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The purpose of this study is to discuss the influence of signal nonlinearity upon X-band radar observations. A method for estimating the degree of nonlinearity by bispectral analysis was applied and discussed. We found that bispectral analyses from spatial radar backscatter series are similar to results obtained from water level time series. In addition, the average nonlinear degree from radar backscatter is related to wind speed. The accuracy of wave observations derived by consideration of the nonlinear effect from radar backscatter was also investigated. The estimated error in wave height from the radar data is also related to the degree of nonlinearity. In order to improve accuracy, the modulation transfer function method was applied in order to eliminate the influence of nonlinearity.

We here investigate the frequency and intensity of oscillations in oceanographic data within intraseasonal time scales using spectral analysis of surface wind and wave time-series data collected at off-island weather stations or moored buoys around Taiwan. Data from marine weather stations were used to trace atmospheric conditions, while we used buoy data to examine sea states. The spectra and wavelet scalogram of the wind fields revealed oscillations with a period of around 20–33 days, and the energy density of the wind field at the off-island stations was stronger than that at the data buoy stations. However, the wavelet scalogram of the wave height measured at the buoy stations was stronger than its associated wind field. This long-period oscillation is consistent with the wavelet scalogram of the wind field calculated from the off-island weather stations. About 20–33 day oscillations exist within intraseasonal variations, which are closely linked to the atmospheric environment and to wind and ocean wave fields. Oscillations with a period of 5–10 days are a pronounced feature over northeastern Taiwan waters during the winter season and can be interpreted as the wave pattern following synoptic weather systems.

Field oceanographic and meteorological data are required for ocean engineering. In response to the requirement of field data, an operational coastal ocean monitoring network was established around Taiwan coast, including nine deep-water data buoys, one shallow-water pile station, 10 coastal weather stations and 10 tide stations. Data quality check procedures are necessary to ensure the accuracy of measurements. This paper presents the data quality check procedures on ocean wave data which includes automatic and manual check procedures. The checking criteria are derived using statistical theory in this paper. In addition, a sea-state-dependent algorithm is presented in this study in order to derive checking criteria of time-continuity check. It is showed to have better performance of picking up suspicious data than using fixed threshold process. This data quality check program is now used on the operational monitoring network.

This article introduces operational ocean monitoring technologies for the purpose of coastal flooding warning in Taiwan. The in-situ sea state data and field images are linked to the coastal monitoring network of Taiwan. This network provides real-time meteorological and oceanographic information, which is not only for the climate change study but also for the hazard mitigation purposes as well. The whole network has been operated for more than 10 years in Taiwan. It plays an important role on the decision making for the mitigation of coastal flooding.

An operational regional wave forecasting system was established to fulfill the demands of maritime engineering applications on the northeastern coast of Taiwan. This Mixed system consisted of a nested SWAN numerical wave model and experienced marine meteorologists who were sent to the construction site as the in situ predictors to validate output from the numerical model so as to improve the forecasting accuracy.

This study presents a method to use GPS-output velocity signal as wave measurement data. A high pass filter was applied to GPS velocity spectrum in order to separate wave motion and satellite motion in the frequency domain. The vertical displacement spectrum of sea surface particle was obtained from velocity spectrum by applying a transformation function. In this study, laboratory experiments were designed to simulate perfect harmonic ocean wave motion by a dynamic simulator, in order to verify the present idea. It was identified average 4% bias on the vertical displacements between simulated and GPS derived, identifying the reasonable result from present GPS wave measurement approach. Field test was also carried out in this study. The GPS receiver was installed on a buoy and the derived significant wave height and mean wave period were compared with the buoy measurements by accelerometer. Field experiment showed approximate trend from buoy measured and GPS derived but an improvability results in quantification was found.

The process based numerical simulation of extreme storm surge water levels, currents and waves in coastal and shelf seas requires the correct specification of surface boundary conditions like atmospheric pressure and wind fields in space and time. These values are commonly derived from large scale (eg. global) climate models, satellite observations, or re-analysis products. Global meteorological information typically is provided on coarse grids at large time intervals, thus the application to small scale hydrodynamic models of higher spatial and temporal resolution must involve dynamic data downscaling. However, highly resolved regional climate simulations nested into global models are not always feasible. Whereas a direct linear interpolation in space may be possible even in the case of pronounced storms, a linear temporal interpolation can lead to unrealistic results. Thus we propose a simple algebraic algorithm to allow for the direct interpolation of gridded global meteorological data taking into account storm trajectories. The procedure is tested in the North Sea region where comprehensive data sets are available for the direct validation and the determination of the added value for hydrodynamic modelling.

The parameters in numerical wave models need to be calibrated be fore a model can be applied to a specific region. In this study, we selected the 8 most important parameters from the source term of the WAVEWATCH III model and subjected them to sensitivity analysis to evaluate the sensitivity of the WAVEWATCH III model to the selected parameters to determine how many of these parameters should be considered for further discussion, and to justify the significance priority of each parameter. After ranking each parameter by sensitivity and assessing their cumulative impact, we adopted the ARS method to search for the optimal values of those parameters to which the WAVEWATCH III model is most sensitive by comparing modeling results with ob served data at two data buoys off the coast of north eastern Taiwan; the goal being to find optimal parameter values for improved modeling of wave development. The procedure adopting optimal parameters in wave simulations did improve the accuracy of the WAVEWATCH III model in comparison to default runs based on field observations at two buoys.

Global datasets produced by the Geophysical Fluid Dynamics Laboratory for the 1979 summer season are used to study the observed three-dimensional structure of the tropical 30–50 day oscillation. Decomposition of them data onto horizontal and vertical functions obtained as solutions of a linearized primitive equation model reveals a dominant vertical structure with a 256 m equivalent depth, a zonal wavenumber 1, and meridional structures projecting mainly on the two Rossby modes with largest meridional length (R1 and R2) and on the Kelvin (K) model. The R1 and K modes exhibit a regular eastward propagation circling the globe 2.5 times during the 16-week period studied here. The amplitude of the K mode is smaller than that of the RI mode. Correlations with outgoing longwave radiation values are presented that show the 200 mb Kelvin westerly maximum located about 45° long east of the outgoing longwave radiation minimum. The Kelvin mode phase speed remains constant during this period. Some evidence i...