Atmosphere Wave Model Research Articles

A parameterization scheme for the floating wind farm in a coupled atmosphere–wave model (COAWST v3.7)

A parameterization scheme for the floating wind farm in a coupled atmosphere–wave model (COAWST v3.7)

A Global Coupled Atmosphere-Wave Model System Based on C-Coupler2. Part II: Preliminary Results

A global coupled atmosphere-wave model system (MPAS-NWW3) that consists of MPAS-A (Model for Prediction Across Scales-Atmosphere) and NWW3 (the Third Generation Wave Model, WAVEWATHCH III) with C-Coupler2 (the Community Coupler2) is demonstrated with a focus on the atmospheric results in global and the specific marine area in the year 2020. Results from the two-way coupled MPAS-NWW3 model and standalone MPAS-A are compared with reanalysis products. The coupled model performs better in terms of high wind speeds and long valid hours. This indicates that the coupled model has an obvious inhibitory effect on surface wind in areas with strong winds.

A Global Coupled Atmosphere-Wave Model System Based on C-Coupler2. Part I: Model Description

This study presents a global coupled atmosphere-wave model system (MPAS-NWW3) and its verification. The Community Coupler2 (C-Coupler2), a developed coupler, is used to couple the global wave configuration of the NWW3 (WAVEWATHCH III) with the global atmosphere configuration of the MPAS-Atmosphere model. Surface wind at 10 meters above sea level, temperature and specific humidity at 2 meters above sea level are the coupled variables for atmospheric component model, and significant wave height, average wave length and peak frequency are for wave component model. Some codes are added to the surface layer scheme and the effect of momentum flux induced by sea waves is taken into consideration in this paper. All the coupled variables, input or output the coupler are demonstrated their consistency in the MPAS-NWW3 coupled model.

Effects of Surface Wave-Induced Mixing and Wave-Affected Exchange Coefficients on Tropical Cyclones

Surface waves perform a crucial role in modulating tropical cyclone (TC) systems and have proved to be key for numerical TC predictions. In this study, we investigate the effects of wave-induced mixing and wave-affected surface exchange coefficients using a coupled ocean–atmosphere–wave model for two real TC cases: Shanshan (2018) and Megi (2010). The results demonstrate that wave-affected surface exchange coefficients enhance air–sea heat fluxes and have a significantly positive effect on simulated TC intensity, size, and strengthening process. In contrast, the wave-induced mixing has a negative impact on TC intensity and size and is not conducive to TC intensification and maintenance. The net effect of these two factors is a balance between the wave-affected positive contribution and the negative contribution from wave-induced sea surface temperature cooling. We find that the effect of wave-induced mixing on a TC system depends on the local thermal structure of the ocean. When the thermocline is weak and there is warm water at the wave-induced mixing penetration depth, the negative effect of the wave-induced mixing is weak. However, when there is cold subsurface water and a strong thermocline, wave-induced mixing has a significant impact, which exceeds the wave-driven positive feedback.

A Kilometer-Scale Coupled Atmosphere-Wave Forecasting System for the European Arctic

AbstractAccurately simulating the interactions between the components of a coupled Earth modelling system (atmosphere, sea-ice, and wave) on a kilometer-scale resolution is a new challenge in operational numerical weather prediction. It is difficult due to the complexity of interactive mechanisms, the limited accuracy of model components and scarcity of observations available for assessing relevant coupled processes. This study presents a newly developed convective-scale atmosphere-wave coupled forecasting system for the European Arctic. The HARMONIE-AROME configuration of the ALADIN-HIRLAM numerical weather prediction system is coupled to the spectral wave model WAVEWATCH III using the OASIS3 model coupling toolkit. We analyze the impact of representing the kilometer-scale atmosphere-wave interactions through coupled and uncoupled forecasts on a model domain with 2.5 km spatial resolution. In order to assess the coupled model’s accuracy and uncertainties we compare 48-hour model forecasts against satellite observational products such as Advanced Scatterometer 10 m wind speed, and altimeter based significant wave height. The fully coupled atmosphere-wave model results closely match both satellite-based wind speed and significant wave height observations as well as surface pressure and wind speed measurements from selected coastal station observation sites. Furthermore, the coupled model contains smaller standard deviation of errors in both 10m wind speed and significant wave height parameters when compared to the uncoupled model forecasts. Atmosphere and wave coupling reduces the short term forecast error variability of 10 m wind speed and significant wave height with the greatest benefit occurring for high wind and wave conditions.

Impact of ocean waves on offshore wind farm power production

Offshore wind energy has seen a steady increase in the latest years as it serves as an ideal alternative energy source to meet our renewable energy goals. Due to this increase in interest and in installations of offshore wind farms a better understanding of the impact of waves on the power production of wind farms in necessary. This wave-wind farm power production interaction has scarcely been examined, however, some exceptions of small scale large-eddy-simulations exist. Unfortunately, these studies are not able to take multiple wind farms under real weather conditions into account. Here, we show the power production and wake lengths of 1250 offshore wind turbines located in the German Bight simulated by a stand-alone atmospheric (WRF) model and a coupled atmosphere-wave (WRF-SWAN) model. The coupled atmosphere-wave model estimates larger (smaller) power production in case of waves and wind traveling in the same (opposed) direction compared to the stand-alone atmospheric model. The relative difference between the two models can be as much as 20% for the two-week averaged grid power production, while the difference in total power over this two-week period is equal to 9%. Moreover, the wind farm wake lengths of waves and wind traveling in the same (opposed) direction are longer (shorter) for the coupled atmosphere-wave model compared to the stand-alone atmospheric model. Here, the relative difference of the mean wake length between the two models can be up to 25%. This shows the importance of waves as a part of the offshore wind environment and can be an important factor in future wind assessment or power production estimation studies.

Tropical Cyclones in the Arabian Sea: overview and simulation of winds and storm-induced waves

Three recent Tropical Cyclones (TCs) over the Arabian Sea, i.e., the super cyclone Gonu, the low intense cyclone Ashobaa, and cyclone Phet (with an unusual track), are studied using a high-resolution atmosphere-wave model and observations. The reliable performances of both atmospheric and wave models were established using the available field measurements, in which the modeling improvement in comparison with the previous studies is met. The effects of input parameterizations on the wave and wind estimations in the presence of TCs were examined. TCs track and intensity were more sensitive to the microphysics and cumulus schemes. Concerning the multi and single peaked wave spectra, three steps of wave generation, growth, and dissipation were addressed. Bimodal seas and swells exist in both generation and dissipation stages, whereas the seas are dominant in the growth stage. The performance of Westhuysen was better in modeling the combination of seas and swells.

Analysis of Ashobaa tropical cyclone-induced waves in the Northern Indian Ocean using coupled atmosphere–wave modeling

The Tropical Cyclones play a significant role in the world natural disasters. At the time of the cyclones, the atmosphere and the ocean are constantly exchanging energy. In this study, spectral and statistical analyses of the waves affected by the Cyclone Ashobaa in the northern Indian Ocean were investigated. For this purpose, a Coupled Atmosphere–Wave model as a subsystem of COAWST (Coupled Ocean–Atmosphere–Wave–Sediment Transport) was employed. In this modeling system, the Weather Research and Forecasting model (WRF) and the Simulating Waves Near-Shore model (SWAN), were used. Four monitoring points were considered to analyze the waves in the northern Indian Ocean in the offshores of Mumbai, Karachi, Chabahar and Muscat. The results of wave simulation showed that, the wave height on the northeastern offshore of the Arabian Sea is higher than the wave height on the offshore of the Gulf of Oman. As a result, the east and northeast coasts of the Arabian Sea are mostly affected than the coasts of the Gulf of Oman by the Cyclone Ashobaa-induced storm surges and swells.

On the interaction of mesoscale eddies and a tropical cyclone in the Bay of Bengal

Oceanic eddies span over a wide range of sizes and affect the thermodynamic properties of water column. By modifying the thermal structure of the upper ocean, these eddies influence the air-sea heat exchange and, therefore, the strength of a tropical cyclone (TC) that passes over the eddy zone. To understand the interaction of tropical cyclone with different types of eddies (cyclonic and anticyclonic) over the Bay of Bengal (BoB) region, three idealized numerical experiments are performed using an atmosphere–ocean–wave coupled model. In these experiments, the atmospheric and wave models are forced by the realistic surface forcing (i.e. wind, pressure, heat and momentum fluxes) of the Vardah cyclone period (10–15 December 2016) in the BoB. The ocean model is initialized with three idealized conditions, i.e. horizontally constant profile of temperature and salinity throughout the model domain, idealized three-dimensional (3-D) temperature and salinity profiles in the area of 2° radius for cyclonic eddy and anticyclonic eddy. The 3-D eddy profile is placed in the path of TC Vardah track. The strength and radius of both idealized cyclonic and anticyclonic eddies are kept same. The model-simulated results of these three experiments were intercompared and it is found that the tropical cyclone interaction with an anticyclonic eddy had provided an ancillary strength to the TC by raising the tropical cyclone heat potential (TCHP) in comparison with other experiments. The utilization of coupled ocean–atmosphere–wave model had also provided a better representation of ocean–atmosphere coupled feedback processes during TC interaction with different eddies. The analysis of feedback processes depicted that the TC interaction with an anticyclonic eddy has raised the magnitude of its existing moist-static-energy comparative to the cyclonic eddy interaction case which resulted into an increase in the strength of the TC.

Simulation of extreme waves using coupled atmosphere-wave modeling system over the South China Sea

A real-time two-way coupled atmosphere-wave model in the South China Sea (SCS) has been established based on the atmosphere model WRF and the wave model SWAN in this study. We implement a nested computational grid along the SCS in the SWAN model and utilize the WRF model to provide high-resolution mesoscale wind field and pressure field over the SCS under the influence of typhoons. The numerical simulation of the typhoon waves generated by typhoon Kai-tak (1213), Rammasun (1409) and Hato (1713) had been carried out. The results of the numerical simulation are compared with the results of the field observation and the satellite altimeter. The verification results show that the coupled WRF-SWAN model has a high accuracy in the simulation of typhoon waves under the influence of typhoons in the SCS. The results of the simulation reveal the asymmetrical distribution of wind speed and typhoon wave height generated by typhoons in the space. The intensity of the typhoon on the right is greater than that on the left of the typhoon track. The real-time two-way coupled atmosphere-wave model based on the WRF model and the SWAN model can accurately simulate the dynamic process of typhoon and the temporal and spatial distribution of the typhoon waves generated by typhoons. According to the results of the coupled WRF and SWAN model, a corresponding relationship between typhoon wind speed and wave height was obtained, which was combined with the statistical data of typhoon occurring in the SCS during 1949–2019, the distribution characteristics of typhoon wave in the SCS had been simulated. The statistical data grid with a spatial accuracy of 0.5 degree of typhoon waves in the SCS had been established, and then the statistical wave height of typhoon in the SCS based on the Pearson-III distribution had been simulated. Eight characteristic locations have been identified in the SCS, the highest frequency and the hugest height of typhoon wave is near the Luzon Strait, the average of typhoon wave height is reached 9.2 m. The second is southern Taiwan in the eight different selected positions, and the statistical average value of typhoon wave height is close to 8.0 m. Comparison of the Paracel Islands, Spratly Islands and Dongsha Islands, the smallest statistical value of the typhoon wave height is the waves in Spratly Islands, with a mean value of 3.0 m, and the statistical mean value of typhoon wave height near the Paracel Islands and Dongsha Islands are about 6.0 m. Based on the statistical results, combined with the frequency of typhoon in the region, the distribution of typhoon wave height can be calculated at any location in the SCS, and it can be provide to some references for the design of the coastal and ocean engineering.

Evaluation of a roughness length parametrization accounting for wind–wave alignment in a coupled atmosphere–wave model

AbstractThe importance of wind energy as an alternative energy source has increased over the latest years with more focus on offshore winds. A good estimation of the offshore winds is thus of major importance for this industry. Up to now the effect of the wind–wave (mis)alignment has not yet been taken into account in coupled atmosphere–wave models to study the vertical wind profile and power production estimations of offshore wind farms. In this study the roughness length parametrization of Drennan et al. in 2003, and its extension addressing the wind–wave (mis)alignment proposed by Porchetta et al. in 2019, are investigated in the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model. This study shows that the yearly mean wind estimation at hub height (100 m) is improved by the roughness length parametrization of Porchetta et al. compared to Drennan. This is mainly due to the increased roughness of the former parametrization compare to the latter, even in aligned wind–wave conditions. This difference in roughness is caused by the dataset used to obtain the constants, deep‐water conditions versus mixed offshore conditions. Moreover, the roughness length parametrization of Porchetta et al. performs better in two of three alignment categories. Furthermore, similar model performances are obtained if we exclude the wind directions from the wind shadow zone of the measurement mast or the wind directions from the recently built Alpha Ventus wind farm, which is in close vicinity of the measurement mast. Investigating different wind conditions shows that the new roughness length parametrization of Porchetta et al. performs best for both offshore and onshore winds. Additionally, we show that the coupled model estimations of the vertical wind are only slightly affected by significant wave height estimations. Similar model performances for different accuracies of significant wave height estimations are presented. One exception is the perpendicular alignment category where the new roughness length of Porchetta et al. outperforms the roughness length of Drennan when investigating the wind estimations related to significant wave heights with a higher accuracy. The roughness length parametrization of Porchetta et al. reduced the power production overestimation of the coupled model from 5.7 to 2.8%. We also show that the standalone atmospheric model including the roughness length of Charnock in 1955 has a degraded performance compared to the coupled model including the roughness length parametrization of Porchetta et al. for yearly average wind profiles.

Response of Air–Sea Fluxes and Oceanic Features to the Coupling of Ocean–Atmosphere–Wave During the Passage of a Tropical Cyclone

A coupled ocean–atmosphere–wave model was used to assess the impact of model coupling on the simulations of air–sea fluxes, surface currents, waves, and temperature profile during the passage of a tropical cyclone (TC) Phailin in the Bay of Bengal. Four numerical experiments with different coupling configurations among the atmosphere, ocean, and wave models were carried out to identify differences in simulated atmospheric and oceanic parameters. The simulated track and intensity of Phailin agree well with the observations. The inter-comparison of model experiments with different coupling options highlights the importance of better air–sea fluxes in the coupled model as compared to the uncoupled model towards an improvement in the simulation of TC Phailin. The coupled model configurations overcome the cold bias (up to − 2 °C) in sea surface temperature simulated by the uncoupled ocean model. A higher magnitude of the surface drag coefficient in the uncoupled atmosphere model enhanced the bottom stress (> 2 N m−2). As a result of excess momentum transfer to the sea surface, the uncoupled ocean model produced stronger surface currents as compared to the coupled model. The inclusion of the wave model increases the sea surface roughness and, thereby, improves the wind speed and momentum flux at the air–sea interface. The maximum significant wave height in the coupled model was about 2 m lower than the uncoupled wave model. The model experiments demonstrate that the periodic feedback among the atmosphere, ocean, and wave models leads to a better representation of momentum and heat fluxes that improves the prediction of a tropical cyclone.

Impact of different sea surface roughness on surface gravity waves using a coupled atmosphere–wave model: a case of Hurricane Isaac (2012)

The complicated pattern of the chaotic ocean surface depends strongly on the interaction between wind and waves. An accurate representation of momentum and energy exchange at air–sea interface is very important for ocean modeling and climate studies. The exchange of momentum, heat, and moisture at the air–sea interface considered a fundamental process in the development of mesoscale atmospheric phenomena such as hurricanes and precipitating systems. Since these exchanges take place in the wave boundary layer, one cannot neglect the importance of ocean surface waves in modifying air–sea interaction processes. In this paper, the sensitivity of a regional coupled atmosphere–wave model to sea surface roughness parameterizations is discussed. In order to see the impact of sea spray in modifying the surface gravity waves, we have introduced a sea-spray parameterization in surface layer scheme of the atmospheric model. We have taken the case of Hurricane Isaac, formed in the Gulf of Mexico in 2012 for this study. It is observed that the newly added sea-spray scheme shows a better performance compared with three existing, well-known formulations. Thus, during extreme events, sea spray can play an important role in modifying the wind and wave height.

Wind and Wave Extremes from Atmosphere and Wave Model Ensembles

The present work develops an innovative approach to wind speed and significant wave height extreme value analysis. The approach is based on global atmosphere–wave model ensembles, the members of which are propagated in time from the best estimate of the initial state, with slight perturbations to the initial conditions, to estimate the uncertainties connected to model representations of reality. The low correlation of individual ensemble member forecasts at advanced lead times guarantees their independence and allows us to perform inference statistics. The advantage of ensemble probabilistic forecasts is that it is possible to synthesize an equivalent dataset of duration far longer than the simulation period. This allows the use of direct inference statistics to obtain extreme value estimates. A short time series of six years (from 2010 to 2016) of ensemble forecasts is selected to avoid major changes to the model physics and resolution and thus ensure stationarity. This time series is used to undertake extreme value analysis. The study estimates global wind speed and wave height return periods by selecting peaks from ensemble forecasts from +216- to +240-h lead time from the operational ensemble forecast dataset of the European Centre for Medium-Range Weather Forecasts (ECMWF). The results are compared with extreme value analyses performed on a commonly used reanalysis dataset, ERA-Interim, and buoy data. The comparison with traditional methods demonstrates the potential of this novel approach for statistical analysis of significant wave height and wind speed ocean extremes at the global scale.

The effects of sea spray and atmosphere–wave coupling on air–sea exchange during a tropical cyclone

Abstract. The study investigates the role of the air–sea interface using numerical simulations of Hurricane Arthur (2014) in the Atlantic. More specifically, the present study aims to discern the role ocean surface waves and sea spray play in modulating the intensity and structure of a tropical cyclone (TC). To investigate the effects of ocean surface waves and sea spray, numerical simulations were carried out using a coupled atmosphere–wave model, whereby a sea spray microphysical model was incorporated within the coupled model. Furthermore, this study also explores how sea spray generation can be modelled using wave energy dissipation due to whitecaps; whitecaps are considered as the primary mode of spray droplets generation at hurricane intensity wind speeds. Three different numerical simulations including the sea- state-dependent momentum flux, the sea-spray-mediated heat flux, and a combination of the former two processes with the sea-spray-mediated momentum flux were conducted. The foregoing numerical simulations were evaluated against the National Data Buoy Center (NDBC) buoy and satellite altimeter measurements as well as a control simulation using an uncoupled atmosphere model. The results indicate that the model simulations were able to capture the storm track and intensity: the surface wave coupling results in a stronger TC. Moreover, it is also noted that when only spray-mediated heat fluxes are applied in conjunction with the sea-state-dependent momentum flux, they result in a slightly weaker TC, albeit stronger compared to the control simulation. However, when a spray-mediated momentum flux is applied together with spray heat fluxes, it results in a comparably stronger TC. The results presented here allude to the role surface friction plays in the intensification of a TC.

On the use of a coupled ocean–atmosphere–wave model during an extreme cold air outbreak over the Adriatic Sea

An intense cold air outbreak affected the northern Adriatic Sea during winter 2012, determining an exceptional persistence of northeasterly Bora wind over the basin, which lasted for about 3weeks. The cold air coming from the Balkans produced icing in the Venice lagoon and very intense snowfall in the Apennines Mountains and even near the coasts.In order to understand the importance and role of air–sea interactions for the evolution of the atmospheric fields, simulations with the Weather Research and Forecasting (WRF) model encompassing the whole period have been performed using sea surface temperature (SST) fields with an increasing level of complexity. Starting from a large-scale static sea temperature, the SST in the initial and boundary conditions has been progressively made more realistic. First, a more refined field, retrieved from a satellite radiometer was used; then, the same field was updated every 6h. Next, the effect of including a simplified 1D ocean model reproducing the Oceanic Mixed Layer (OML) evolution has been tested. Finally, the potential improvements coming from a coupled description of atmosphere–ocean and atmosphere–ocean–waves interactions have been explored within the Coupled Ocean–Atmosphere–Wave Sediment Transport (COAWST) modeling system.Results highlight that the energy exchange between air and sea does not significantly impact the atmospheric fields, in particular 10m wind and 2m temperature, also because of the geography of the basin and the predominance of synoptic-scale flow in intense events of Bora, in the northern Adriatic. However, when sensible and latent heat fluxes, which are dependent on atmospheric and oceanic variables, are analyzed, the more realistic representation of SST drastically improves the model performances.

Simulated Global Swell and Wind-Sea Climate and Their Responses to Anthropogenic Climate Change at the End of the Twenty-First Century

Abstract The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere–wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a time-slice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.

Ocean Warming Effect on Surface Gravity Wave Climate Change for the End of the Twenty-First Century

Abstract Surface wind (U10) and significant wave height (Hs) response to global warming are investigated using a coupled atmosphere–wave model by perturbing the sea surface temperatures (SSTs) with anomalies generated by the Working Group on Coupled Modeling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4)/Special Report on Emissions Scenarios A1B (SRES A1B) scenario late in the twenty-first century. Several consistent changes were observed across all four realizations for the seasonal means: robust increase of U10 and Hs in the Southern Ocean for both the austral summer and winter due to the poleward shift of the jet stream; a dipole pattern of the U10 and Hs with increases in the northeast sector and decreases at the midlatitude during boreal winter in the North Atlantic due to the more frequent occurrence of the positive phases of the North Atlantic Oscillation (NAO); and strong decrease of U10 and Hs in the tropical western Pacific Ocean during austral summer, which might be caused by the joint effect of the weakening of the Walker circulation and the large hurricane frequency decrease in the South Pacific. Changes of the 99th percentile U10 and Hs are twice as strong as changes in the seasonal means, and the maximum changes are mainly dominated by the changes in hurricanes. Robust strong decreases of U10 and Hs in the South Pacific are obtained because of the large hurricane frequency decrease, while the results in the Northern Hemisphere basins differ among the models. An additional sensitivity experiment suggests that the qualitative response of U10 and Hs is not affected by using SST anomalies only and maintaining the radiative forcing unchanged (using 1980 values), as in this study.

Global Ocean Surface Wave Simulation Using a Coupled Atmosphere–Wave Model

Abstract This study describes a 29-yr (1981–2009) global ocean surface gravity wave simulation generated by a coupled atmosphere–wave model using NOAA/GFDL’s High-Resolution Atmosphere Model (HiRAM) and the WAVEWATCH III surface wave model developed and used operationally at NOAA/NCEP. Extensive evaluation of monthly mean significant wave height (SWH) against in situ buoys, satellite altimeter measurements, and the 40-yr ECMWF Re-Analysis (ERA-40) show very good agreements in terms of magnitude, spatial distribution, and scatter. The comparisons with satellite altimeter measurements indicate that the SWH low bias in ERA-40 reanalysis has been improved in these model simulations. The model fields show a strong response to the North Atlantic Oscillation (NAO) in the North Atlantic and the Southern Oscillation index (SOI) in the Pacific Ocean that are well connected with the atmospheric responses. For the NAO in winter, the strongest subpolar wave responses are found near the northern Europe coast and the coast of Labrador rather than in the central-northern Atlantic where the wind response is strongest. Similarly, for the SOI in the Pacific Ocean, the wave responses are strongest in the northern Bering Sea and the Antarctic coast.

Impact of surface waves in a Regional Climate Model

A coupled regional atmosphere-wave model system is developed with the purpose of investigating the impact of climate changes on the wave field, as well as feed-back effects of the wave field on the atmospheric parameters. This study focuses on the effects of introducing a two-way atmosphere-wave coupling on the atmosphere as well as on wave parameters. The model components are the regional climate model RCA, and the third generation wave model WAM. Two different methods are used for the coupling, using the roughness length and only including the effect of growing sea, and using the wave age and introducing the reduction of roughness due to decaying sea (swell). Introducing a two-way coupling results in an altered frequency distribution of wind speed and wave heights. When only including growing sea the impact of waves on the long term mean atmospheric parameters is limited, inducing a reduction of wind speed and significant wave height. When also the impact of swell is introduced, there is a shift towards higher wind speeds as well as higher significant wave heights in the four investigated areas. There is a reduction of surface heat fluxes and a decrease in near surface temperature as well as a significant increase in near surface humidity. The major conclusion is that when introducing a more realistic surface description over sea, the air-sea interaction represented by waves has a significant impact also on long term averages of parameters in the atmosphere. Waves should thus be introduced in climate models for a realistic description of processes over sea.