발견되는 다양한 제트 현상은 항성풍과는 달리 좁은 공간으로 집속화(collimation)되는 것이 특징이다. 이 연구에서는 각운동량이 보존되는 회전 원반계의 경우, 유체 역학적 이론에 근거하여 이러한 제트 현상을 일으키는 계의 역학적 구조에 대하여 알아보았다. 특히 제트를 이루는 흐름의 단면적의 변화가 제트 흐름의 물리적 변화를 일으키는데 회전 원반계의 경우, 이 관계가 뚜렷이 나타나는 것을 알았다.

• 천문학회보
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• 제32권2호
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• pp.37.1-37.1
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• 2007