Wave-tide-surge coupled model simulation for Typhoon Maemi

1 IntroductionThe main reason for coupling the tide and surgehydrodynamic model with a surface wave model canbe found in the physical interactions taking place inthe surface and bottom boundary layers. During thesevere storm conditions such interactions a…     

Design and implementation of time efficient trajectories for autonomous underwater vehicles

This paper discusses control strategies adapted for practical implementation and efficient motion of autonomous underwater vehicles (AUVs). For AUVs we would like efficiency in both the measured time and the energy consumption, the mission dictating the weight to put on each of these cost. As a first approach to this problem, we focus in this paper on time minimization. Based on the structure of the time optimal trajectories and of the pure motions, we develop an algorithm to design time efficient trajectories corresponding to piecewise constant thrust arcs with few actuator switchings. We do that by solving a new optimization problem where the unknowns are the time period between two actuator switchings as well as the values of the constant thrust arcs. We apply a direct method to compute the solutions numerically. With our algorithm, we gain considerable computational time. Moreover, with as few as three actuator switchings, the duration of our trajectories is within 10% of the optimal trajectories. Since our control strategies have a simple structure they can be implemented on a test-bed vehicle. For the experiments displayed in this paper we use a spherical underwater vehicle which exhibits with almost no preference of direction or orientation for movement; this gives us a very controllable and versatile vehicle.     

Seasonal variation in the community and size structure of nano- and microzooplankton in Gyeonggi Bay,Yellow Sea

To investigate the seasonal variation and community structure of nano- and microzooplankton in Gyeonggi Bay of the Yellow Sea, the abundance and carbon biomass of nano- and microzooplankton were evaluated at 10-day intervals from January 1997 to December 1999. Four major groups of nano- and microzooplankton communities were classified: heterotrophic ciliates, heterotrophic dinoflagellates (HDF), heterotrophic nanoflagellates (HNF), and copepod nauplii. The total carbon biomass of nano- and microzooplankton ranged from 10.2 to 168.8 μg C L⁻¹ and was highest during or after phytoplankton blooms. Nano- and microzooplankton communities were composed of heterotrophic ciliates (7.4–81.4%; average 41.7% of total biomass), HDF (0.1–70.3%; average 26.1% of total biomass), copepod nauplii (1.6–70.6%; average 20.7% of total biomass), and HNF (0.8–59.5%; average 11.5% of total biomass). The relative contribution of individual components in the nano- and microzooplankton communities appeared to differ by seasons. Ciliates accounted for the most major component of nano- and microzooplankton communities, except during summer and phytoplankton blooming seasons, whereas HDF were more dominant during the phytoplankton blooming seasons. The abundance and biomass of nano- and microzooplankton generally followed the seasonal dynamics of phytoplankton. The size and community distribution of nano- and microzooplankton was positively correlated with size-fractionated phytoplankton. The carbon requirement of microzooplankton ranged from 60 to 83% of daily primary production, and was relatively high when phytoplankton biomass was high. Therefore, our result suggests that the seasonal variation in the community and size composition of nano- and microzooplankton appears to be primarily governed by phytoplankton size and concentration as a food source, and their abundance may greatly affect trophic dynamics by controlling the seasonal abundance of phytoplankton.     

Distribution pattern of zooplankton in the han river estuary with respect to tidal cycle

The monthly distribution of zooplankton communities in Han River estuary was investigated at two stations from July 1998 to June 1999. Monthly mean abundance of total zooplankton varied remarkably, with the range from 20 indiv.·m^-3 to 19,600 indiv.·m^-3. During the study period, dominant species of zooplankton community were dinoflagellateNoctiluca scintillans, copepodsParacalanus indicus, Paracaanus crassirostris, Acartia hongi, Acartia ohtsukai, and meroplanton cirriped larvae. According to tidal states, relative high abundance occurred at high tide without regard to season. The temporal distribution of abundance implied that the reduced salinity probably limited the zooplankton populations and the fluctuations of salinity were an important factor in the variation of abundance. However, the results of salinity tolerance test shows that the variations in salinity do not directly influence the decrease of abundance. This study shows that the relatively high abundance of zooplankton near high tide seems to be related with the expansion of abundant zooplankton inhabiting Incheon coastal waters through tidal currents.     

The origin and evolution of mineralizing fluids in the Cretaceous Gyeongsang Basin, Southeastern Korea

Ferroalloy, base-metal and precious-metal deposits in or around the Gyeongsang Basin, which is located in the Cretaceous volcano-sedimentary terrain at the southeastern Korea, displays a genetic relationship with subvolcanic activities of Late Cretaceous to Tertiary age. Diverse mineralization, which occurs as vein, breccia-pipe, porphyry-style and skarn deposits, took place from 108 to 45 Ma that overlapped with polyphase episodes of igneous activity. Based on the mineralogy, host rock, fluid inclusion and stable isotope data of the deposits, the systematic variation of physicochemical conditions is thought to be due to their relative positions with respect to a magma source that is genetically related to a low to intermediate-sulfidation porphyry system. There appears to be a systematic decrease towards δ¹⁸O_H2O values from copper (-gold) and ferroalloy deposits through polymetallic to precious-metal ones. However, Cu (-Au) or Fe–Mo–W deposits are proximal to a magmatic source, whereas polymetallic or precious-metal deposits are more distal to transitional.     

Comparison of groundwater age models for assessing nitrate loading,transport pathways,and management options in a complex aquifer system

In an aquifer system with complex hydrogeology, mixing of groundwater with different ages could occur associated with various flow pathways. In this study, we applied different groundwater age‐estimation techniques (lumped parameter model and numerical model) to characterize groundwater age distributions and the major pathways of nitrate contamination in the Gosan agricultural field, Jeju Island. According to the lumped parameter model, groundwater age in the study area could be explained by the binary mixing of the young groundwater (4–33 years) and the old water component (>60 years). The complex hydrogeologic regimes and local heterogeneity observed in the study area (multilayered aquifer, well leakage hydraulics) were particularly well reflected in the numerical model. The numerical model predicted that the regional aquifer of Gosan responded to the fertilizer applications more rapidly (mean age: 9.7–22.3 years) than as estimated by other models. Our study results demonstrated that application and comparison of multiple age‐estimation methods can be useful to understand better the flow regimes and the mixing characteristics of groundwater with different ages (pathways), and accordingly, to reduce the risk of improper groundwater management plans arising from the aquifer heterogeneity.     

Unexpected nationwide nitrate declines in groundwater of Korea

Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen fertilizer to croplands is one of the major sources of high nitrate content in groundwater. In this study, we analyse the nitrate concentrations in Korean groundwater based on data from groundwater quality monitoring wells (n = 1,022–2,072), which were sampled twice annually over a recent 13‐year analysis period (2001–2013). We report that groundwater nitrate levels are decreasing, despite steadily increasing groundwater use. The maximum nitrate concentration decreased from 168.91 to 48.11 mg/L, whereas the mean values also show a gradual decreasing trend. Non‐parametric Mann–Kendall tests on nitrate concentrations also confirm the decreasing trend. The nitrate decrease is more clearly evident in agricultural groundwater as compared to domestic and drinking groundwaters. This decrease of nitrate in groundwater coincides with a large decline in nitrogen fertilizer application due to reduced cropland areas, more sustainable agricultural practices, and progressive improvement of sewage disposal services. This study proposes that the long‐term adoption of best practices in agriculture has had a positive impact on groundwater nitrate control.     

Geospatial blending to improve spatial mapping of precipitation with high spatial resolution by merging satellite‐based and ground‐based data

Estimating accurate spatial distribution of precipitation is important for understanding the hydrologic cycle and various hydro‐environmental applications. Satellite‐based precipitation data have been widely used to measure the spatial distribution of precipitation over large extents, but an improvement in accuracy is still needed. In this study, three different merging techniques (Conditional Merging, Geographical Differential Analysis and Geographical Ratio Analysis) were used to merge precipitation estimations from Communication, Ocean and Meteorological Satellite (COMS) Rainfall Intensity data and ground‐based measurements. Merged products were evaluated with varying rain‐gauge network densities and accumulation times. The results confirmed that accuracy of detecting quantitative rainfall was improved as the accumulation time and network density increased. Also, the impact of spatial heterogeneity of precipitation on the merged estimates was investigated. Our merging techniques reproduced accurate spatial distribution of rainfall by adopting the advantages of both gauge and COMS estimates. The efficacy of the merging techniques was particularly pronounced when the spatial heterogeneity of hourly rainfall, quantified by variance of rainfall, was greater than 10 mm²/accumulation time². Among the techniques analysed, Conditional Merging performed the best, especially when the gauge density was low. This study demonstrates the utility of the COMS Rainfall Intensity product, which has a shorter latency time (1 h) and higher spatio‐temporal resolution (hourly, 4 km by 4 km) than other widely used satellite precipitation products in estimating precipitation using merging techniques with ground‐based point measurements. The outcome has important implications for various hydrologic modelling approaches, especially for producing near real‐time products. Copyright © 2016 John Wiley & Sons, Ltd.