Quantitative forecast experiment of a heavy rainfall event over Korea in a global model: horizontal resolution versus lead time issues

In this study, we examine the deterministic predictability of heavy rainfall over the Korean peninsula using a global model, the Global/Regional Integrated Model system, by focusing on the effects of horizontal resolution and lead time prior to the onset of the target event. The control run reproduces locally concentrated heavy rainfall over the mid-western part of the Korean peninsula on 27–29 July 2011, with a model setup of about 25 km grid spacing and 24 h in advance of the onset of heavy rainfall. We found that small-scale features are represented well at higher resolution, but without significant change in the distribution of rainfall. Increase of lead time reduces the predictability of large-scale features, accompanying a northward shift of major rainfall. At lower resolution, the accuracy of the heavy rainfall prediction decreases more rapidly as lead time increases. We concluded that the increase in predictability of heavy rainfall achieved by enhancing horizontal resolution is promising, but an additional set of experiments also indicates that efforts should be made to improve the physics packages in models.     

A numerical study on severe downslope windstorms occurred on 5 April 2005 at Gangneung and Yangyang, Korea

Severe downslope windstorms occurred on 5 April 2005 in the Taebaek Mountain Range, located in the eastern coast of Korea, are examined using the Weather Research and Forecasting (WRF) model. Strong winds are observed at Gangneung and Yangyang during two separate periods with a rapidly decreasing period in between. These downslope windstorms are reproduced in the simulation reasonably well, although the rapidly decreasing surface wind speed after the second windstorm could not be captured at Yangyang. It is found that the generation mechanisms of the downslope windstorms in these two periods are somewhat different. The severe wind in the first period is likely due to the reflection of the mountain waves from a critical level that locates near z = 8–9 km. Upward-propagating waves and reflected downward-propagating waves interact constructively in a duct between the critical level and the surface, resulting in strong surface wind. In the second period, the hydraulic-jump theory can be applied in that the wave breaking above the downstream induces a well-mixed region, and severe downslope wind is developed beneath this turbulent region as the streamlines descend along the downstream. Simultaneous lee wave structure is also reproduced during the second windstorm period. The sensitivity of the downslope wind speed to the change in the land-cover map showed that the absorption of trapped lee waves in the boundary layer reduces the downslope wind speed significantly after the second windstorm at Gangneung, improving the model performance, although with no significant impact at Yangyang.     

关于渗流有限单元法因时空离散而产生的误差讨论

应用有限单元法进行地下水模拟及管理,由于把本来连续的时间和空间离散化,因而会造成一定误差,有时这种误差是不容忽视的.通过计算实例,分析了不同的空间、时间离散格式而产生的误差,应用迭加原理及特征值有限单元法,将因空间和时间离散而产生的误差区分开来,并探讨了减小误差的方法.     

滩涂水边线Landsat-5影像提取方法

快速获取遥感影像水边线时空变化信息具有重要意义,滩涂水边线提取一直是遥感技术应用的难点问题。水边线在遥感影像上具有独特的空间关系与光谱特征。本文综合使用颜色模型变换法、信息熵计算法、最大类间方差法及边缘检测方法。以长江口崇明东滩为研究区,研究了Landsat-5卫星影像海陆对比度增强及不同尺度下的边缘提取,重点给出了基于热红外波段的水边线空间特征与光谱特征的计算方法,在面向对象技术框架下提出了一种顾及空间关系和光谱特征的遥感影像水边线快速提取方法。实验结果表明:(1)基于最大类间方差法的局部阈值分割法能够自动提取band 6的水边线,水边线连续、完整,空间信息丰富;(2)综合使用最佳指数法、离散度方法及颜色模型变换方法,能够有效增强海陆对比度,基于最大类间方差法的局部自适应Canny算子能够自动检测出增强后遥感影像高精度边缘;(3)利用水边线的空间关系和光谱特征,能够由计算机自动实现水边线的识别与连接工作;(4)本文提出的水边线提取方法速度快、自动化程度高,分别继承了阈值分割法的连续性强的优点和Canny算子定位精度高、细节呈现能力强的优势。研究结果对于海岸带动态变化、陆海相互作用机制、海岸带资源保护与开发及近海工程管理等研究具有重要的参考价值。     

Impacts of marine debris on wild animals in the coastal area of Korea

Over the last decade, marine debris has become a major factor affecting the coastal ecosystem of Korea. This study compiled information regarding how marine debris impacts wildlife in Korea. Cases of marine debris impacting wildlife were collected from experts of various fields and from local participants through an open access website from February 2010 to March 2012. A total of 21 species were affected by marine debris: 18 species of birds, 2 species of mammals, and 1 species of crustacean. Five threatened or protected species were identified: black-faced spoonbill, finless porpoise, water deer, whooper swan, and greater painted snipe. Recreational fishing gears were the types of debris that most frequently impacted wildlife, especially birds. Black tailed gulls were the most vulnerable species to recreational fishing hooks and lines. Although it was preliminary, this study revealed that recreational fishing activities should be prioritized when managing marine debris in Korea.     

Three-dimensional visualization of an emotional map with geographical information systems: a case study of historical and cultural heritage in the Yeongsan River Basin,Korea

The objective of this study is the production and visualization of an emotional map to reveal the unique emotions inherent to the areas surrounding the Yeongsan River, which is often referred to as ‘the cradle of civilization’ in Korea. The sites selected for this study are the 11 cities and districts (5667.6 km²) that cut across the vast granary in the southeastern region of Korea, near the Yeongsan River. The emotional map was produced by extracting features of historical and cultural heritage distributed throughout this region and by using a geographic information systems program and its functions for spatial analysis. A database was constructed through interviews with locals and Global Positioning System to index 4318 pieces of cultural heritage to achieve the visualization of emotions. Among the 558 historical relics considered for representing the regional culture, 100 with the largest emotional impact were selected. It was determined that loyalty (), justice (), courtesy (), resentment (), and anger () should be the major emotional elements. Methodologically, a set of regional, periodic, historical, and emotional classification codes were first systematized. After subjecting this data to inverse distance weight interpolation and vertical exaggeration coefficients, the three-dimensional emotional map could be visualized.     

Geotechnical characterization of marine sediments in the Ulleung Basin,East Sea

The geotechnical characteristics of Ulleung Basin sediments are explored using depressurized samples obtained at 2100 m water depth and 110 m below the sea floor. Geotechnical index tests, X-ray diffraction, and SEM images were obtained to identify the governing sediment parameters, chemical composition and mineralogy. We use an instrumented multi-sensor oedometer cell to determine the small-strain stiffness, zero-lateral strain compressibility and electromagnetic properties, and a triaxial device to measure shear strength. SEM images show a sediment structure dominated by microfossils, with some clay minerals that include kaolinite, illite, and chlorite. The preponderant presence of microfossils determines the high porosity of these sediments, defines their microstructure, and governs all macroscale properties. The shear wave velocity increases as the vertical effective stress increases; on the other hand, porosity, permittivity, electrical conductivity, and hydraulic conductivity decrease with increasing confinement. All these parameters exhibit a bi-linear response with effective vertical stress due to the crushable nature of microfossils. Well-established empirical correlations used to evaluate engineering parameters do not apply for these diatomaceous sediments which exhibit higher compressibility than anticipated based on correlations with index properties. Settlements will be particularly important if gas production is attempted using depressurization because this approach will cause both hydrate dissociation and increase in effective stress.     

Sources of plastic marine debris on beaches of Korea: More from the ocean than the land

Reduction of marine debris requires knowledge of its sources. Sources of plastic marine debris found on six beaches of Korea were estimated. Samples larger than 25 mm were collected from 10 quadrats of 5 × 5 m for each beach in spring 2013. The total 752 items (12,255 g) of debris comprised fiber and fabric (415 items, 6,909 g), hard plastic (120 items, 4,316 g), styrofoam (93 items, 306 g), film (83 items, 464 g), foamed plastic other than styrofoam (21 items, 56 g), and other polymer (20 items, 204 g). With the probable sources allocated to each of 55 debris types, the source of 56% of all the collected debris appeared to be oceanbased and 44% was land-based. Priorities of policy measures to reduce marine debris should be different from regions to regions as the main sources of debris may differ.     

Determination of Joint Roughness Coefficients Using Roughness Parameters

This study used precisely digitized standard roughness profiles to determine roughness parameters such as statistical and 2D discontinuity roughness, and fractal dimensions. Our methods were based on the relationship between the joint roughness coefficient (JRC) values and roughness parameters calculated using power law equations. Statistical and 2D roughness parameters, and fractal dimensions correlated well with JRC values, and had correlation coefficients of over 0.96. However, all of these relationships have a 4th profile (JRC 6–8) that deviates by more than ±5 % from the JRC values given in the standard roughness profiles. This indicates that this profile is statistically different than the others. We suggest that fractal dimensions should be measured within the entire range of the divider, instead of merely measuring values within a suitable range. Normalized intercept values also correlated with the JRC values, similarly to the fractal dimension values discussed above. The root mean square first derivative values, roughness profile indexes, 2D roughness parameter, and fractal dimension values decreased as the sampling interval increased. However, the structure function values increased very rapidly with increasing sampling intervals. This indicates that the roughness parameters are not independent of the sampling interval, and that the different relationships between the JRC values and these roughness parameters are dependent on the sampling interval.