In this paper a detailed global climatology of wind-sea and swell parameters, based on the 45-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) wave reanalysis is presented. The spatial pattern of the swell dominance of the earth’s oceans, in terms of the wave field energy balance and wave field characteristics, is also investigated. Statistical analysis shows that the global ocean is strongly dominated by swell waves. The interannual variability of the wind-sea and swell significant wave heights, and how they are related to the resultant significant wave height, is analyzed over the Pacific, Atlantic, and Indian Oceans. The leading modes of variability of wind sea and swell demonstrate noticeable differences, particularly in the Pacific and Atlantic Oceans. During the Northern Hemisphere winter, a strong north–south swell propagation pattern is observed in the Atlantic Ocean. Statistically significant secular increases in the wind-sea and swell significant wave heights are found in the North Pacific and North Atlantic Oceans.

[1] The turbulent mixing in thin ocean surface boundary layers (OSBL), which occupy the upper 100 m or so of the ocean, control the exchange of heat and trace gases between the atmosphere and ocean. Here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the OSBL in global climate models, which then leads to biases in sea surface temperature. One reason, we argue, is that current parameterizations are missing key surface-wave processes that force Langmuir turbulence that deepens the OSBL more rapidly than steady wind forcing. Scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing, and against buoyancy forcing. A global perspective on the occurrence of waveforced turbulence is developed using re-analysis data to compute these parameters globally. The diagnostic study developed here suggests that turbulent energy available for mixing the OSBL is under-estimated without forcing by surface waves. Wave-forcing and hence Langmuir turbulence could be important over wide areas of the ocean and in all seasons in the Southern Ocean. We conclude that surfacewave-forced Langmuir turbulence is an important process in the OSBL that requires parameterization.

, appearing abruptly at wave age co/Uw equal to 1.2. Turbulence spectra of the horizontal components were shown not to scale with height above the water surface, in contrast to vertical velocity spectra for which such a variation was observed in the low-frequency range. In addition, spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 -3 Hz. From a comparison with results from a previous study it was concluded that this turbulence is of the "inactive" kind, being brought down from the upper parts of the boundary layer by pressure transport.

A B S T R A C T Possible future changes in Baltic Sea acidÁbase (pH) and oxygen balances were studied using a catchmentÁsea coupled model system and numerical experiments based on meteorological and hydrological forcing datasets and scenarios. By using objective statistical methods, climate runs for present climate conditions were examined and evaluated using Baltic Sea modelling. The results indicate that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, the seasonal pH cycle will be amplified by increased biological production and mineralization. All examined scenarios indicate future acidification of the whole Baltic Sea that is insensitive to the chosen global climate model. The main factor controlling the direction and magnitude of future pH changes is atmospheric CO 2 concentration (i.e. emissions). Climate change and land-derived changes (e.g. nutrient loads) affect acidification mainly by altering the seasonal cycle and deep-water conditions. Apart from decreasing pH, we also project a decreased saturation state of calcium carbonate, decreased respiration index and increasing hypoxic area Á all factors that will threaten the marine ecosystem. We demonstrate that substantial reductions in fossil-fuel burning are needed to minimise the coming pH decrease and that substantial reductions in nutrient loads are needed to reduce the coming increase in hypoxic and anoxic waters.

Air-lake methane flux (FCH 4 ) and partial pressure of methane in the atmosphere (pCH 4a ) were measured using the eddy covariance method over a Swedish lake for an extended period. The measurements show a diurnal cycle in both FCH 4 and pCH 4a with high values during nighttime (FCH 4 ≈ 300 nmol m À2 s À1 , pCH 4a ≈ 2.5 μatm) and low values during day (FCH 4 ≈ 0 nmol m À2 s À1 , pCH 4a ≈ 2.0 μatm) for a large part of the data set. This diurnal cycle persist in all open water season; however, the magnitude of the diurnal cycle is largest in the spring months. Estimations of buoyancy in the water show that high nighttime fluxes coincide with convective periods. Our interpretation of these results is that the convective mixing enhances the diffusive flux, in analogy to previous studies. We also suggest that the convection may bring methane-rich water from the bottom to the surface and trigger bubble release from the sediment. A diurnal cycle is not observed for all convective occasions, indicating that the presence of convection is not sufficient for enhanced nighttime flux; other factors are also necessary. The observed diurnal cycle of pCH 4a is explained with the variation of FCH 4 and a changing internal boundary layer above the lake. The presence of a diurnal cycle of FCH 4 stresses the importance of making long-term continuous flux measurements. A lack of FCH 4 measurements during night may significantly bias estimations of total CH 4 emissions from lakes to the atmosphere.

The efficiency of transfer of gases and particles across the air-sea interface is controlled by several physical, biological and chemical processes in the atmosphere and water which are described here (including waves, large-and small-scale turbulence, bubbles, sea spray, rain and surface films). For a deeper understanding of relevant transport mechanisms, several models have been developed, ranging from conceptual models to numerical models. Most frequently the transfer is described by various functional dependencies of the wind speed, but more detailed descriptions need additional information. The study of gas transfer mechanisms uses a variety of experimental methods ranging from laboratory studies to carbon budgets, mass balance methods, micrometeorological techniques and thermographic techniques. Different methods resolve the transfer at different scales of time and space; this is important to take into account when comparing different results. Air-sea transfer is relevant in a wide range of applications, for example, local and regional fluxes, global models, remote sensing and computations of global inventories. The sensitivity of global models to the description of transfer velocity is limited; it is however likely that the formulations are more important when the resolution increases and other processes in models are improved. For global flux estimates using inventories or remote sensing products the accuracy of the transfer formulation as well as the accuracy of the wind field is crucial. IntroductionThe transfer of gases and particles across the air-sea interface depends not only on the concentration difference between the water and the air, but also on the efficiency of the transfer process. The efficiency of the transfer is controlled by complex interaction of a variety of processes in the air and in the water near the interface. Here we treat both gases and particles since the transfer, to some extent, is governed by similar mechanisms. Studies of transfer across the air-sea interface include a variety of methods and techniques ranging from laboratory studies, modeling and large-scale field studies. Various methods reach somewhat different conclusions, due to representation of different

Atmospheric and surface wave data from several oceanic experiments carried out on the Floating Instrument Platform (FLIP) and the Air–Sea Interaction Spar (ASIS) have been analyzed with the purpose of identifying swell-related effects on the surface momentum exchange during near-neutral atmospheric conditions and wind-following or crosswind seas. All data have a pronounced negative maximum in uw cospectra centered at the frequency of the dominant swell np, meaning a positive contribution to the stress. A similar contribution at this frequency is also obtained for the corresponding crosswind cospectrum. The magnitude of the cospectral maximum is shown to be linearly related to the square of the orbital motion, being equal to , where Hsd is the swell-significant wave height, the effect tentatively being due to strong correlation between the surface component of the orbital motion and the pattern of capillary waves over long swell waves. A model for prediction of the friction velocity from measurements of Hsd, np, and the 10-m wind speed U10 is formulated and tested against an independent dataset of ~400 half-hour measurements during swell, giving good result. The model predicts that the drag coefficient CD, which is traditionally modeled as a function of U10 alone (e.g., the COARE algorithm), becomes strongly dependent on the magnitude of the swell factor and that CD can attain values several times larger than predicted by wind speed–only models. According to maps of the global wave climate, conditions leading to large effects are likely to be widespread over the World Ocean.

Preface This techrical report describes research by Dr. Cardone that began in 1 966 and has been sponsored by three different contracts as its scope increased and as the many applications that it will have become apparent. The first application of this work is to use available data more intelligently in the development of numerical wave hindcasting and forecasting procedures. In 1964, a wave climatology for the North Atlantic was produced that used ship reports to generate the wind fields for the wave hindcasts. It took one half an hour on a CDC 1604 to generate the wind fields for every six hours for a year. Although the hindcasts gave quite good results, it was clear that higher resolution wind fields and a better theory for the winds in the planetary boundary layer would improve the quality of wave predictions. This report more than adequately makes up for the nalvet of previous wind field models in the planetary boundary layer. A second goal for this study was to aid in the development of the software to be used should radar scatterometry and passive microwave data become available from a spacecraft. The definition of the winds over the ocean depends on many factors. Work is actively in progress to combine the results of this paper with simulated data such as might be obtained from remote .sensing techniques so that an optimum analysis of the planetary boundary layer can be made. This report makes it possible to develop ways to use the widely scattered ship reports over the ocean obtained on a synoptic basis in an intelligent way for the extrapolation and interpolation of spacecraft data into areas not observed by ships. A numerical model of the North Atlantic Ocean is presently under development for the Office of Naval Research. For this model, the wind stress at the sea surface and the sensible and latent heat fluxes at the air sea boundary are needed. The procedures described in this report define the wind stress at the sea surface, the atmospheric stability and the air sea temperature differences on an oceanic scale.