Search Results (11)

Wave-induced mixing can enhance vertical mixing in the upper ocean, facilitating the exchange of heat and momentum between the surface and deeper layers, thereby influencing ocean circulation and climate patterns. Building on previous research, this study proposes a wave-induced mixing parameterization scheme (referred to as EXP3) specifically designed for typhoon periods. This scheme was integrated into the fully coupled ocean–wave–atmosphere model COAWST and applied to analyze Typhoon In-Fa (2021) as a case study. The simulation results were validated against publicly available data, demonstrating a good overall match with observed phenomena. Subsequently, a comparative analysis was conducted between the EXP3 scheme, the previous scheme (EXP2) and the original model scheme (EXP1). Validation against Argo and Drifter buoy data revealed that both EXP2 and EXP3, which include wave-induced mixing effects, resulted in a decrease in the simulated mixed layer depth (MLD) and mixed layer temperature (MLT), with EXP3 showing closer alignment with the observed data. Compared to the other two experiments, EXP3 enhanced vertical motion in the ocean due to intensified wave-induced mixing, leading to increased upper-layer water divergence and upwelling, a decrease in sea surface temperature and accelerated rightward deflection of surface currents. This phenomenon not only altered the temperature structure of the ocean surface layer but also significantly impacted the regional ocean dynamics. Full article

The traditional power prediction methods cannot fully take into account the differences and similarities between units. In the face of the complex and changeable sea climate, the strong coupling effect of atmospheric circulation, ocean current movement, and wave fluctuation, the characteristics of wind processes under different incoming currents and different weather are very different, and the spatio-temporal correlation law of offshore wind processes is highly complex, which leads to traditional power prediction not being able to accurately predict the short-term power of offshore wind farms. Therefore, aiming at the characteristics and complexity of offshore wind power, this paper proposes an innovative short-term power prediction method for offshore wind farms based on a Gaussian mixture model (GMM). This method considers the correlation between units according to the characteristics of the measured data of units, and it divides units with high correlation into a category. The Bayesian information criterion (BIC) and contour coefficient method (SC) were used to obtain the optimal number of groups. The average intra-group correlation coefficient (AICC) was used to evaluate the reliability of measurements for the same quantized feature to select the representative units for each classification. Practical examples show that the short-term power prediction accuracy of the model after unit classification is 2.12% and 1.1% higher than that without group processing, and the mean square error and average absolute error of the short-term power prediction accuracy are reduced, respectively, which provides a basis for the optimization of prediction accuracy and economic operation of offshore wind farms. Full article

The kinetic energy transfer between the atmosphere and oceans, called wind work, affects ocean dynamics, including near-inertial oscillations and internal gravity waves, mesoscale eddies, and large-scale zonal jets. For the most part, the recent numerical estimates of global wind work amplitude are almost five times larger than those reported 10 years ago. This large increase is explained by the impact of the broad range of spatial and temporal scales covered by winds and currents, the smallest of which has only recently been uncovered by increasingly high-resolution modeling efforts. However, existing satellite observations do not fully sample this broad range of scales. The present study assesses the capabilities of ODYSEA, a conceptual satellite mission to estimate the amplitude of wind work in the global ocean. To this end, we use an ODYSEA measurement simulator fed by the outputs of a km scale coupled ocean–atmosphere model to estimate wind work globally. The results indicate that compared with numerical truth estimates, the ODYSEA instrument performs well globally, except for latitudes north of 40${}^{\circ }$N during summer due to unresolved storm evolution. This performance is explained by the wide-swath properties of ODYSEA (a 1700 km wide swath with 5 km posting for winds and surface currents), its twice-a-day (daily) coverage at mid-latitudes (low latitudes), and the insensitivity of the wind work to uncorrelated errors in the estimated wind and current. Full article

Novaya Zemlya bora is a strong downslope windstorm in the east of the Barents Sea. This paper considers the influence of the Novaya Zemlya bora on the turbulent heat exchange between the atmosphere and the ocean and on processes in the ocean. Another goal of this study is to demonstrate the sensitivity of simulated turbulent fluxes during bora to model coupling between atmosphere, ocean and sea waves. In this regard, a high-resolution numerical simulation of one winter bora episode was carried out using the COAWST (Coupled-Ocean-Atmosphere-Wave-Sediment Transport) modeling system, which includes the atmospheric (WRF-ARW model), oceanic (ROMS model), and sea waves (SWAN model) components. As shown by the simulation results, in the fully coupled experiment, turbulent heat exchange is enhanced in comparison with the uncoupled experiment (by 3% on average over the region). This is due to the atmosphere-sea-waves interaction, and the results are highly sensitive to the choice of roughness parameterization. The influence of the interaction of the atmospheric and oceanic components on turbulent fluxes in this episode is small on average. Bora has a significant impact on the processes in the ocean directly near the coast, forming a strong coastal current and making a decisive contribution to the formation of dense waters. In the open sea, the bora, or rather, the redistribution of the wind and temperature fields caused by the orography of Novaya Zemlya, leads to a decrease in ocean heat content losses due to a decrease in turbulent heat exchange in comparison with the experiment with flat topography. Full article

Typhoon Kalmaegi (2014) in the South China Sea (SCS) is simulated using a fully coupled atmosphere–ocean–wave model (COAWST). A set of sensitivity experiments are conducted to investigate the effects of different model coupling combinations on the typhoon simulation. Model results are validated by employing in-situ data at four locations in the SCS, and best-track and satellite data. Correlation and root-mean-square difference are used to assess the simulation quality. A skill score system is defined from these two statistical criteria to evaluate the performance of model experiments relative to a baseline. Atmosphere–ocean feedback is crucial for accurate simulations. Our baseline experiment successfully reconstructs the atmospheric and oceanic conditions during Typhoon Kalmaegi. Typhoon-induced sea surface cooling that weakens the system due to less heat and moisture availability is captured best in a Regional Ocean Modeling System (ROMS)-coupled run. The Simulated Wave Nearshore (SWAN)-coupled run has demonstrated the ability to estimate sea surface roughness better. Intense winds lead to a larger surface roughness where more heat and momentum are exchanged, while the rougher surface causes more friction, slowing down surface winds. From our experiments, we show that these intricate interactions require a fully coupled Weather Research and Forecasting (WRF)–ROMS–SWAN model to best reproduce the environment during a typhoon. Full article

The oceanic response of the Taiwan Strait (TWS) to Typhoon Nesat (2017) was investigated using a fully coupled atmosphere-ocean-wave model (COAWST) verified by observations. Ocean currents in the TWS changed drastically in response to significant wind variation during the typhoon. The response of ocean currents was characterised by a flow pattern generally consistent with the Ekman boundary layer theory, with north-eastward volume transport being significantly modified by the storm. Model results also reveal that the western TWS experienced the maximum generated storm surge, whereas the east side experienced only moderate storm surge. Heat budget analysis indicated that surface heat flux, vertical diffusion, and total advection all contributed to changes in water temperature in the upper 30 m with advection primarily affecting lower depths during the storm. Momentum balance analysis shows that along-shore volume acceleration was largely determined by a combined effect of surface wind stress and bottom stress. Cross-shore directional terms of pressure gradient and Coriolis acceleration were dominant throughout the model run, indicating that the effect of the storm on geostrophic balance was small. This work provides a detailed analysis of TWS water response to typhoon passage across the strait, which will aid in regional disaster management. Full article

Tropical cyclone induced phytoplankton productivity is examined using a tropical cyclone version of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®). A four-component Nutrient–Phytoplankton–Detritus biological model is integrated into COAMPS to create a fully integrated air-ocean-wave-biology model. This study investigates the upper ocean physical and biological states before and after Hurricane Ivan traversed the central Gulf of Mexico, in mid-September 2004. Elevated concentrations of surface chlorophyll-a appear in the simulation two days after the passage of the tropical cyclone, and these results are spatially and temporally coherent with Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data for this time period. Model results reveal enhancement of chlorophyll-a in submesoscale filaments on the periphery of a warm-core eddy that are dominated by large values of lateral strain and relative vorticity at the surface. The vertical circulation of the filament, with its associated upward vertical motion, permits surface ventilation of cold, nitrogen-rich water and subsequent stimulation of primary biological production. Here, we show for the first time that coupled biological-physical submesoscale processes may be simulated via a fully integrated air-sea-wave-biology tropical cyclone model that provides a mechanistic explanation of the conspicuous features revealed in satellite ocean color imagery following Ivan. Full article

The ocean is the largest source of water vapor on the planet, while precipitation is the greatest in tropical oceans and coastal areas. As a strong convective weather, typhoons bring not only strong winds but also strong precipitations. The accurate prediction of rainfall and precipitation induced by typhoons is still difficult because of the nonlinear relationship between typhoon precipitation and physical processes such as typhoon dynamics, heat, cloud microphysics, and radiation. In order to fully describe the interaction between sea and air, we simulated rainfall distribution under the influence of a typhoon using a state-of-the-art, atmosphere–ocean-wave model considering a real typhoon over the South China Sea as a case study. The typhoon wind field, pressure field, and spatial and temporal distribution of rainfall were simulated on the basis of this coupled atmosphere–ocean-wave model. The spatial asymmetry distribution characteristics of typhoon wind field, pressure field, and rainfall were revealed by the simulation. The reasons for this asymmetric distribution were elaborated through a diagnostic analysis. Full article

Typhoons are major marine dynamic disasters that affect the coastal ocean areas of China. During a typhoon, the coupling dynamic factors, such as wind, waves, storm surges, and river runoff, greatly enhance the mass and energy exchange at the various interfaces of the ocean. A fully coupled atmosphere-wave-ocean model in the South China Sea (SCS) was established based on the WRF, SWAN, and ROMS models. The variation of sea surface salinity (SSS) and ocean subsurface salinity caused by Typhoon Kai-tak (201213) was analyzed by the fully coupled model, and the basic characteristics of the response of the upper ocean to the typhoon are given in this paper. The simulation results demonstrate that the salinity of the sea surface showed a sharp change during Typhoon Kai-tak, and it changed gradually after entering the recovery period. During the passage of Typhoon Kai-tak, the disturbance caused by strong winds strengthened the mixing process of the water in the Pearl River Estuary (PRE) and its adjacent waters. As the typhoon developed, under the influence of Ekman pumping, the mixing effect between the subsurface and the bottom and the upper water was obvious. Before the impact of Typhoon Kai-tak, the salinity had obvious stratification characteristics along the water depth. Due to the influence of the storm surge, the surface water with increased salinity was transported to the estuary, which led to an increase in the salinity of the estuary’s surface water. In this condition, it is highly likely for there to be saltwater intrusion. The salinity distribution characteristics of three schemes (ROMS model only, coupled WRF-ROMS model, and fully coupled WRF-SWAN-ROMS model) were compared in this study. In the fully coupled WRF-SWAN-ROMS model, the disturbance of the bottom water was the most obvious, and the salinity value was greater than that of the coupled WRF-ROMS model, which indicates that under the influence of waves, the mixing and exchange abilities were strengthened. Full article

Studying the sea–air interaction between the upper ocean and typhoons is crucial to improve our understanding of heat and momentum exchange between the atmosphere and the ocean. There is a strong heat flux exchange between the atmosphere and the ocean during the impact of a typhoon, and the physical fields, such as the wind field, wave field, flow field, and SST field, also interact with each other. A fully coupled Atmosphere–Wave–Ocean model in the South China Sea was established by the mesoscale atmospheric model WRF, wave model SWAN, and the regional ocean model ROMS based on the COAWST model system. Typhoon Kai-tak was simulated using this fully coupled model and some other coupled schemes. In this paper, the variation of sea surface temperature (SST) and ocean subsurface temperature caused by Typhoon Kai-tak is analyzed by the fully coupled model, and the basic characteristics of the response of the upper ocean to the typhoon are given. The simulation results demonstrate that the fully coupled WRF-SWAN-ROMS model shows that the typhoon passes through the sea with obvious cooling. In the cold eddy region, the sea surface temperature cools 4 to 5 °C, and the cooling zone is concentrated on the right side of the track. The change of sea surface temperature lags more than 12 h behind the change of sea surface height. The decrease of SST on the left side of the track was relatively small: ranging from 1.5 to 2.5 °C. The disturbance of typhoon causes the subsurface water to surge to the surface, changes the temperature distribution of the surface, and causes the mixing layer to deepen about 40 m to 60 m. The simulation results reveal the temporal and spatial distribution of sea temperature and mixed layer depth. The sea surface temperature field has an asymmetrical distribution in space and has a lag in time. The heat exchange at the air–sea interface is very strong under the influence of the typhoon. The heat exchange between the air and sea is divided into latent heat and sensible heat, and the latent heat generated by water vapor evaporation plays a dominant role in the heat exchange at the air–sea interface, which shows that the heat carried by the vaporization of the sea surface is one of the important factors for the decrease of sea temperature under the influence of the typhoon. Full article

In November 2011, an Atlantic depression affected the Mediterranean basin, eventually evolving into a Tropical-Like Cyclone (TLC or Mediterranean Hurricane, usually designated as Medicane). In the region affected by the Medicane, mean sea level pressures down to 990 hPa, wind speeds of hurricane intensity close to the eye (around 115 km/h) and intense rainfall in the prefrontal zone were reported. The intensity of this event, together with its long permanence over the sea, suggested its suitability as a paradigmatic case for investigating the sensitivity of a numerical modeling system to different configurations, air-sea interface parameterizations and coupling approaches. Toward this aim, a set of numerical experiments with different parameterization schemes and levels of coupling complexity was carried out within the Coupled Ocean Atmosphere Wave Sediment Transport System (COAWST), which allows the description of air-sea dynamics by coupling an atmospheric model (WRF), an ocean circulation model (ROMS), and a wave model (SWAN). The sensitivity to different initialization times and Planetary Boundary Layer (PBL) parameterizations was firstly investigated by running a set of WRF standalone (atmospheric-only) simulations. In order to better understand the effect of coupling on the TLC formation, intensification and trajectory, different configurations of atmosphere-ocean coupling were subsequently tested, eventually including the full coupling among atmosphere, ocean and waves, also changing the PBL parameterization and the formulation of the surface roughness. Results show a strong sensitivity of both the trajectory and the intensity of this TLC to the initial conditions, while the tracks and intensities provided by the coupled modeling approaches explored in this study do not introduce drastic modifications with respect to those resulting from a fine-tuned standalone atmospheric run, though they provide by definition a better physical and energetic consistency. Nevertheless; the use of different schemes for the calculation of the surface roughness from wave motion, which reflects the description of air-sea interface processes, can significantly affect the results in the fully coupled runs. Full article