Abstract This is a study of the storm surge trends in some of the typhoon-prone coastal areas of China. An unstructured-grid, storm surge-wave-tide coupled model was established for the coastal areas of Zhejiang, Fujian and Guangdong provinces. The coupled model has a high resolution in coastal areas, and the simulated results compared well with the in situ observations and satellite altimeter data. The typhoon-induced storm surges along the coast of the study areas were simulated based on the established coupled model for the past 20 years (1997–2016). The simulated results were used to analyze the trends of the storm surges in the study area. The extreme storm surge trends along the central coast of Fujian Province reached up to 0.06 m/y, significant at the 90% confidence level. The duration of the storm surges greater than 1.0 and 0.7 m had an increasing trend along the coastal area of northern Fujian Province, significant at confidence levels of 70%–91%. The simulated trends of the extreme storm surges were also validated by observations from two tide gauge stations. Further studies show that the correlation coefficient (RTE) between the duration of the storm surge greater than 1 m and the annual ENSO index can reach as high as 0.62, significant at the 99% confidence level. This occurred in a location where the storm surge trend was not significant. For the areas with significant increasing storm surge trends, RTE was small and not significant. This study identified the storm surge trends for the full complex coastline of the study area. These results are useful both for coastal management by the government and for coastal engineering design.

Study of Storm Surge Trends in Typhoon-prone Coastal Areas Based on Observations And Surge-wave Coupled Simulations

Wave data prediction with optimized machine learning and deep learning techniques

Prediction of significant wave height in hurricane area of the Atlantic Ocean using the Bi-LSTM with attention model

Two Ocean State Monitoring and Analyzing Radar (OSMAR071) (7.8 MHz) high-frequency (HF) radars and four moored ADCPs were operated concurrently in the southwestern Taiwan Strait during January–March 2013. Qualitative and quantitative comparisons of surface currents were conducted between the HF radars and the ADCPs. Except for a location probably affected by shallow water and sand waves on the Taiwan Banks, the HF-radar-derived radial currents (radials) showed good agreement with the ADCP measured results (correlation coefficient: 0.89–0.98; rms difference: 0.07–0.13 m s−1). To provide further insight into the geophysical processes involved, the performance of the HF-radar-derived radials was further evaluated under different sea states (sea states: 2–6). It was found that both the data returns of the radar-derived radials and the differences between the radar-derived radials and the ADCP-derived radials varied with sea state. The HF radar performed best at sea state 4 in terms of data returns. The spatial coverage increased rapidly as the waves increased from sea state 2 to 4. However, it decreased slowly from sea state 4 to 6. Second, the radial differences were relatively high under lower sea states (2 and 3) at the location where the best agreement was obtained between the radar and ADCP radials, whereas the differences increased as the sea states increased at the other three locations. The differences between the radials measured by the HF radars and the ADCPs could be attributed to wave-induced Stokes drift and spatial sampling differences.

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Assessment of HF Radar in Mapping Surface Currents under Different Sea States

Based on the Ocean Projection and Extension neural Network (OPEN) method, a novel approach is proposed to retrieve sea surface wind speed for C-band synthetic aperture radar (SAR). In order to prove the methodology with a robust dataset, five-year normalized radar cross section (NRCS) measurements from the advanced scatterometer (ASCAT), a well-known side-looking radar sensor, are used to train the model. In situ wind data from direct buoy observations, instead of reanalysis wind data or model results, are used as the ground truth in the OPEN model. The model is applied to retrieve sea surface winds from two independent data sets, ASCAT and Sentinel-1 SAR data, and has been well-validated using buoy measurements from the National Oceanic and Atmospheric Administration (NOAA) and China Meteorological Administration (CMA), and the ASCAT coastal wind product. The comparison between the OPEN model and four C-band model (CMOD) versions (CMOD4, CMOD-IFR2, CMOD5.N, and CMOD7) further indicates the good performance of the proposed model for C-band SAR sensors. It is anticipated that the use of high-resolution SAR data together with the new wind speed retrieval method can provide continuous and accurate ocean wind products in the future.

https://www.mdpi.com/2072-4292/14/9/2269/pdf?version=1652149465

A Neural Network Method for Retrieving Sea Surface Wind Speed for C-Band SAR

CRBM-DBN-based prediction effects inter-comparison for significant wave height with different patterns

Dual high-frequency (HF) radar systems are often used to provide measurements of waves, winds, and currents. In this study, the accuracy of wave measurements using a single HF radar system ...

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Assessment of Significant Wave Height in the Taiwan Strait Measured by a Single HF Radar System

Accurate storm surge forecasts provided rapidly could support timely decision-making with consideration of tropical cyclone (TC) forecasting error. This study developed a fast storm surge ensemble prediction method based on TC track probability forecasting and searching optimization of a numerical scenario database (SONSD). In a case study of the Fujian Province coast (China), a storm surge scenario database was established using numerical simulations generated by 93,150 hypothetical TCs. In a GIS-based visualization system, a single surge forecast representing 2562 distinct typhoon tracks and the occurrence probability of overflow of seawalls along the coast could be achieved in 1–2 min. Application to the cases of Typhoon Soudelor (2015) and Typhoon Maria (2018) demonstrated that the proposed method is feasible and effective. Storm surge calculated by SONSD had excellent agreement with numerical model results (i.e., mean MAE/RMSE: 7.1/10.7 cm, correlation coefficient: >0.9). Tide prediction also performed well with MAE/RMSE of 9.7/11.6 cm versus the harmonic tide, and MAE/RMSE of phase prediction for all high waters of 0.25/0.31 h versus observations. The predicted high-water level was satisfactory (MAE of 10.8 cm versus observations) when the forecasted and actual positions of the typhoon were close. When the forecasted typhoon position error was large, the ensemble surge prediction effectively reduced prediction error (i.e., the negative bias of −58.5 cm reduced to −5.2 cm versus observations), which helped avoid missed alert warnings. The proposed method could be applied in other regions to provide rapid and accurate decision-making support for government departments.

/pdf/fast-storm-surge-ensemble-prediction-using-searching-cfeni861ns.pdf

Fast Storm Surge Ensemble Prediction using Searching Optimization of a Numerical Scenario Database

Provided is a method of effectively improving the flow direction measurement precision of an acoustic doppler current profiler (ADCP), relating to an ADCP. The method comprises: firstly, establishing a mathematic model, analyzing the relation between magnetic north angle change and final flow direction change, and obtaining that an angle variable quantity is equal to a flow direction variable quantity when only the magnetic north angle change exists; and based on the above, using a least square method to fit errors of a flow direction influenced by magnetism, and using a fitting coefficient to compensate for ADCP actual measurement flow direction output. Compared with a standard flow direction, the root-mean-square value of the errors of a flow direction influenced by magnetism can be reduced by 70%. The method can effectively compensate for the flow direction error of an ADCP internal magnetic compass caused by environmental magnetic field interference in an azimuth scope of 0-360 DEG, thereby substantially improve flow direction measurement precision in an omnibearing scope, and have engineering guidance value for long-term fixed point flow measurement in sea observation.

Guomei Wei

Papers

CRBM-DBN-based prediction effects inter-comparison for significant wave height with different patterns

Assessment of Significant Wave Height in the Taiwan Strait Measured by a Single HF Radar System

Assessment of HF Radar in Mapping Surface Currents under Different Sea States

Fast Storm Surge Ensemble Prediction using Searching Optimization of a Numerical Scenario Database

Method of effectively improving flow direction measurement precision of acoustic doppler current profiler