• 천문학회보
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• 제43권2호
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• pp.45.2-45.2
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• 2018

Twisted magnetic flux tubes (also called magnetic flux ropes) are believed to play a crucial role in solar eruptive phenomena. The evolution of a single flux rope with or without the influence of an overlying field of a simple geometry has been extensively studied and its physics is rather well understood. Observations show that interacting flux tubes are often involved in solar eruptions. It was Lau and Finn (1996) who intensively studied the interaction between two flux ropes, whose footpoints are anchored in two parallel planes. In this too simplified setting, the curvature of the flux rope axial fields is totally ignored. In our study, the footpoints of flux ropes are placed in a single plane containing a polarity inversion line as in the real solar active region. Our simulation study is performed for four cases: (1) co-axial field and co-axial current (co-helicity), (2) counter-axial field and co-axial current (counter-helicity), (3) co-axial field and counter-axial current (counter-helicity), and (4) counter-axial field and counter-axial current (co-helicity). Except case 3, each case is found to be related with certain eruptive features.

• 한국농공학회논문집
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• 제57권3호
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• pp.109-120
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• 2015

Spatial heterogeneous characteristics of solar radiation energy from Climate Change gives rise to energy imbalance in the general ecological system including water resources. This study is to estimate the $CO_2$ flux of South Korea using Terra MODIS image and to assess the reliability of MODIS data from the ground measured $CO_2$ flux by eddy covariance flux tower data at 3 locations (two at mixed forest area and one at rice paddy area). The MODIS Gross Primary Productivity (GPP) product (MOD17A2), 8-day composite at 1-km spatial resolution was adopted for the spatial $CO_2$ flux generation. The MOD17A2 data by noise like cloud and snow in a day were tried to fill by Inverse Distance Weighted (IDW) method from valid pixels and the damping effect of MOD17A2 data were corrected by Quality Control (QC) flag. The MODIS $CO_2$ flux was estimated as the sum of GPP and Re (ecosystem respiration) by Lloyd and Taylor method (1994). The determination coefficient ($R^2$) between MODIS $CO_2$ and flux tower $CO_2$ for 3 years (2011~2013) showed 0.55 and 0.60 in 2 mixed forests and 0.56 in rice paddy respectively. The $CO_2$ flux generally fluctuated showing minus values during summer rainy season (from July to August) and maintaining plus values for other periods. The MODIS $CO_2$ flux can be a useful information for extensive area, for example, as a reliable indicator on ecological circulation system.

• 한국농림기상학회지
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• 제5권2호
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• pp.94-100
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• 2003

토양으로부터의 $CO_2$ 방출은 생태계의 탄소 순환에 중요한 위치를 차지한다. 주요 생태계의 순 $CO_2$ 교환과 일차 생산량 등을 정확히 산출하려면 군락 $CO_2$ 플럭스와 더불어 토양 $CO_2$ 플럭스의 관측이 함께 이루어져야 한다. 본 논문에서는 닫힌 역학 챔버 시스템을 활용한 토양 이산화탄소 플럭스의 관측 방법을 간략히 검토하고, 한반도 주요 생태계에 구축된 한국 타워 플럭스 관측 지역망(KoFlux)의 거점 관측소에서 예비 관측된 결과와 서로 다른 관측 시스템간의 상호비교 결과를 보고하고자 한다.

• 한국습지학회지
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• 제17권3호
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• pp.283-292
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• 2015

토양으로부터 방출되는 $CO_2$의 양은 전 지구적 지구 탄소 순환에서 가장 큰 방출 중 하나로 알려져 있다. 특히 토양 내 미생물의 유기물질 분해 과정에 의해 방출되는 이산화탄소의 양은 토양의 탄소 저장량을 장기적으로 결정하는 요인이 되므로 그 양을 정량화 하는 것이 필요하다. 본 연구는 토양에서 고라니의 분변이 $CO_2$ 배출에 미치는 영향을 파악하기 위해 수행하였다. 그리고 고라니의 분변이 토양의 $CO_2$ 배출에 주는 영향과 토지의 이용에 따라 변화하는 $CO_2$ flux를 정량화 하였다. 그 결과 고라니 분변 내 많은 유기물질은 토양 미생물의 활성화에 영향을 주고 그로 인해 토양의 호흡 및 토양 내 물리 화학적인 변화가 발생되어 토양의 유기물 함량이 서로 다르게 나타남을 확인할 수 있었다. 특히 4개 지역의 토양(경작지, 휴경지, 버드나무 군락, 갈대습지)의 C/N ratio와 $CO_2$ flux는 분변의 유무와 통계적으로 매우 유의미한 상관 관계를 나타냈으며(P<0.01), 분변의 영향을 받은 토양의 $CO_2$ flux는 분변의 영향을 받지 않은 토양보다 2-20배 더 높은 것으로 나타났다. 이 연구는 고라니의 분변이 토양에 주는 영향과 야생동물 분변을 이용한 토양 물질 순환 연구를 통해 육상 생태계 및 토양권의 물질 순환과 그 영향의 정도를 정량화 하였다는 점에서 큰 의의가 있는 연구이다.

• Ocean and Polar Research
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• 제26권2호
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• pp.145-154
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• 2004

Surface energy and $CO_2$ fluxes have been measured over an ocean at Ieodo Ocean Research Station of KORDI since May 2003. Eddy covariance technique, which is a direct flux measurement, is used to quantitatively understand the interaction between the ocean surface and the atmospheric boundary layer. Although fluxes were continuously measured during the period from May 2003 to February 2004, the quality control of these data yielded <20% of data retrieval. The atmospheric stability did not show any distinct dirunal patterns and remained near-neutral to stable from May to June but mostly unstable during fall and winter in 2003. Sensible heat flux showed a good correlation with the difference between the sea water temperature and the air temperature. The maximum fluxes of sensible heat and latent heat were $120Wm^{-2}$ and $350Wm^{-2}$ respectively, with an averaged Bowen ratio of 0.2. The ocean around the tower absorbed $CO_2$ from the atmosphere and the uptake rates showed seasonal variations. Based our preliminary results, the daytime $CO_2$ flux was steady with an average of $-0.1 mgCO_2m^{-2}s^{-1}$ in summer and increased in winter. The nighttime $CO_2$ uptake was greater and fluctuating, reaching up to $-0.1 mgCO_2m^{-2}s^{-1}$ but these data require further examination due to weak turbulent mixing at nighttime. The magnitude of $CO_2$ flux was positively correlated with the half hourly changes in horizontal mean wind speed. Due to the paucity of quality data, further data collection is needed for more detailed analyses and interpretation.

• 한국농림기상학회지
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• 제5권2호
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• pp.51-60
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• 2003

한국 내 농경지의 약 60%를 차지하고 있는 논은 아시아의 주요 농업 생태계의 하나이다. 논은 대기로부터 $CO_2$를 흡수함과 동시에 CH$_4$의 형태로 탄소를 대기 중으로 방출하는데, 관개 상태에 따라 흡수와 방출의 상대적 크기가 달라져서 온실 기체의 전구 수지에 중요한 변수로 작용할 수 있다. 온실 효과와 관련하여 논의 현재 및 미래의 역할을 보다 잘 이해하기 위하여, 주요 농업 생태계에서의 $CO_2$와 에너지 교환을 정량화 하는 것은 매우 중요하다. 이 연구의 목적은, 벼의 전체 생장 기간동안 한국의 전형적인 논에서의 에너지와 $CO_2$ 교환과정을 관측, 분석하고 이해하는 것이다. 2002년 4월부터 한국 타워 플럭스 관측 지역망(KoFlux)에속한 강화도 하리의 논에서 $CO_2$ 및 에너지 플럭스 관측을 지속적으로 해오고 있다. 다양한 보정 단계와 처리 과정을 거친 관측 자료를 통해, 논과 대기간의 $CO_2$ 교환량을 정량화하고, 이를 미기상학적, 생물리학적 관점에서 분석하였다. 날씨 변화와 더불어, 지표 피복 변화와 식물의 생장 단계에 따라 $CO_2$ 교환량이 민감하게 변화하였다. 국내 논에서의 전 생장기간에 걸친 에너지와 $CO_2$ 교환에 관한 최초의 직접 관측 보고인 본 연구는, 아시아 플럭스망(AsiaFlux) 내에서 중요한 참고 자료로서의 가치를 지니며, 지면 모형의 보정과 개선, 전구 생지화학적 순환에 대한 논의 역할, 그리고 생물-대기 상호 작용에 대한 근본적인 이해를 향상시키는 데 기여할 것이다.

• 한국대기환경학회지
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• 제28권5호
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• pp.485-494
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• 2012

The purpose of this study is to monitor the flux of $CO_2$ and BVOCs (biogenic volatile organic compounds) between the atmosphere and forest. The main research activities are conducted at Taehwa Research Forest (TRF), managed by the College of Agriculture and Life Sciences at Seoul National University. The TRF site is located 60 km north-east from the center of Seoul Metropolitan Area. The TRF flux tower is in the middle of a Korean Pine (Pinus Koraiensis) plantation ($400m{\times}400m$), surrounded by a mixed forest. Eddy covariance method was used for $CO_2$ flux above the forest and REA (Relaxed eddy accumulation) method applying eddy covariance was used for BVOCs flux. BVOCs flux that was measured in spring (from May 16 to 18) had distribution of 84 to $2917{\mu}g/m^2{\cdot}h$. Especially, it showed that d-limonene being strong reactivity composed the largest fraction of monoterpene. Ambient $CO_2$ concentration measured in Mt. Taehwa was 399 ppm and observed $CO_2$ fluxes between the atmosphere and forest suggested that during the day, $CO_2$ is absorbed by plants through photosynthesis and released during the night.

• Journal of Welding and Joining
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• 제3권1호
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• pp.40-45
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• 1985

Wire meling characteristics were examined with variation of gas formers such as $MgCO_3, CaCO_3 and Li_ 2CO_ 3$ by self-shielded flux cored arc welding. The flux cored wire of overlap type was welded by DCRP. The results obtainedareas follows. 1) Drop type was observed with no gas former, repelled type with MgCO_3$ added and short circuit type with $Li_2CO_3$ added. The variation of transfer mode was related to the blowing force of $CO_2$ gas and the surface tension of the slag. 2) Droplet size increased with adding gas formers due to the effect of $CO_2$ gas cushion. 3) Core spikes were observed more frequently with increasing the amount of gas formers.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.261-266
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• 2003

An experimental study has been conducted to evaluate the effects of $CO_{2}$ on heat transfer from hydrogen oxygen-enriched flame. Experiments were performed on flames stabilized by a co-flow swirl burner, which mounted on top of the furnace. Five composition conditions of oxidizer were chosen with replacing $N_{2}$ with $CO_{2}$. In a steady state, total and radiative heat flux rates from the flame to the wall of furnace has been measured using heat flux meters. Temperature distribution in furnace also has been checked. Increasing $CO_{2}$ ratio in the oxidizer, the dominant heat transfer mode was changed into convection from radiation. Temperature in the furnace decreased but total heat flux increased.

• 한국농공학회논문집
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• 제53권2호
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• pp.1-8
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• 2011

In this study, In order to evaluate reliable of MODIS GPP, the MODIS GPP and Flux tower measured GPP were compared to evaluate the use of method on 8 days composite MODIS GPP. The 2008 Flux data ($CO_2$ Flux and air temperature) measured in Seolmacheon watershed ($8.48\;km^2$) were used. The Flux tower GPP was estimated as the sum of $CO_2$ Flux and $R_{ec}$ (ecosystem respiration) by Lloyd and Taylor method (1994). The summer Monsoon period from June to August mostly contributed the underestimation of MODIS GPP by cloud contamination on MODIS pixels. The 2008 MODIS GPP and Flux tower GPP of the watershed were $1133.2\;g/m^2/year$ and $1464.3\;g/m^2/year$ respectively and the determination coefficient ($R^2$) after correction of cloud-originated errors was 0.74 (0.63 before correction). Even though effect of Cloud-Originated Errors was eliminated, Solar radiation and Temperature are affected at GPP. Measurement of correct GPP is difficult. But, If errors of MODIS GPP analyze on Cloud Moonsoon Climate in korea and eliminated effect of Cloud-Originated Errors, MODIS GPP will be considered GPP increasing of 9 %. There, Our results indicate that MODIS GPP show reliable and useful data except for summer period in Moonsoon Climate.