• Journal of Korea Water Resources Association
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• v.36 no.3 s.134
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• pp.495-505
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• 2003

Convective weather systems such as organized mesoscale convective systems (Mesoscale Convective Complex, MCC and Convective Cloud Clusters, CCC) and much weaker Disorganized Short-lived Convection (DSC) in the region of India and Nepal were analyzed using the Meteosat-5 IR imagery. The diurnal march and propagation of patterns of convective activity in the Himalayas and Northern Indian subcontinent were examined. Results indicate that infrared satellite images of Northern India and along the southern flank of the Himalayas reveal a strong presence of convective weather systems during the 1999 and 2000 monsoons, especially in the afternoon and during the night. The typical MCCs have life-times of about 11 hours, and areal extent about $300,000km^2$. Although the core of MCC activity remains generally away from the Middle Himalayan range, the occurrence of heavy precipitation events in this region can be directly linked to MCCs that venture into the Lesser Himalayan region and remain within the region bounded by $25^{\circ}-30^{\circ}N$. One principal feature in the spatial organization of convection is the dichotomy between the Tibetan Plateau and the Northern Indian Plains: CCCs and DSCs begin in the Tibetan Plateau in the mid-afternoon into the evening; while they are most active in the mid-night and early morning in the Gangetic Plains and along the southern facing flanks of the Himalayas. Furthermore, these data are consistent with the daily cycle of rainfall documented for a network of 20 hydrometeorological stations in Central Nepal, which show strong nocturnal peaks of intense rainfall consistent with the close presence of Convective Weather Systems (CWSs) in the Gangetic Plains (Barros et al. 2000).

• Journal of the Korean Society for Aviation and Aeronautics
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• v.22 no.2
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• pp.40-47
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• 2014

Heavy Rainfall event accompanying with Mesoscale Convective Systems(MCSs) inducing flash flooding and Muan and Kunsan Airport closing over Jeollabuk-do area was investigated this study. Comparing to previous study(I), this heavy rainfall event was characterized by much abundant moisture from Typhoon, strong conditional convective instability, and cluster type MCSs. It almost impossible to make accurate forecasting of precipitation amounts and life cycle of MCSs unless proper analysis.

• 한국지구과학회:학술대회논문집
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• 2005.02a
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• pp.176-181
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• 2005

한반도에 집중호우를 유발시키는 중규모 대류복합체는 매우 복잡한 특성을 띠고 있다. 2004년 7월14일 발생한 중규모 대류복합체의 발달 메커니즘을 분석한 결과, 대류복합체 생성 전에 500 hPa 고도에서 강한 역전층이 나타났으며, 이 역전층은 상승과 하층간의 상당온위의 분리를 유발하여 대기불안정이 더욱 강화시켰다. 그리고 일반적인 중규모 대류복합체 특징인 풍향의 쉬어 보다는 풍속의 쉬어에 의해 대류계의 열역학 불안정이 강화 되었다.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.129-137
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• 1999

The time of the onset of double-diffusive convection in time-dependent, nonlinear concentration fields is investigated theoretically. The initially quiescent horizontal fluid layer with a uniform temperature gradient experiences a sudden concentration change from below, but its stable thermal stratification affects concentration effects in such way to invoke convective motion. The related stability analysis, including Soret effect, is conducted on the basis of the propagation theory. Under the linear stability theory the concentration penetration depth is used as a length scaling factor, and the similarity transform for the linearized perturbation equations. The newlly obtained stability equations are solved numerically. The resulting critical time to mark the onset of regular cells are obtained as a function of the thermal Rayleigh number, the solute Rayleigh number, and the Soret effect coefficient. For a certain value of the Soret effect coefficient, the stable thermal gradient promote double-diffusive convective motion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1113-1120
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• 2013

A numerical analysis of the effect of the position of a circular cylinder in a $45^{\circ}$ tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between $10^3$ and $10^5$. The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.975-982
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• 2014

This study evaluates the effect of a heated circular cylinder's size on three-dimensional natural convection in a cubical enclosure. The Rayleigh number was varied between $10^3$ and $10^5$, and the Prandtl number was maintained at 0.7. In this study, the radius of the circular cylinder was changed by 0.1 L within a range of 0.1-0.4 L. The thermal and fluid flow characteristics were regarded to be independent of time in the range of the Rayleigh number and cylinder radius considered in this study. The surface-averaged Nusselt numbers of the cylinder and the enclosure were found to increase with the increase in the radius of the cylinder. The effect of the cylinder's size on natural convection in the enclosure was analyzed across the thermal and flow fields, and the distributions of the Nusselt numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.11
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• pp.991-998
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• 2013

A numerical study is carried out for natural convection in an enclosure with an inner hot cylinder at the center. The top wall is cold, the bottom and both side walls of the enclosure are adiabatic, and the cylinder is heated. The bottom wall is heated locally at the middle. The ratio (w) is defined by as the width of the bottom wall to that of the heated local area. The immersed boundary method (IBM) is used to model an inner circular cylinder based on the finite volume method (FVM). This study investigates the effect of w on natural convection in an enclosure with an inner heated cylinder for Rayleigh numbers of $10^6$. At $6Ra=10^6$, thermal and flow fields show time-dependent characteristics after their full development.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.717-726
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• 2016

This study evaluated the effect of aspect ratio of an enclosure with a heated inner circular cylinder on three-dimensional natural convection. The immersed boundary method was used to model the inner circular cylinder based on the finite volume method. The Rayleigh number was varied between $10^5$ and $10^6$, and the Prandtl number was maintained at 0.7. The aspect ratio of the three-dimensional enclosure was changed in steps of 1 within a range of 1-4 by increasing the width of the enclosure. In this study, the flow and thermal fields in the enclosure reached the steady state, and showed a mirror-symmetric pattern with respect to the center plane (x=0). In addition, the surface-averaged Nusselt number of the inner circular cylinder increased, while the total surface-averaged Nusselt number of the enclosure walls decreased with increase in the aspect ratio of the enclosure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.943-950
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• 2014

This paper presents a numerical study conducted for analyzing the effect of the Prandtl number on natural convection in a square enclosure with an inner circular cylinder in various positons. Several Prandtl numbers (Pr = 0.1, 0.7, and 7) and Rayleigh numbers (Ra = $10^3$, $10^4$ and $10^5$) are considered in the numerical study, along with different positions of the inner circular cylinder. The position of the inner circular cylinder is changed in steps of 0.1 in the range of -0.2 to 0.2. The effect of the Prandtl number on natural convection in the enclosure is analyzed on the basis of the thermal and flow fields and the distribution of the Nusselt number. Regardless of the position of the cylinder, when the Rayleigh number is $10^5$, the surface-averaged Nusselt number of the inner cylinder and the enclosure increases as the Prandtl number increases.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2007.05a
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• pp.99-101
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• 2007

비종관 관측자료인 기상위성 및 레이더 분석자료에서 위성영상에서 볼 수 있는 서해남부 해상의 스콜라인 형태의 강한 대류운을 무안-진도 레이더 반사도에 의한 수평 및 연직 구조로 살펴보았는데 특히 발달한 대류운 영역이 보다 상세한 반사도 차이로 나타나고, 40 dBZ 이상 강한 반사도 셀이 고도 6km, 20km 정도의 수평규모를 갖는 여러 대류운시스템이 합쳐진 다중세포시스템으로 구성되어 있음을 알 수 있었다. 또한 연구용 X-대역 무안 레이더 반사도 분포를 보면 사이트 주면에 강한 dBZ의 대류운이 자리하고 있어 발달한 강수입자에 의한 감쇄효과 때문에 북서방향과 남서방향의 강한 대류운들이 약하게 잘못 관측되고 있음을 볼 수 있었지만 S-대역 진도 레이더는 발달한 강수 입자에 크게 영향을 받지 않고 고유의 강한 반사도를 제대로 관측하고 있음을 알 수 있었다. 이와 같이 태풍에 의한 직${\cdot}$간접적인 호우, 장마전선의 활성화에 따른 집중호우를 동반하는 중규모대류운시스템에 대해 정확히 정량적으로 판단할 수는 없지만, 관측자료 분석을 통해 중규모대류운시스템을 발달${\cdot}$유지시킬 수 있는 기구의 존재 가능성을 체계적으로 이해하는데 많은 도움이 되었다. 본 연구 결과를 바탕으로 레이더 반사도와 3차원 바람장 그리고 마이크로강우레이더와 광학강우강계에 의한 연직 구름계와 순간적으로 발생하는 강수특성 등 섬세하고 다양한 비종관 관측자료를 이용하여 집중호우를 유발하는 중규모대류운시스템의 강수 구조와 특성 분석 및 예측에 활용될 수 있으리라 기대된다.