Forbush decreases (FDs), as the transient event of decreasing cosmic ray (CR) intensity, show the main phase of a sudden decrease within approximately one day and the recovery phase over several days. FDs are associated with abrupt solar wind events such as interplanetary shocks (IP shocks) and magnetic clouds. FD generation is explained by drift due to the magnetic field strength and by diffusion caused by magnetic turbulence. The FDs and the IP shocks from 1998 to 2004 in the solar maximum period were chosen to determine a more effective generation of FD between drift and diffusion. Seventy FDs with a CR variation of more than 3.0% and a minimum value of less than −1.5% were selected using Oulu neutron monitor data. The Advanced Composition Explorer satellite identified 292 IP shocks and we divided them into two sections: the pre-sheath region ahead of the shock front and the post-sheath region behind the shock front. The magnetic field strength, magnetic turbulence, solar wind speed, and solar wind turbulence of the post-sheath regions were analyzed. Most (62/70) of the FDs were associated with the post-sheath regions of the IP shocks. The important factors that generated the FDs were drift by the large physical properties in the post-sheath regions and diffusion by the strong turbulence in the post-sheath regions. The increase in the magnitude of interplanetary magnetic field (IMF) shows larger in the IP shocks associated with FD (2.33 times) than in those not associated with an FD (1.70 times) between the pre-sheath and post-sheath regions. On the other hand, the increase in turbulence of IMF was the same for IP shocks associated with an FD and not associated with an FD. Although it was difficult to determine the dominant factor for the generation of FDs, the present study suggested that the drift by the magnetic field strength may play a more significant role than the diffusion by the magnetic turbulence.

타워형 집광태양열발전의 핵심요소인 헬리오스타트는 경량화를 통한 설비비 저감이 매우 중요한다. 반사판 면적 16m2의 기 존 헬리오스타트 대비 샌드위치 패널을 사용하여 무게를 50% 경량화한 헬리오스타트의 풍하중 평가를 수행하였다. 반사판이 수직, 45 도 경사인 경우에 대해 전산유체역학 해석을 하여 반사판에 작용하는 풍압을 산정하고 구조해석을 수행하여 최대응력의 발생부위 및 반사판의 변위에 의한 반사각도의 이격을 계산하였다. 45도 경사진 반사판이 바람이 불어오는 반대편으로 향한 경우가 바람을 마주보 는 배치보다 최대 풍하중이 더 크게 나타났으며, 반사판 풍하측으로의 유동박리에 의한 후류의 발달도 반사판의 배치에 따라 매우 상 이한 형태를 보였다. 경량화 모델의 경우 반사판 구동을 위한 기어의 배치를 변경하여 핵심 지지체인 기둥의 강성을 확보할 필요가 있 음을 확인하였다.

태양광 패널의 최적 경사각은 한국의 경우 위도 범위인 30∼40도로 상당히 크기 때문에 패널을 지나가는 바람은 필연적으로 유동박리가 수반된다. 본 연구에서는 유동박리가 수반되는 대기유동장 해석시 난류강도 모델링이 우수한 대와류모사(LES)를 이용하여 풍동실험용 축소모형 및 실제규모 태양광 패널에 대한 수치해석을 수행하였다. 태양광 패널에 작용하는 풍하중이 최대가 되는 풍향인 0도와 180도에 대해 해석하고 압력계수를 실측자료와 비교하였다. 패널 경사면을 타고 올라가는 풍향 0도의 경우는 실측자료와 LES로 예측한 압력계수가 잘 일치하였으나 반대로 패널에 부딪쳐 타고 내려가는 풍향 180도의 경우는 실측값과 상당한 차이가 있었다. 패널 위, 아래면의 압력계수의 차이로 정의되는 순압력계수를 산출하고 이를 건축구조기준의 독립된 편지붕의 최소 설계기준과 비교하였으며, 설계기준 범위 이내인 것을 확인하였다.

In this study, we investigate the kinetic properties of magnetic decreases observed in the solar wind at 1 AU using the Cluster observations. We study two different magnetic decreases: one with a short observation duration of 2.5 minutes and stable structure and the other with a longer observation duration of 40 minutes and some fluctuations and substructures. Despite the contrast in durations and magnetic structures, the velocity space distributions of ions are similar in both events. The velocity space distribution becomes more anisotropic along the direction parallel to the magnetic field, which differs from observations obtained at high heliographic latitudes. On the other hand, electrons show different features from the ions. The core component of the electrons shows similar anisotropy to the ions, though the anisotropy is much weaker. However, while ions are heated in the magnetic decreases, the core electrons are slightly cooled, especially in the perpendicular direction. The halo component does not change much in the magnetic decreases from the ambient solar wind. The strahl component is observed only in one of the magnetic decreases. The results imply that the ions and electrons in the magnetic decreases can behave differently, which should be considered for the formation mechanism of the magnetic decreases.

Ground Level Enhancements (GLEs) in cosmic ray intensity observed during the period of 1997-2012 have been studied with energetic solar features and disturbances in solar wind plasma parameters and it is seen that all the GLEs have been found to be associated with coronal mass ejections, hard X-ray solar ares and solar radio bursts. All the GLEs have also been found to be associated with sudden jumps in solar proton ux of energy of ≥ 60 Mev. A positive correlation with correlation coefficient of 0.48 has been found between the maximum percentage intensity (Imax%) of Ground Level Enhancements and the peak value of solar proton ux of energy (≥ 60Mev). All the Ground Level Enhancements have been found to be associated with jumps in solar wind plasma velocity (JSWV) events. A positive correlation with correlation coefficient of 0.43 has been found between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the peak value of solar wind plasma velocity of associated (JSWV) events. All the Ground Level Enhancements have been found to be associated with jumps in solar wind plasma pressure (JSWP) events. A positive correlation with correlation coefficient of 0.67 has been found between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the peak value of solar wind plasma pressure of associated (JSWP) events and of 0.68 between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the magnitude of the jump in solar wind plasma pressure of associated (JSWP) events.

This paper attempted to bridge this gap by identifying the number of flat-plate solar collectors. The characteristics of wind pressure coefficients acting on flat-plate solar collectors which are most widely used were investigated for various wind direction. Findings from this study found that the location where the maximum wind pressure coefficient occurred in the solar collector was the edge of the collector. Regarding the characteristics according to the number of collectors, the paper found that downward wind pressure coefficient of the lower edge of the collector was higher than the upward wind pressure coefficient of the upper edge of the collector in the basic module (1 piece). However, as the number of collectors increases, the upward wind pressure coefficient of the upper edge become higher than the downward wind pressure coefficient of the lower edge. Finally yet important, it was found that the location of the maximum wind pressure coefficient was changed according to the number of solar collectors.