Bulk aerodynamic algorithms are needed to compute ocean surface turbulent fluxes in weather forecasting and climate models and in the development of global surface flux datasets. Twelve such algorithms are evaluated and ranked using direct turbulent flux measurements determined from covariance and inertial-dissipation methods from 12 ship cruises over the tropical and midlatitude oceans (from about 5ЊS to 60ЊN). The four least problematic of these 12 algorithms based upon the overall ranking for this data include the Coupled Ocean-Atmosphere Response Experiment (COARE) version 3.0 and The University of Arizona (UA) schemes as well as those used at the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Aeronautics and Space Administration (NASA) Data Assimilation Office for version 1 of the Goddard Earth Observing System reanalysis (GEOS-1). Furthermore, the four most problematic of these algorithms are also identified along with possible explanations. The overall ranking is not substantially affected by the use of the average of covariance and inertialdissipation flux measurements or by taking into consideration measurement uncertainties. The differences between computed and observed fluxes are further evaluated as a function of near-surface wind speed and sea surface temperature to understand the rankings. Finally, several unresolved issues in terms of measurement and algorithm uncertainties are raised.

Abstract. We have measured the permittivity of representative samples of natural seawater, synthetic seawater, and aqueous NaC1 solutions over the frequency range 3-20 GHz, in 0.1-GHz steps and over the temperature range -2ø-30øC in 1 ø steps. Additional measurements have been made at spot frequencies (23.8, 36.5, and 89 GHz) and at selected temperatures between -2 ø and 30øC. The data from these measurements have allowed us to deduce an interpolation function for e(v, t, S) in the ranges 2 <-v <-20 GHz, -2 ø <-t <-30øC, and 20%0 <-S <-40%0 with a precision of 1%. If the frequency range is extended up to 40 GHz, the precision of the interpolation function is about 3%. The data have also allowed us to compare the permittivities of natural seawater, synthetic seawater, and aqueous NaC1 solution with the same salinities. Natural and synthetic seawater have the same permittivities within a 1% experimental error estimate. An aqueous NaC1 solution has a significantly different permittivity (up to about 6% difference, depending upon the frequency and temperature). IntroductionFor microwave remote sensing applications over the ocean using radars and radiometers, a precise knowledge of the emissivity and reflectivity properties of the sea surface is required. The dielectric permittivity of seawater e(v, t, S) for a frequency v, temperature t, and salinity S is a vital parameter in all models describing the interaction of a wind-roughened sea surface with microwave radiation.The main objectives of the research program were to (1) deduce an interpolation function for e(v, t, S) with a precision good enough to satisfy the technical improvements in radiometric sensitivities for use in radiative transfer models in the frequency range 1-100 GHz and (2) The goal of such models is to provide the permittivity and conductivity of seawater at any frequency as a function of the "salinity" and temperature. Such a model has to be based upon experimental data. We have found only three authors who report permittivity

Satellite-based datasets of surface turbulent fluxes over the global oceans are being evaluated and improved.O cean surface fluxes of heat, moisture, and momentum observed during field experiments show strong variability on temporal scales that range from the diurnal cycle to the life cycle of storms, and on spatial scales as small as that of an individual convective cloud. High-frequency variability (e.g., diurnal, storm scale) in tropical air-sea fluxes has been hypothesized to influence intraseasonal and interannual variability of the monsoon (e.g., Webster et al. 1998) and the Pacific Ocean warm pool and El Nino (e.g., Sui and Lau 1997;Fasullo and Webster 2000). At high latitudes, large variations in surface fluxes and sea surface temperature are seen in response to storms, which impact the temperature, density, and mixing in the upper ocean, further influencing the atmospheric dynamics and thermodynamics. Storm-scale events have been hypothesized (e.g., Marshall et al. 1998;Nardelli and Salusti 2000) to be associated with ocean convection in the high-latitude water mass formation regions, contributing to deep water formation and the global ocean thermohaline circulation. Ocean mixing induced by tropical cyclones might play an important role in driving the global ocean thermohaline circulation and, thereby,

A field experiment in the southwesternIndian Ocean provides new insights into ocean-atmosphere interactions in a key climatic region. W hile easterly trade winds blow year-round over the southern Indian Ocean, surface winds experience a striking reversal north of 10°S. During boreal summer, the low-level easterly flow penetrates northward, is deflected when crossing the equator, and forms the strong Indian monsoon jet. During boreal winter, northeasterly winds also bend while crossing the equator southward and form a weak low-level westerly jet between the equator and 10°S (Fig. la)

Abstract. As part of a measuring program dedicated to the analysis of the dielectric properties of seawater in the frequency range 3-89 GHz, a new dielectric permittivity model based on the standard Debye theory has been developed for remote sensing applications over the ocean below 40 GHz, together with polynomial interpolations at the millimeter frequencies 85.5 and 89 GHz. The aim of this paper is to test the relevance of these new dielectric measurements through statistical comparisons of radiative transfer predictions with satellite and airborne radiometric data between 18 and 89 GHz. A radiometric sensitivity analysis to the permittivity measurement errors is proposed, which yields a sea surface brightness temperature accuracy of at least 0.5 K below 20 GHz, 1 K at 24 GHz, and 1.5 K at 37 and 89 GHz. At frequencies less than 40 GHz, superiority of the revised Debye model is pointed out over the most commonly used model of Klein and Swift [1977]. At millimeter frequencies the new permittivity expressions deviate significantly from the standard Debye predictions, especially at low temperature, suggesting the influence of a second "high-frequency" Debye relaxation. Our comparisons with radiometric data at 89 GHz and in the channel 85.5V of the special sensor microwave imager tend to support this hypothesis. The results emphasize the importance of an adequate modeling of the complex permittivity of seawater as input to the surface emissivity models, at any frequency of the microwave spectrum, and augur interesting outputs in both in-flight calibration and interpretation of satellite data.