High-resolution operational coastal modeling for the hydrodynamics in Korea with observed data

Hak-Soo Lim, Chang S. Kim, Kwang-Soon Park, W.-D. Baek, Seonjeong Kim, Se Chul Jang and J.-S. Park

Korea Ocean Research & Development Institute Ansan, Republic of Korea

hslim@kordi.re.kr

Insik Chun Civil Engineering

Konkuk University Seoul, Republic of Korea

ischun@konkuk.ac.kr

Abstract—High-resolution operational oceanographic system has been developing for the coastal waters of Korea using a Regional Ocean Modeling System coupled with wave model SWAN, internally coupled sediment transport model CSTMS and externally nested water quality model CE-QUAL-ICM. The hydrodynamic variables such as sea surface elevation, currents, temperature, salinity, storm surge height, and wave information are predicted twice a day in the 72 hours base. The coastal information system which is based on web-GIS system provides the predicted results with real-time monitoring data for dissemination to the public and validation of the operational model using various visualization techniques. The surface forcing for the operation model ROMS and SWAN is derived from the predicted results of the operational meteorological model WRF or UM which forecasts atmospheric data for the East China Sea and the East Sea. The open boundary condition for the down-scaled ROMS is nested with the predicted results derived from another operational model ROMS for the Yellow Sea or global operational hybrid ocean model HYCOM which forecasts ocean circulation with data assimilation. The previous results simulated 12 hours before are used as an initial condition for the operational oceanographic system. The hydrodynamic results have been calibrated with tidal surface elevation and verified with currents observed by bottom mounted acoustic current meter ADCP or AWAC data in the coastal waters of Korea. For the validation of predicted results we use real-time monitoring data such as hydrodynamic observation monitored by remote Buoy system and ocean observatory tower and 1 hour averaged surface currents derived from HF-Radar system. The suspended solid concentration image retrieved by Geostationary Ocean Color Imager of the satellite COMS will be used for the validation of the model prediction on the suspended sediment transport for the coastal waters of Korea. This high-resolution coastal operational forecasting system will be used as a part of the development of Korea Operational Oceanographic System with other operational oceanographic system.

Keywords-operational oceanographic system; coastal waters; ROMS; acoustic current meter; satellite image

Introduction

Korea Operational Oceanographic System (KOOS) which is supported by the Ministry of Land, Transport and Maritime Affairs (MLTM), Korea has been developing since August, 2009 to support ocean activity and to solve various problems of coastal waters of Korea. The goal of the project is to provide

predicted information to the government agency and to the public to solve pending problems such as oil spill accident, search and rescue (SAR), red tide, wave overtopping, inundation etc. around coast of Korea. As a part of Korea operational operation system (KOOS), we have developed down-scaled operational oceanographic system using the Regional Ocean Modeling System (ROMS) for the coastal hydrodynamics in Korea. The coastal operational oceanographic system which has fine grid system covering western and southern coastal waters of Korea predicts tides, wind-driven circulation, temperature and salinity etc. twice a day in the 72 hours base. The predicted results are exported to the web-GIS based coastal information system which is based on the Arc-GIS engine for the real-time dissemination to the public.

I. THE MODEL ROMS The ocean circulation model ROMS which has various

computational pathway such as standalone or coupled to atmospheric or wave models is three-dimensional, free-surface, terrain-following numerical model that solves the Reynolds-averaged Navier-Stokes equations using the hydrostatic and Boussinesq assumption developed as a community model by the Rutgers University USA [1]. The model uses a horizontal curvilinear grid system and stretched terrain-following coordinate in vertical array. It has been widely used for a prediction of hydrodynamic variables as well as sediment transport study with highly resolving tidal flat dynamics [2][3][4]. Wave coupled model ROMS enhances the current related bottom stress due to the wave induced oscillatory boundary layer, and wave friction is also increased due to the currents [5]. Being module-based model system, the ROMS is to be operational with easy link or coupling with other models such as WRF for meteorological surface forcing, SWAN for waves, sediment transport, CE-QUAL-ICM coupled externally for water quality, and even with nonlinear processes [6][7].

II. OPERATIONAL OCEANOGRAPHIC SYSTEM The down-scaled operational oceanographic modeling

system for the coastal waters of Korea uses four different domains with cell size of 1.8 km; two domains are for western coastal waters covering 124.0 – 127.0°E, 34.6 – 38.4°N, and other two domains are for southern coastal waters covering

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125.0 – 130.5°E, 32.8 – 35.8°N. Each domain has nested into high-resolution model system to resolve high-resolution hydrodynamics of coastal waters for Incheon port in northwestern coast, Saemangeum estuary in southwestern coast, and southern ports of Yeosu, Masan, and Busan of Korea. In vertical array, we use 20 levels with significant stretching near the surface and bottom to resolve surface suspended transport and bottom sediment transport. For the tides at open boundary, we use major 8 tidal constituents with semi-diurnal tidal constituents (M2, S2, N2, K2) and diurnal tidal constituents (K1, O1, P1, Q1) derived from the regional ocean tide model NAO.99jb with 5′resolution [8]. The initial condition of the model is computed with 2 years simulation using monthly mean temperature and salinity data derived from the World Ocean Atlas 2005 (WOA2005) with monthly mean surface forcing derived from the Comprehensive Ocean-Atmosphere Data Set (COADS). The model is driven on open boundary condition by the predicted results (05:00 and 17:00 Local Standard Time) of another circulation model ROMS with 9 km grid size, in which it has been in operation using data assimilation method for the Yellow Sea providing wind-driven circulation, temperature and salinity. Surface forcing such as wind stress, heat flux and water flux is derived from operational atmospheric model WRF with 4km grid for the East China Sea, in which the predicted result is automatically converted into for the operational model. For restarting the operational system, the model uses the previous result simulated 12 hours before as an initial condition. With the predicted atmospheric surface forcing and nested open boundary condition automatically converted through shell-script, the operational model forecasts tides, wind-driven currents, temperature, salinity, storm surge height, and wave information twice a day (06:00 and 18:00) for 72 hours. Figure 1 shows process of down-scaled high-resolution operational oceanographic system for the coastal waters of Korea using wave coupled model ROMS.

III. OPERATION OF THE SYSTEM The high-resolution operational oceanography system

comprises of atmospheric and hydrodynamic models coupled with 3-D hydrodynamics, wave, sediment transport and water quality modules. The operational model predicts tides, wind-driven circulation, temperature and salinity twice a day in the 72-hours base. The predicted results are exported to the web-GIS system for real-time dissemination to the public and validation with real-time monitoring data. For the validation of the operational model, real-time monitoring data from Buoy, ocean observatory tower and HF-Radar system near the coastal area is integrated through web-GIS based coastal information network system which provides real-time visualization and analysis tools for comparison of predicted result and observed data. The operational model ROMS uses nested boundary condition from Yellow Sea operational model and surface forcing obtained twice a day (05:00 and 17:00 Local Standard Time) from the operational WRF model simulated by KORDI. The boundary and atmospheric data derived from the operational ocean and atmospheric models are automatically converted into boundary condition and atmospheric forcing for the operational regional ROMS for the coastal waters of Korea.

Then, the model uses previous result simulated at 12 hours before as an initial condition to restart model and forecasts tides, wind-driven currents, temperature and salinity twice a day (06:00 and 18:00) in 72 hour base.

Figure 1. Process of operational oceanographic system for the coastal waters of Korea

IV. CONCLUSION We have been developing a down-scaled high-resolution

operational oceanographic system for the coastal waters of Korea. The operational oceanographic system consists of atmospheric and hydrodynamic models coupled with three-dimensional hydrodynamics, wave, sediment transport and water quality modules. We predict hydrodynamic variables of coastal waters twice a day in the 72-hours base including sea surface elevation, currents, temperature, salinity, and waves etc. The predicted results are exported to the web-GIS based coastal information system for the real-time dissemination to the public using visualization technique.

The operational coastal modeling system uses ocean model ROMS coupled with a wave model SWAN for the hydrodynamics and waves, a meteorological model WRF for the atmospheric surface forcing, a regional tide model NAO.99jb for the tides, and a eutrophication model CE-QUAL-ICM for the water quality. The surface forcing for the operational model is derived from the predicted results of the atmospheric model WRF which has been forecasted for the East China Sea. The open boundary condition is nested with the predicted results of another wave coupled operational model ROMS which has been in operation for the Yellow Sea with 9 km resolution. For the restart of the operational system, the model uses the previous results simulated 12 hours before as an initial condition.

The hydrodynamic model ROMS has been calibrated with tidal surface elevation and verified with current data observed by bottom mounted ADCP and AWAC near the coastal waters of Korea. To validate the operational model we use real-time monitoring data such as hydrodynamic observations by remote Buoy System, 1 hour averaged surface currents observed by HF-Radar System, surface sediment concentration derived from geostationary ocean color image (GOCI), and ocean

hydrodynamic data observed by the IEODO tower which is located about 150 km southwest of Jeju island on the south coast of Korea. In this study, we have developed an operational oceanographic system for the hydrodynamics in Korea using wave coupled operational model ROMS. This system will support the operation of KOOS system providing predicted results for the coastal waters including hydrodynamics and wave information twice a day for 72 hours. The predicted results are represented through web-GIS coastal information system visualizing geo-referenced variables more effectively and validating with real-time monitoring data.

ACKNOWLEDGMENT This research was a part of the project entitled

“Development of Korea Operational Oceanographic System (PM56611)” and “functional improvement of Korea Ocean Satellite Center (PE98781)” funded by Ministry of Land, Transport and Maritime Affairs, Korea. Partial supports by In-House Project on “Accuracy Improvement of Spatial Current Vector using Multi sensor Satellite Observation (PE98721)” funded by Korea Ocean Research & Development Institute are greatly appreciated.

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