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An air-sea interaction model that includes turbulent transport due to capillary waves (surface ripples) is developed. The model differs from others in that the physical premises are applicable to low wind speeds (10-m wind speed, U 10 Ͻ 5 m s Ϫ1) as well as higher wind speeds. Another new feature of the model is an anisotropic roughness length, which allows a crosswind component of the stress to be modeled. The influence of the angle between the mean wind direction and the mean direction of wave propagation is included in the anisotropic roughness length. Most models are not accurate at low wind speeds and tend to underestimate fluxes in low wind speed regions such as the tropical oceans. Improvements over previous models are incorporated in the momentum roughness length parameterization. In addition, the dimensionless constant in the relationship between the capillary wave component of momentum roughness length and friction velocity is reevaluated using both wave tank data and field data. The new value is found to be 0.06, a factor of 3 smaller than the original estimate of 0.18. Modeling the influence of capillary waves is shown to improve the accuracy of modeled surface fluxes and drag coefficients. Several sets of tropical observations are used to examine mean increases in modeled fluxes due to capillary waves. The changes in latent heat fluxes are compared to proposed increases due to convective overturning (sometimes called gustiness) and are found to be larger by a factor of 4. For U 10 Ͻ 7 m s Ϫ1 , the mean estimates for tropical fluxes of momentum and latent heat are found to increase by 0.004 N m Ϫ2 and 6 W m Ϫ2. * Deceased.

The latter half of the twentieth century can be characterized as a period of rising water levels on the Great Lakes, with record high levels in 1974 and 1986. Concurrent with these periods of high water level are reported periods of high shoreline damage and property loss. Water levels of the Great Lakes are determined by precipitation, evaporation , river outflow, and groundwater inflow, while wave energy is primarily a function of wind speed, duration, and fetch. A comparison between a recently completed long-term (1956-87) wave climate hindcast and historical lake levels for the Great Lakes shows a strong correlation between periods of high wave energy and high lake levels. Statistical comparison of these two time series indicates an approximately constant correlation from +24 months to-6 months, around a zero lag/lead. The causational link between increasing lake levels and more intense wind-generated waves appears to be related to significant changes in the climatology of Great Lake's basin cyclones. Support for this conclusion is provided by an apparent interdecadal climate change reflected by a marked shift in track lines of extratropical cyclones passing over the Great Lakes and by a parallel decrease in lake levels and wave energies in the time period from 1976 to 1978. Finally and perhaps most importantly, it is shown that periods of reported high shoreline damage and property loss correlate more directly to periods of high wave energy than to periods of peak water level.

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A simple coupled flux and sea state model is developed. It is applicable to low, moderate, and high wind speeds, with a nonarbitrary wave age. It is fully consistent with an atmospheric flux parameterization. The flux model includes the influence of capillary waves on surface stress, which dominate surface stress on a waveperturbed surface for U 10 Ͻ 7 m s Ϫ1. The coupled model is verified for conditions of local equilibrium and it is used to examine the influences of surface tension and capillary waves on the equilibrium sea state at low and moderate wind speeds (U 10 Ͻ 7 m s Ϫ1). Capillary waves can directly influence characteristics of the airflow (roughness length and friction velocity), and surface tension can directly influence wave characteristics (period, phase speed, and wave age). The influences of capillary waves and surface tension on wave characteristics are found to be noticeable for U 10 Ͻ 6 m s Ϫ1 , and are likely to be significant in most applications when U 10 Ͻ 5 m s Ϫ1. The conditions under which relations valid for higher wind speeds break down are discussed. The new sea state parameterization is an improvement over previous relations (which apply well for U 10 Ͼ 7 m s Ϫ1) because it is also applicable for low and moderate winds. The mean wind speed over most of the world's oceans is less than 7 m s Ϫ1 , so there is considerable need for such a parameterization. The nonarbitrary wave age is particularly important because of the influence of wave age on the shape and size of waves, as well as fluxes of momentum, heat, and moisture. Additional results include a criterion for the capillary cutoff, significant wave height, and dominant wave period (as functions of wind speed and wave age). Consistency with a flux parameterization is crucial because of the influence of atmospheric stability on surface stress, which influences wave characteristics. The modeled significant wave height for local equilibrium is shown to be consistent with several parameterizations. The modeled dominant period is a good match to that of the Pierson-Moskowitz spectrum when U 10 Ͼ 13 m s Ϫ1 ; however, for lower wind speeds, the modeled period differs significantly from that of the Pierson-Moskowitz spectrum. The new model is validated with field observations. The differences are largely due to the capillary cutoff, which was not considered by Pierson and Moskowitz.