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maximum difference in sensible and latent heat fluxes can be about 30 W/m 2 , the mean values for latent heat fluxes are 22.27 W/m 2 for January and 5.40 W/m 2 for July. For sensible heat, they are 2.82 W/m 2 for January and 5.64 W/m 2 for July. We show that the maximum difference in net radiative fluxes can be as high as 55 W/m 2 , for January, the mean difference in net SW is 6.31 W/m 2 and in net LW it is 12.14 W/m 2 . For July, the respective differences are 29.99 W/m 2 for the SW and 14.31 W/m 2 for the LW. Relationships between the fluxes and satellite derived surface wind speed, total precipitable water, and cloud cover provide insight on the dominant processes that control the net heat flux. This study is intended to present an estimate of uncertainties that still exist in the net heat flux at the ocean-atmosphere interface.

The spatial pattern of latent heat flux (LHF) variability associated with El Nino-Southern Oscillation (ENSO) is extracted using 15 years (1993–2007) of monthly satellite-derived LHF over the global ocean. This ENSO LHF footprint agrees well with the El Nino evaporation pattern reported previously with a 3-year (1996–1998) weekly version of this data set. LHF anomalies over the eastern tropical Pacific are positively correlated with sea surface temperature (SST) anomalies suggesting a damping effect on ENSO. Positive correlations with ENSO are also observed over the eastern mid-latitude North Pacific, western and central mid-latitude South Pacific and the equatorial Indian Ocean. Negative correlations are observed elsewhere. It is also shown that the LHF footprints of both phases of ENSO (El Nino and La Nina) present very similar spatial structure. As expected, the surface wind pattern associated with El Nino (La Nina) shows convergence (divergence) over the central and eastern tropical Pacific and diverg...

The West African Monsoon region is of great concern due to the negative ecological, economical, and societal impacts of the persistent drought. Our results support the established postulation that the onset of summer rain in the southern region is associated with the migration of the inter-tropical convergence zone and in phase with the meridional moisture transport from the Gulf of Guinea. We present recent satellite measurements that illustrate the phase shift of the precipitation in the northern region, the Sahel, with respect to the region to the south. These satellite data and associated analysis techniques let us combine the effect of the onshore flow at the surface and offshore transport aloft to demonstrate with sufficient clarity that the depth-integrated moisture advection across the west coast, from the open Atlantic Ocean into the Sahel region, is in-phase with the annual and inter-annual variations of Sahel rainfall, but out-of-phase with rainfall in the southern region around the Gulf of Guinea. The peak Sahel rainfall is associated with the short-lived net moisture influx from the Atlantic, which may interact with local instability related to the African Easterly Waves. The data show two precipitation regimes in Western Africa Monsoon region associated with moisture input from two different regions of the ocean.

Over the last 100 years, boundary layer meteorology grew from the subject of mostly near-surface observations to a field encompassing diverse atmospheric boundary layers (ABLs) around the world. From the start, researchers drew from an ever-expanding set of disciplines—thermodynamics, soil and plant studies, fluid dynamics and turbulence, cloud microphysics, and aerosol studies. Research expanded upward to include the entire ABL in response to the need to know how particles and trace gases dispersed, and later how to represent the ABL in numerical models of weather and climate (starting in the 1970s–80s); taking advantage of the opportunities afforded by the development of large-eddy simulations (1970s), direct numerical simulations (1990s), and a host of instruments to sample the boundary layer in situ and remotely from the surface, the air, and space. Near-surface flux-profile relationships were developed rapidly between the 1940s and 1970s, when rapid progress shifted to the fair-weather convective boundary layer (CBL), though tropical CBL studies date back to the 1940s. In the 1980s, ABL research began to include the interaction of the ABL with the surface and clouds, the first ABL parameterization schemes emerged; and land surface and ocean surface model development blossomed. Research in subsequent decades has focused on more complex ABLs, often identified by shortcomings or uncertainties in weather and climate models, including the stable boundary layer, the Arctic boundary layer, cloudy boundary layers, and ABLs over heterogeneous surfaces (including cities). The paper closes with a brief summary, some lessons learned, and a look to the future.

Boundary-layer secondary circulations or ‘roll vortices’ can have a significant influence on the turbulent exchange of momentum, sensible heat and moisture throughout the hurricane boundary layer. In this study, analyses of data from a WP-3D aircraft of the National Oceanic and Atmospheric Administration (NOAA) are presented. As part of the Coupled Boundary Layer Air-Sea Transfer (CBLAST)-hurricane experiment sponsored through the Office of Naval Research and NOAA’s annual hurricane research program, flights were conducted to investigate energy exchange across the air–sea interface. We present the first in-situ aircraft-based observations of rolls in the hurricane boundary layer and investigate their influence on energy and momentum exchange. The rolls detected in Hurricane Isidore (year 2002) have a characteristic wavelength of about 900 m, in good agreement with analyses of data from a synthetic aperture radar image captured by the Canadian Space Agency’s RADARSAT satellite in the same storm. Our analyses of the airborne data suggest that roll vortices may be a significant factor modulating the air–sea momentum exchange.

Consideration of the dependence of various components of the sea-surface heat and momentum fluxes on sea surface temperature (SST) leads to an explanation for the observed reduction in the horizontal temperature gradients in the uppermost layer of the ocean (a few to 10 m in depth). Horizontal temperature gradients within the mixed layer can be masked by a near-surface layer of warm water. This camouflage of horizontal temperature gradients has importance for the remote sensing of SST used by the fishing industry, for the estimation of acoustic transmission, and for the forecasting of hurricane development, among many uses of SST data. Diurnal warming conditions in the Straits of Florida are examined by a simulation calculation and by analysis of observations obtained on moorings deployed on the south-east Florida shelf. When there is net heating (i.e., the solar input is stronger than the combined latent, sensible and longwave radiative heat losses) the originally warmer water experiences less heating than the colder water, leading to a weakening of the horizontal SST gradients as seen by surface buoys or satellites. The warmer water also experiences more mixing and therefore less increase in temperature. The strongest effect of the diurnal heating on wind stress occurs when the SST starts out cooler than the air temperature and the atmosphere is stably stratified. Diurnal warming can then rapidly increase the SST above the air temperature because of reduced wind stress and reduced upper-ocean mixing. After that the wind stress increases as convectively driven turbulence contributes to the atmospheric exchange.

Sea surface temperature (SST) is a result of multiple interactions in air-sea processes. During days with strong insolation and low wind speed, there may be uneven net heating of the water layer near the surface of the ocean, when there are horizontal temperature gradients at the sea surface. Cooling of the water caused by evaporation, sensible, or longwave radiative, heat loss would be greater from warm water compared to that from relatively cold water. As a result, under low wind speed conditions and clear skies, the horizontal SST discontinuities, occurring at fronts, eddies, or in storm wakes, may diminish or even vanish. This phenomenon is illustrated here with some field and modelling results. The dependence on latitude and mean environmental conditions of the difference in warming on the cold and warm side of SST discontinuities is explored. The time dependence is important for the impact on remote sensing of SST, and it is found to be short enough that substantial masking of SST gradients can occur during the first six hours of the diurnal heating cycle, but the effect would continue to grow if calm and solar heating persist for several subsequent days. An integrated effect of this uneven net heating is seen in the seasonal masking of subsurface temperature gradients in the Gulf of Mexico and Florida Straits.

Surface fluxes of momentum, freshwater, and energy across the air–sea interface determine oceanic circulation and its variability at all timescales. The goal of this paper is to estimate and examine some ocean surface flux variables using satellite measurements. The remotely sensed data come from the European Remote Sensing (ERS) satellite scatterometer on ERS-2, NASA scatterometer (NSCAT), and several Defense Meteorological Satellite Program (DMSP) radiometers [Special Sensor Microwave Imager (SSM/I)] on board the satellites F10–F14. The sea surface temperature comes from daily analysis calculated from Advanced Very High Resolution Radiometer (AVHRR) measurements. This study focuses on the 9-month period (October 1996–June 1997) of the NSCAT mission. To ensure high quality of the merged surface parameter fields, comparisons between different satellite estimates for the same variable have been performed, and bias corrections have been applied so that they are compatible with each other. The satel...

A new geographic record of the oomycete Olpidiopsis feldmanni infecting the tetrasporophytic stage of the red alga Asparagopsis sp. from the Adriatic Sea, confirmed through morphological identification, allowed us to expand previous observations of this organism. Ultrastructural investigations of environmental material showed a large central vacuole and a cell wall thicker than previously reported from other basal oomycete pathogens of algae. Phylogenetic analysis closely associates O. feldmanni to O. bostrychiae concurrent with structural observations. This constitutes the first genetic characterisation of an Olpidiopsis species that was initially described before 1960, adding to the genetic data of 3 other marine Olpidiopsis species established and genetically characterised in the last 2 decades. The paper discusses concurrences of the ultrastructural observations made here and in previous studies of the marine Olpidiopsis species with those made on the freshwater species. © The authors 2015.

This article reviews several microwave instruments employed in research and analysis of tropical cyclones (TCs), typhoons, and hurricanes. The instruments discussed include scatterometers, microwave radiometers, synthetic aperture radars (SARs), and rain radar from space. Examples of the particular contribution by one or more of these instruments in analysis of several storms illustrate the comprehensive new views provided by the SeaWinds scatterometers, the detailed high-resolution wind field provided by RADARSAT-1 SAR, particularly inside and in the vicinity of hurricane “eyes,” and the presence of secondary flows in the region between rainbands in TCs. The high spatial resolution of precipitation data from the Tropical Rainfall Measuring Mission's rain radar, combined with scatterometer or SAR data, give a significant improvement in the details that can be seen from space, at the surface, and in the precipitating areas of TCs. The microwave instruments provide a penetrating view below the upper level cirrus clouds.

Far from land and surface ship observations, most tropical depressions are identified by examining images from geostationary satellites for the presence of rotation of the convective cloud masses. During the 1999 hurricane season, surface wind vectors obtained by the SeaWinds scatterometer on the QuikSCAT satellite for the tropical Atlantic and Caribbean Sea were examined to test the hypothesis that developing tropical depressions (TDs) could be observed with this satellite sensor, before identification by the traditional means. QuikSCAT was able to detect the presence of closed circulation in the surface winds before the systems were designated as depressions. The satellite's unprecedented large swath width of 1800 km allows twice a day observation of most of the tropical oceans. SeaWinds data can, therefore, provide valuable guidance that are an important addition to the tools available to the tropical cyclone forecasting community.

New results from turbulent flux measurements made over Lake Washington include the following: 1) The only direct measure of the vertical transport of the horizontal momentum, heat, and matter in the surface boundary layer is the so-called eddy correlation method. However, even if the measurement errors are negligible, the results obtained from point observations may show large scatter due to lack of stationarity and horizontal homogeneity in the turbulent field and to the sampling variability. Scatter may be greatly reduced by spatial averaging. In this study, such an effect is achieved by determining the surface roughness length, hence the neutral drag coefficient, from the measured wave height spectrum, which reflects the atmospheric input integrated over the fetch. Applicability and usefulness of the approach for general field measurements and remote sensing is discussed. 2) The evolution of the wave field observed on Lake Washington agrees in peak frequency and the slope of the equilibrium ra...

Two major campaigns (Surface of the Oceans, Fluxes and Interactions with the Atmosphere (SOFIA) and Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE)) devoted to the study of ocean-atmosphere interaction were conducted in 1992 and 1993, respectively, in the Azores region. Among the various platforms deployed, instrumented aircraft and ship allowed the measurement of the turbulent flux of sensible heat, latent heat, and momentum. From coordinated missions we can evaluate the sea surface fluxes from (1) bulk relations and mean measurements performed aboard the ship in the atmospheric surface layer and (2) turbulence measurements aboard aircraft, which allowed the flux profiles to be estimated through the whole atmospheric boundary layer and therefore to be extrapolated toward the sea surface level. Continuous ship fluxes were calculated with bulk coefficients deduced from inertial-dissipation measurements in the same experiments, whereas aircraft fluxes were calculated with eddy-correlation technique. We present a comparison between these two estimations. Although momentum flux agrees quite well, aircraft estimations of sensible and latent heat flux are lower than those of the ship. This result is surprising, since aircraft momentum flux estimates are often considered as much less accurate than scalar flux estimates. The various sources of errors on the aircraft and ship flux estimates are discussed. For sensible and latent heat flux, random errors on aircraft estimates, as well as variability of ship flux estimates, are lower than the discrepancy between the two platforms, whereas the momentum flux estimates cannot be considered as significantly different. Furthermore, the consequence of the high-pass filtering of the aircraft signals on the flux values is analyzed; it is weak at the lowest altitudes flown and cannot therefore explain the discrepancies between the two platforms but becomes considerable at upper levels in the boundary layer. From arguments linked to the imbalance of the surface energy budget, established during previous campaigns performed over land surfaces with aircraft, we conclude that aircraft heat fluxes are probably also underestimated over the sea.

Unprecedented views of surface wind fields in tropical cyclones thereafter TCs) are provided by the European Remote Sensing Satellite (ERS) C band scatterometer. Scatterometer measurements at C band are able to penetrate convective storms clouds, observing the surface wind fields with good accuracy. However the resolution of the measurements (50x50 km(2)) limits the interpretation of the scatterometer signals in such mesoscale events. The strong gradients of the surface wind existing at scales of a few kms are smoothed in the measured features such as the intensity and location of the wind maxima, and the position of the center. Beyond the ERS systems, the scatterometers on-board the ADEOS and METOP satellites, designed by the Jet Propulsion Laboratory and by the European Space Agency, respectively, will be able to produce measurements of the backscattering coefficient at about 25x25 km(2) resolution. A few sets of ERS-1 orbits sampling TC events were produced with an experimental 25x25 km(2) resolution. Enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a TC with a much better accuracy than at 50 km resolution. In addition, a better resolution reduces the geophysical noise (variability of wind speed within the cell and effect of rain) that dominates the radiometric noise and hence improves the definition of the backscattering measurements. A comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within TCs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds (< 20 m/s) in neutral conditions. Observations of the TOPEX-POSEIDON dual-frequency altimeter are also used for that purpose. Patterns of the surface winds in TCs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed.

New results on the diurnal variation of global oceanic precipitation are obtained by using one year's TOPEX (ocean TOPography EXperiment) and TMR (TOPEX Microwave Radiometer) data, derived from the dual-frequency (Ku and C band) capacity of the altimeter and the non-Sun-synchronous orbit of the satellite. The diurnal variation is characterized by a three-maximum structure which peaks at 00:00, 08:00, and 16:00 local time. The midnight-morning-afternoon maxima and dawn-noon-evening minima pattern seems to correlate with the results of most previous studies and to offer a unified picture of the diurnal variation of oceanic rainfall. A slight daytime (06:00-18:00) preference of oceanic precipitation appears to be significant in all seasons with the day/night ratio varying from 1.032 to 1.141 and the annual mean being 1.082. Examination of the geographical distribution of the timing of diurnal variation shows that the majority of the world oceans favour an afternoon maximum and an evening minimum. Moreover, t...

A global picture of wave damping by rain (WDBR), a phenomenon familiar to seafarers for centuries, has been so far unavailable owing to the fact that neither rules nor tools exist for its systematic measurement. The situation has changed following the launch of the first dual-frequency (5.3 GHz and 13.6 GHz) radar altimeter TOPEX, along with the three-frequency (18 GHz, 21 GHz, and 37 GHz) radiometer TMR (TOPEX Microwave Radiometer). In this study, a scheme for detecting possible WDBR using TOPEX/TMR data is proposed. The geographical distribution of identified WDBR is consistent with the simultaneous presence of high sea state and intensive rainfall. Frequent occurrences of WDBR are observed in the midlatitude of the two hemispheres, particularly in the Pacific Ocean. In contrast, WDBR rarely occurs in the majority of the tropical and subtropical oceans. The global seasonality of WDBR is found to be weak as a result of the hemispheric phase opposition of sea state and rainfall in their annual variations. Knowledge of spatial distribution and temporal variation of WDBR is useful in dealing with potential systematic biases in satellite wind and wave measurements due to rain/sea interaction. It would have been interesting to compare the WDBR with coincident estimates of global rainfall from the SSM/I (Special Sensor Microwave/Imager).

Development of microwave technologies and our ability to penetrate into Tropical Cyclones (TCs) by instrumented aircraft and observe from satellites have contributed much of the knowledge and understanding that exist today. We can now follow the structure and development of a storm from inception through the many stages towards a dangerous typhoon, hurricane or cyclone, as they are variously called around the globe. The data from satellite microwave radiometers, scatterometers, altimeters, Synthetic Aperture Radars (SARs), microwave sounders, a rain radar and a cloud profiling radar as well as coastal radars, airborne radars and microwave radiometers have all contributed to changing the fields of both TC research and TC operational forecasting.

During the Surface Wave Dynamics Experiment, direct measurements of momentum, heat, and water vapor fluxes were obtained from a mast on the foredeck of a SWATH (small water-plane area, twin hull) ship in deep water off the state of Virginia. Directional wave spectra were obtained simultaneously from a 6- or 3-wire wave-staff array mounted at the bow of the ship. One hundred and twenty-six 17-minute runs of flux and wave data obtained with the ship steaming slowly into the wind are examined for the effects of the relative direction of the wind sea and background swell on the momentum transfer. The adequacy of the inertial dissipation method, which depends on the high-frequency turbulent fluctuations for evaluating the wind stress, is also examined for any effects of swell. The results show that the presence of counter- and cross-swells can result in drag coefficients that are much larger than the value for a pure wind sea. The eddy correlation and inertial dissipation methods for measuring wind st...

The transfer coefficients for momentum and heat have been determined for 10 m neutral wind speeds (U-10n) between 0 and 12 m/s using data from the Surface of the Ocean, Fluxes and Interactions with the Atmosphere (SOFIA) and Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiments. The inertial dissipation method was applied to wind and pseudo virtual temperature spectra from a sonic anemometer, mounted on a platform (ship) which was moving through the turbulence held. Under unstable conditions the assumptions concerning the turbulent kinetic energy (TKE) budget appeared incorrect. Using a bulk estimate for the stability parameter, Z/L (where Z is the height and L is the Obukhov length), this resulted in anomalously low drag coefficients compared to neutral conditions. Determining Z/L iteratively, a low rate of convergence was achieved. It was concluded that the divergence of the turbulent transport of TKE was not negligible under unstable conditions. By minimizing the dependence of the calculated neutral drag coefficient on stability, this term was estimated at about -0.65Z/L. The resulting turbulent fluxes were then in close agreement with other studies at moderate wind speed. The drag and exchange coefficients for low wind speeds were found to be C-en x 10(3) = 2.79U(10n)(-1) + 0.66 (U-10n < 5.2 m/s), C-en x 10(3) = C-hn x 10(3) = 1.2 (U-10n greater than or equal to 5.2 m/s), and C-dn x 10(3) = 11.7U(10n)(-2) + 0.668 (U-10n < 5.5 m/s), which imply a rapid increase of the coefficient values as the wind decreased within the smooth flow regime. The frozen turbulence hypothesis and the assumptions of isotropy and an inertial subrange were found to remain valid at these low wind speeds for these shipboard measurements. Incorporation of a free convection parameterization had little effect.

The TOPEX/POSEIDON mission offers the first opportunity to observe rain cells over the ocean by a dual-frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three-frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR TMR data are used to test the performance of the index. The resulting rain frequency statistics show quantitative agreement with those obtained from the Comprehensive Ocean-Atmosphere Data Set (COADS) in the Intertropical Convergence Zone (ITCZ), while qualitative agreement is found for other regions of the world ocean. A recent finding that the latitudinal frequency of precipitation over the Southern Ocean increases steadily toward the Antarctic continent is confirmed by our result. Annual and seasonal precipitation maps are derived from the index. Notable features revealed include an overall similarity in rainfall pattern from the Pacific, the Atlantic, and the Indian Oceans and a general phase reversal between the two hemispheres, as well as a number of regional anomalies in terms of rain intensity. Comparisons with simultaneous Global Precipitation Climatology Project (GPCP) multisatellite precipitation rate and COADS rain climatology suggest that systematic differences also exist. One example is that the maximum rainfall in the ITCZ of the Indian Ocean appears to be more intensive and concentrated in our result compared to that of the GPCP. Another example is that the annual precipitation produced by TOPEX/TMR is constantly higher than those from GPCP and COADS in the extratropical regions of the northern hemisphere, especially in the northwest Pacific Ocean. Analyses of the seasonal variations of prominent rainy and dry zones in the tropics and subtropics show various behaviors such as systematic migration, expansion and contraction, merging and breakup, and pure intensity variations, The seasonality of regional features is largely influenced by local atmospheric events such as monsoon, storm, or snow activities. The results of this study suggest that TOPEX and its follow-on may serve as a complementary sensor to the special sensor microwave/imager in observing global oceanic precipitation.

A new method is developed to estimate daily turbulent airsea fluxes over the global ocean on a 0.25 degrees grid. The required surface wind speed (w(10)) and specific air humidity (q(10)) at 10m height are both estimated from remotely sensed measurements. w(10) is obtained from the SeaWinds scatterometer on board the QuikSCAT satellite. A new empirical model relating brightness temperatures (T-b) from the Special Sensor Microwave Imager (SSM/I) and q(10) is developed. It is an extension of the author's previous q(10) model. In addition to T-b, the empirical model includes sea surface temperature (SST) and airsea temperature difference data. The calibration of the new empirical q(10) model utilizes q(10) from the latest version of the National Oceanography Centre airsea interaction gridded data set (NOCS2.0). Compared with mooring data, the new satellite q(10) exhibits better statistical results than previous estimates. For instance, the bias, the root mean square (RMS), and the correlation coefficient values estimated from comparisons between satellite and moorings in the northeast Atlantic and the Mediterranean Sea are 0.04gkg(1), 0.87gkg(1), and 0.95, respectively. The new satellite q(10) is used in combination with the newly reprocessed QuikSCAT V3, the latest version of SST analyses provided by the National Climatic Data Center (NCDC), and 10m air temperature estimated from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses (ERA-Interim), to determine three daily gridded turbulent quantities at 0.25 degrees spatial resolution: surface wind stress, latent heat flux (LHF), and sensible heat flux (SHF). Validation of the resulting fields is performed through a comprehensive comparison with daily, in situ values of LHF and SHF from buoys. In the northeast Atlantic basin, the satellite-derived daily LHF has bias, RMS, and correlation of 5Wm(2), 27Wm(2), and 0.89, respectively. For SHF, the statistical parameters are 2Wm(2), 10Wm(2), and 0.94, respectively. At global scale, the new satellite LHF and SHF are compared to NOCS2.0 daily estimates. Both daily fluxes exhibit similar spatial and seasonal variability. The main departures are found at latitudes south of 40 degrees S, where satellite latent and sensible heat fluxes are generally larger.

We examine integrated water vapor fields and rain intensity patterns derived from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) for several rapidly deepening and non-rapidly deepening midlatitude cyclones in the North Atlantic. Our goal is to identify features in the satellite data unique to the rapidly deepening cases, and to explore how these data can potentially be used in the analysis and forecasting of these events.

Surface layer fluxes of sensible heat and water vapor were measured from a fixed platform in the North Sea during the Humidity Exchange over the Sea (HEXOS) Main Experiment (HEXMAX). Eddy wind stress and other relevant atmospheric and oceanic parameters were measured simultaneously and are used to interpret the heat and water vapor flux results. One of the main goals of the HEXOS program was to find accurate empirical heat and water vapor flux parameterization formulas for high wind conditions over the sea. It had been postulated that breaking waves and sea spray, which dominate the air-sea interface at high wind speeds, would significantly affect the air-sea heat and water vapor exchange for wind speeds above 15 m/s. Water vapor flux has been measured at wind speeds up to 18 m/s, sufficient to test these predictions, and sensible heat flux was measured at wind speeds up to 23 m/s. Within experimental error, the HEXMAX data do not show significant variation of the flux exchange coefficients with wind speed, indicating that modification of the models is needed. Roughness lengths for heat and water vapor derived from these direct flux measurements are slightly lower in value but closely parallel the decreasing trend with increasing wind speed predicted by the surface renewal model of Liu et al. [1979], created for lower wind speed regimes, which does not include effects of wave breaking. This suggests that either wave breaking does not significantly affect the surface layer fluxes for the wind speed range in the HEXMAX data, or that a compensating negative feedback process is at work in the lower atmosphere. The implication of the feedback hypothesis is that the moisture gained in the lower atmosphere from evaporation of sea spray over rough seas may be largely offset by decreased vapor flux from the air-sea interface.

Recent experiments measuring turbulence dissipation rates in the upper ocean can be divided into two types: those supporting an analogy between the upper ocean and lower atmosphere, with dissipation rates following wall layer behavior, and those finding oceanic dissipation rates to be much higher than wall layer predictions. In an attempt to reconcile these two diverse acts of observations, Terray et al. proposed a wave-dependent scaling of the dissipation rate based on the significant wave height and the rate of energy input from the wind to the waves. Their parameterization was derived from observations of strongly forced, fetch-limited waves, although they conjectured that it would apply in typical oceanic conditions as well. This paper reports new measurements of turbulent kinetic energy dissipation made in the North Atlantic Ocean from a SWATH ship during the recent Surface Waves Dynamics Experiments (SWADE).These data support the scaling of Terray et al., verifying its validity when applied...

The evolution of two marine cyclones across the North Atlantic and the North Pacific Oceans is followed with a combination of sequential passive and active microwave data. The special sensor microwave/imager (SSM/I) provides estimates of atmospheric parameters : integrated water vapor, precipitation, and ocean surface wind speed. The Geosat and ERS 1 altimeter data are used to derive sea state parameters along the satellite tracks : the significant wave height and the ocean surface wind speed. The SSM/I integrated water vapor gradients are used to locate and follow the evolution of the atmospheric fronts. In regions of precipitation, often located behind the atmospheric fronts, the SSM/I surface wind speed cannot be derived, while the Geosat and ERS 1 altimeter wind speed yields estimates of wind speed gradients across the fronts. It is shown that the combination of SSM/I and satellite altimeters permits additional observations of surface fronts with higher resolution both in space and time than those given in the National Meteorological Center analyses.

In HEXOS, a programme of coordinated laboratory, field and model studies, an international group of participants has extended the range of measurements of evaporation from the sea and has investigated the role of droplets in the transfer of water to the atmosphere. Predictions of a rapid rise in the evaporation coefficient at wind speeds above 15 m s-1 have not been substantiated. Wind stress measurements showed a relationship with wave age. New methods were developed for coping with flow distortion.

Heat flux estimates obtained using the inertial dissipation method, and the profile method applied to radiosonde soundings, are assessed with emphasis on the parameterization of the roughness lengths for temperature and specific humidity. Results from the inertial dissipation method show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. This method seems very attractive for estimating heat fluxes over the ocean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport terms in the turbulent kinetic energy budget, has to be included in order to determine the friction velocity with better accuracy. Using the profile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness length could not be obtained. The humidity roughness length values were compatible with those found using the inertial dissipation method.

Accurate measurement of fluctuations in temperature and humidity are needed for determination of the surface evaporation rate and the air-sea sensible heat flux using either the eddy correlation or inertial dissipation method for flux calculations. These measurements are difficult to make over the ocean, and are subject to large errors when sensors are exposed to marine air containing spray droplets. All currently available commercial measurement devices for atmospheric humidity require frequent maintenance. Included in the objectives of the Humidity Exchange over the Sea program were testing and comparison of sensors used for measuring both the fluctuating and mean humidity in the marine atmosphere at high wind speeds and development of techniques for the protection of these sensors against contamination by oceanic aerosols. These sensors and droplet removal techniques are described and comparisons between measurements from several different systems are discussed in this paper. To accomplish these goals, participating groups devised and tested three methods of removing sea spray from the sample airstream. The best performance was given by a rotating semen device, the “spray Ringer.” Several high-frequency temperature and humidity instruments, based on different physical principles, were used in the collaborative field experiment. Temperature and humidity fluctuations were measured with sufficient accuracy inside the spray removal devices using Lyman-α hygrometers and a fast thermocouple psychrometer. Comparison of several types of psychrometers (using electric thermometers) and a Rotronic MP-100 humidity sensor for measuring the mean humidity illustrated the hysteresis of the Rotronic MP-100 device after periods of high relative humidity. Confidence in the readings of the electronic psychrometer was established by in situ calibration with repeated and careful readings of ordinary hand-held Assman psychrometers (based on mercury thermometers). Electronic psychrometer employing platinum resistance thermometers perform very well.

During the Surface Wave Dynamics Experiment (SWADE), the swath ship Frederick G. Creed was equipped with an array of wave staffs for the estimation of wave directional spectra. This paper reports on the first such estimates taken from a ship at sea. An algorithm for removing the effects of the ship motion, including those resulting from the Doppler shifting of observed frequencies, is presented along with some results from the SWADE experiment. A comparison with directional wave spectra taken from a nearby buoy shows the fidelity of the method.

Based on a geometric optics model and the assumption of an isotropic Gaussian surface slope distribution, the component of ocean surface microwave emissivity variation due to large-scale surface roughness is parameterized for the frequencies and approximate viewing angle of the Special Sensor Microwave/Imager. Independent geophysical variables in the parameterization are the effective (microwave frequency dependent) slope variance and the sea surface temperature. Using the same physical model, the change in the effective zenith angle of reflected sky radiation arising from large-scale roughness is also parameterized. Independent geophysical variables in this parameterization are the effective slope variance and the atmospheric optical depth at the frequency in question. Both of the above model-based parameterizations are intended for use in conjunction with empirical parameterizations relating effective slope variance and foam coverage to near-surface wind speed. These empirical parameterizations are the subject of a separate paper.

Several methods are examined for correction of turbulence and eddy fluxes in the atmospheric boundary layer, two of them based on a potential-flow approach initiated by Wyngaard. If the distorting object is cylindrical or if the distance to the sensor is much greater than the size of the body, the undisturbed wind stress can be calculated solely from measurements made by the sensor itself; no auxiliary measurements or lengthy model calculations are needed. A more general potential-flow correction has been developed in which distorting objects of complex shape are represented as a number of ellipsoidal elements. These models are applied to data from three turbulence anemometers with differing amounts of flow distortion, operated simultaneously in the Humidity Exchange over the Sea (HEXOS) Main Experiment. The results are compared with wind-stress estimates by the inertial-dissipation technique; these are much less sensitive to local flow distortion and are consistent with the corrected eddy correl...

The cloud cover and cloud water content obtained from integration of a limited area mesoscale prediction model are compared with the corresponding quantities derived from AVHRR and SSM/I satellite data. The model has an elaborate condensation-cloud parameterization scheme, in which cloud water is a prognostic variable. From AVHRR data, both cloud cover and liquid water content are retrieved by utilization of radiances from the visible, near infrared and infrared channels. From the 37GHz polarization difference in the microwave data obtained from SSM/I measurements, liquid water content is interpreted; this is only possible over the sea. An important feature of this comparison exercise is that the retrieved data are distributed on the same grid as the model. The difference between the simulation and the analysed cloud fields can thus easily be quantified and exhibited on the model domain. It is demonstrated that this type of retrieved meteorological parameters constitutes potentially useful data samples for quantitative verification of model simulations. There are some weaknesses in the retrieval methods that have to be removed before we can have sufficient confidence in the data to make quantitative verification meaningful. Furthermore, calibration against cloud parameters obtained through other measurements is necessary, although the three data sets show a remarkably good agreement in pattern and range of magnitude in the liquid water content. Even if improvements are needed, the present study has made it possible to make inferences about some deficiencies in the parameterization scheme of the model. DOI: 10.1034/j.1600-0870.1991.t01-3-00006.x

Uncertainties in turbulent ocean-atmosphere heat flux estimates, both among the estimates and between them and ground truth, suggest that further comparisons are needed. We analyze estimates from the French Research Institute for Exploitation of the Sea (IFREMER) and the Woods Hole Oceanographic Institution's Objectively Analyzed air-sea Fluxes (WHOI OAFlux). The IFREMER products are based on satellite observations and the WHOI OAFlux ones on data from satellites, buoys, and ships assimilated into numerical analyses. We focus on the Atlantic sector (70 degrees W-30 degrees E, 45 degrees S-45 degrees N) during 1996-2005, where the variables that enter the bulk formulae for computing fluxes (wind speed, sea surface and air temperature, and specific humidity) can be evaluated against buoys in the Prediction and Research Moored Array in the Atlantic (PIRATA). Since WHOI assimilates PIRATA observations, we have added two independent buoy data sets: FETCH and ROMEO. To examine how each variable contributes to the difference between estimated and buoy fluxes, the method of Bourras (2006) is applied. His so-called Q terms showed that specific air humidity and air temperature contributed the most to the biases of IFREMER latent and sensible heat fluxes, respectively, at both independent buoys. For WHOI OAFlux products, deviations from FETCH values were mainly due to wind speed and sea surface temperature differences, while in comparison with ROMEO fluxes, WHOI OAFlux biases were primarily due to specific humidity and sea surface temperature estimates. Modified estimates of turbulent fluxes with the IFREMER approach using the 10 m specific humidity and air temperature products of Jackson et al. (2009) show significant improvement in three test cases at PIRATA buoys.

In this chapter we review several climatologically important variables with a history of observation from spaceborne platforms. These include sea surface temperature and wind vectors, altimetric estimates of sea surface height, energy and water vapor fluxes at the sea surface, precipitation over the ocean, and ocean color. We then discuss possible improvements in sampling for climate and climate change definition. Issues of consistency of different data sources, archiving and distribution of these types of data are discussed. The practical prospect of immediate international coordination through the concept of virtual constellations is discussed and applauded.

This chapter addresses the estimation of global surface winds, surface wind stress, latent heat flux, and sensible heat flux over the oceans with high spatial and temporal resolution using satellite radar and radiometer measurements. An overview of the physics of remotely sensed data, of methods and algorithms used to retrieve surface fluxes is provided. The retrievals are used to estimate regular in space and time surface parameters, requested for oceanic forcing function, over global ocean. The characteristics of the former are investigated at global and regional scales.

The Surface Wave Dynamics Experiment (SWADE) took place east of the U.S. Coast in the winter of 1990–1991. A major objective of the research program is to refine our understanding of the relationship between fluxes to the sea surface and the sea state as determined from directional wave spectra. Simultaneous measurements of turbulent fluxes of mass, momentum and energy between sea and air, with the directional wave spectra, were required to meet this objective. In this short article we describe the process of obtaining turbulent flux measurements from a small water-plane-area twin hull (SWATH) ship. We measured turbulent fluxes of momentum, heat and water vapor from a tall mast at the bow of the SWATH ship Frederick G. Creed by the eddy correlation method, while the ship was moving into the wind. Directional wave spectra were obtained from a wave staff array ahead of the bow of the ship. The motion of the ship was recorded and a coordinate rotation was performed for each data sample. After all instrument response and motion corrections have been accounted for, we compare our calculated turbulent fluxes with values computed from another standard method, viz. the inertial dissipation method. This approach is not susceptible to platform motion but relies on assumptions that are not always valid. However, the two methods agree on average within 12%, 20% and 31% for momentum, water vapor and heat fluxes, respectively.

This is a review of contributions to knowledge about tropical cyclones (TCs) and their precursors provided by five types of micorwave instruments carried on spaceborne platforms. They include radiometers, scatterometers, altimeters, synthetic aperture radars, SARs and rain radars. A few discoveries have been selected that have lead to improved diagnostics of tropical depressions and cyclones through their precipitation patterns and their wind fields. Some practical applications are included related to forecasting of intensity changes and possible flooding by heavy rains after a TC makes landfall. Other intriguing observations about hurricane eyes and vortex developments are included.

A detailed parameterization is developed for the contribution of the nonprecipitating atmosphere to the microwave brightness temperatures observed by the Special Sensor Microwave/Imager (SSM/I). The atmospheric variables considered include the viewing angle, the integrated water vapor amount and scale height, the effective tropospheric lapse rate and near-surface temperature, the total cloud liquid water, the effective cloud height, and the surface pressure. The dependence of the radiative variables on meteorological variables is determined for each of the SSM/I frequencies 19.35, 22.235, 37.0, and 85.5 GHz, based on the values computed from 16,893 maritime temperature and humidity profiles representing all latitude belts and all seasons. A comparison of the predicted brightness temperatures with brightness temperatures obtained by direct numerical integration of the radiative transfer equation for the radiosonde-profile dataset yielded rms differences well below 1 K for all four SSM/I frequencies.

Atmospheric and surface parameters retrieved from observations by satellites in the TIROS-N/NOAA series provide valuable information for meteorological investigations in the data-sparse polar regions. A pattern-recognition method for processing these observations, the Improved Initialization Inversion (3I) system, has been developed at Laboratoire de Meteorologie Dynamique (LMD). This technique has been applied to several satellite passes, and the capability of the TIROS-N Operational Vertical Sounder (TOVS) to provide a description of mesoscale atmospheric phenomena has been demonstrated. In addition, the Special Sensor Microwave/Imager (SSM/I) launched in June 1987 on a satellite in the United States Defense Meteorological Satellite Program (DMSP) allows a new insight into the mesoscale structures of cyclones over the ocean by providing estimates of atmospheric water vapor, cloud water and surface winds. TOVS and SSM/I-inferred parameters are presented and discussed for several cases, including polar lows, and the mutual contribution of these two types of satellite data is shown.

The aim of this article is to estimate surface latent heat fluxes in the vicinity of a rapidly deepening cyclone before and during its period of most rapid intensification. This is done with a bulk parameterization scheme and remotely sensed input data. A method for estimating the difference in specific humidity between the surface and a 10-m height is investigated using the Special Sensor Microwave/Imager-observed integrated water vapor field and a sea surface temperature analysis. The surface latent heat flux fields generally have estimated errors below 40 percent south of 40 deg N and outside the region of high integrated water vapor values associated with frontal bands. The method of estimating surface latent heat fluxes for the case study was found to be usable in most regions of the northwest Atlantic Ocean except for those locations directly adjacent to coastlines in instances of offshore flow and in the vicinity of surface fronts.

Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October-November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age. ONR

This paper represents a continuation of work begun by Petty and Katsaros (1990) on refining an attenuation-based technique for estimating rainfall parameters from polarized 37-GHz brightness temperatures. In the present work, Nimbus-7 SMMR normalized 37-GHz polarization differences P are compared with surface digital radar observations of oceanic precipitation, made during the Taiwan Area Mesoscale Experiment (TAMEX) for cases when the SMMR and the radar coverages of significant precipitation features were nearly simultaneous. After the radar data were corrected for range-dependent errors, relationships were determined between the 37-GHz P and the radar reflectivity factor Z. The relationship was used to generate a large set of simulated SMMR observations from all available TAMEX radar scans, to produce histograms and mean values of pixel-averaged rain rate as a function of P.

Until recently, the scarcity of meteorological observations over polar areas has limited studies of high-latitude weather systems, but now data from polar orbiting satellites offer a new opportunity to observe and describe these systems. TOVS data have been used successfully for delineating synoptic and sub-synoptic systems, since they provide the vertical temperature structure of the atmosphere; SSM/I observations have proved valuable for analysing storms through water vapour and rain determinations. These positive results prompted us to analyze simultaneous TOVS and SSM/I observations obtained during a cold air outbreak over the Norwegian Sea. After a description of the instruments and the retrieval schemes, the mutually supporting information from these two independent instruments is discussed. Implications for the monitoring of polar lows are presented. DOI: 10.1034/j.1600-0870.1992.t01-1-00002.x

Studies of midlatitude and tropical cyclones and regional weather and climate analyses are examined. Consideration is also given to studies of long swell, sea ice, and continental ice sheets with Seasat data. Many of these results of the Seasat mission were serendipitous. In preparation for the major NASA initiative for the next decade, the Earth Observing Satellite program, it was thought timely to bring some of the Seasat experiences to the fore, since valuable lessons can be learned from the successes and the failures (or omissions) of the Seasat program. Data have been obtained about: (1) the synergistic value of integrated overlapping sampling by several instruments, (2) the invaluable contribution of carefully planned surface measurements, and (3) the importance of retaining flexibility in the system (enough data retention) to allow unexpected and innovative analysis techniques. 72 refs.

With the atmospheric water-vapor content information available from the SEASAT and Nimbus-7 Scanning Multichannel Microwave Radiometers (SMMR), differences in water-vapor distribution between cyclonic storms in different regions of the global ocean can be examined in more detail than previously possible from radiosondes. SMMR-derived integrated water vapor is a robust and dependable variable of the same accuracy as integrated radiosonde soundings. In this study, maximum and minimum water-vapor content in the vicinity of cold fronts of 80 storms that occurred in the North Atlantic, North Pacific and Southern oceans are compared. North Atlantic storms were found to have significantly higher maximum and minimum water-vapor content near cold fronts on average than North Pacific or Southern ocean storms for both the warm and cold seasons. These differences are attributed to warmer sea surface temperatures and air temperatures in the North Atlantic, and higher baroclinity and consequently stronger upwa...

Results are presented from calculations of radiation budgets for the sea-ice and the open-water regimes in the marginal ice zone (MIZ) of the Fram Strait, from measurements of surface irradiances and meteorological conditions made during the 1984 Marginal Ice Zone Experiment. Simultaneous measurements on either side of the ice edge allowed a comparison of the open-water and the sea-ice environments. The results show significant differences between the radiation budgets of the two regimes in the MIZ. The open water absorbed twice as much radiation as did the ice, and the mean cooling rate of the atmosphere over water was approximately 15 percent larger than that over ice. Calculated fluxes and atmospheric cooling rates were found to compare well with available literature data.

Based on an interpretation of a field experiment it is argued that, due to breaking of wind waves in deep water, the dissipation of energy is restricted to a range of frequencies ω > ωg, much higher than the frequency ωm of the dominant waves. In this dissipation range the spectrum has the form S(ω) = βg2ω−5 where g is the acceleration due to gravity and β = 0.025. For spectral wave components at ω ≤ ωg, only a local balance between energy input from the wind and the weak, third-order, nonlinear interaction is important. Asymptotically as ω ≫ ωm the wind input becomes unimportant, and the wave spectrum has the Kitaigorodskii form of a Kolgomorov analog S(ω) = 2aϵ0⅓ g4/3 ω−4 where ϵ0 is a constant flow of mean energy per unit surface area through the spectrum dissipated at high frequencies (when multiplied by g and water density ρw). From a method of M. S. Longuet-Higgins we estimate the magnitude of the dissipation (due to wave breaking) and find the Kolmogorov constant to be a ≈ 0.6. When a mode...