Surface Wind Vector Research Articles

Potential Associations between Low-Level Jets and Intraseasonal and Semi-Diurnal Variations in Coastal Chlorophyll—A over the Beibuwan Gulf, South China Sea

Low-level jet (LLJ) significantly affects the synoptic-scale hydrometeorological conditions in the South China Sea, although the impact of LLJs on the marine ecological environment is still unclear. We used multi-satellite observation data and meteorological reanalysis datasets to study the potential impact of LLJs on the marine biophysical environment over the Beibuwan Gulf (BBG) in summer during 2015–2019. In terms of the summer average, the sea surface wind vectors on LLJ days became stronger in the southwesterly direction relative to those on non-LLJ days, resulting in enhanced Ekman pumping (the maximum upwelling exceeds 10 × 10−6 m s−1) in most areas of the BBG, accompanied by stronger photosynthetically active radiation (increased by about 20 μmol m−2 s−1) and less precipitation (decreased by about 3 mm day−1). These LLJ-induced hydrometeorological changes led to an increase of about 0.3 °C in the nearshore sea surface temperature and an increase of 0.1–0.5 mg m−3 (decrease of 0.1–0.3 mg m−3) in the chlorophyll-a (chl-a) concentrations in nearshore (offshore) regions. Intraseasonal and diurnal changes in the incidence and intensity of LLJs potentially resulted in changes in the biophysical ocean environment in nearshore regions on intraseasonal and semi-diurnal timescales. The semi-diurnal peak and amplitude of chl-a concentrations on LLJ days increased with respect to those on non-LLJ days. Relative to the southern BBG, LLJ events exhibit greater impacts on the northern BBG, causing increases of the semi-diurnal peak and amplitude with 1.5 mg m−3 and 0.7 mg m−3, respectively. This work provides scientific evidence for understanding the potential mechanism of synoptic-scale changes in the marine ecological environment in marginal seas with frequent LLJ days.

Twenty-Seven Years of Scatterometer Surface Wind Analysis over Eastern Boundary Upwelling Systems

More than twelve satellite scatterometers have operated since 1992 through the present, providing the main source of surface wind vector observations over global oceans. In this study, these scatterometer winds are used in combination with radiometers and synthetic aperture radars (SAR) for the better determination and characterization of high spatial and temporal resolution of regional surface wind parameters, including wind speed and direction, wind stress components, wind stress curl, and divergence. In this paper, a 27-year-long (1992–2018) 6-h satellite wind analysis with a spatial resolution of 0.125° in latitude and longitude is calculated using spatial structure functions derived from high-resolution SAR data. The main objective is to improve regional winds over three major upwelling regions (the Canary, Benguela, and California regions) through the use of accurate and homogenized wind observations and region-specific spatial and temporal wind variation structure functions derived from buoy and SAR data. The long time series of satellite wind analysis over the California upwelling, where a significant number of moorings is available, are used for assessing the accuracy of the analysis. The latter is close to scatterometer wind retrieval accuracy. This assessment shows that the root mean square difference between collocated 6-h satellite wind analysis and buoys is lower than 1.50 and 1.80 m s−1 for offshore and nearshore locations, respectively. The temporal correlation between buoy and satellite analysis winds exceeds 0.90. The analysis accuracy is lower for 1992–1999 when satellite winds were mostly retrieved from ERS-1 and/or ERS-2 scatterometers. To further assess the improvement brought by this new wind analysis, its data and data from three independent products (ERA5, CMEMS, and CCMP) are compared with purely scatterometer winds over the Canary and Benguela regions. Even though the four products are generally similar, the new satellite analysis shows significant improvements, particularly in the upwelling areas.

Ocean surface current multiscale observation mission (OSCOM): Simultaneous measurement of ocean surface current, vector wind, and temperature

Ocean current is one of the major drivers of water mass, energy, and biogeochemical cycles in the global ocean–atmosphere boundary layer and also a key variable in the formation of extreme climate events (e.g., El Niño). Direct measurement of the global ocean surface current is of great scientific interest and application value for understanding multiscale ocean dynamics, air-sea interaction, ocean mass and energy balance, and ocean carbon budget, as well as their variabilities under climate change. This paper reviews the state-of-the-art developments of ocean dynamics and technology on the observation of multiscale ocean circulation and related scientific frontiers. Presently, measurements of global ocean surface currents, which are mainly geostrophically derived from satellite altimeter data, are only available to resolve quasi-geostrophic current at large- to meso-scale in the off-equatorial open ocean. This becomes a bottleneck impeding the application and the development of ocean circulation dynamics. With the ambition of breaking the bottleneck, Ocean Surface Current multiscale Observation Mission (OSCOM) will launch a satellite equipped with a Doppler Scatterometer to directly measure ocean surface currents for the first time with a very high horizontal resolution of 5–10 km and a 3-day global coverage. Through carrying a Surface Temperature Infrared Radiometer and a Surface Temperature Microwave Radiometer, the OSCOM satellite is supposed to have the capability of observing ocean surface current, ocean surface vector wind, and sea surface temperature simultaneously. With a cutting-edge design, OSCOM will provide an in-depth picture of non-equilibrium ocean state and air-sea interaction from mesoscale to submesoscale, and helps to construct the fine structure of deep ocean current through a combination with Array for Real-time Geostrophic Oceanography profiling. Those direct measurements and derived dynamic parameters will further facilitate analyses of ocean carbon budget and ocean biogeochemical cycle, and provide a novel and improved pathway to data assimilation, coupling of General Circulation Models, and the Earth System Modelling for ocean prediction and climate change.

Weather-Driven Coastal Dynamics in a Tide-Dominated Area: Cases from Spring 2016 along the West Coast of Korea

Kim, B.-J.; Lee, D.E.; Ro, Y.-J., and Jeong, K.-Y., 2021. Weather-driven coastal dynamics in a tide-dominated area: Cases from Spring 2016 along the west coast of Korea. Journal of Coastal Research, 37(3), 494–505. Coconut Creek (Florida), ISSN 0749-0208.Analyses of current dynamics recorded using multilayer current meters in Spring 2016 (15 April–17 May, 32 d) at two stations near Kkotji Beach in Anmyeon-do, Yellow Sea, Korea, are presented. Harmonic analysis is applied to identify tidal characteristics in the study area. A slightly rotational current pattern is detected at ST01, while oscillations predominantly in north–south orientation are detected at ST02. Nontidal residual currents and the concurrent surface atmosphere data are analyzed together. Residual currents converge (diverge) between ST01 and ST02 following the increase (decrease) in thickness between two stations. Using advanced statistical methods, the spatial patterns of such dynamic events are shown with their association with surface atmosphere. Complex correlation analysis reveals that residual currents are significantly correlated with abrupt surface wind fluctuations associated with extratropical cyclones. The characteristics of residual currents and surface wind vectors are further analyzed, using complex empirical orthogonal functions (CEOF). The first residual current mode (R1) accounts for 46.8% of the total variation, while the second mode (R2) accounts for 24.9%. R1 represents a wind-induced component in the longshore direction, while R2 represents a bottom-driven component in the opposite direction. Both the modes correlate significantly with the first wind mode (W1, longshore wind), which leads the associated residual current modes by a few hours. Spectral analysis indicates that the two significant periods of surface wind and residual current modes are well matched to each other, exhibiting cycles of 1.6 and 4 days.

On the Generation of Daily Gridded Ocean Surface Vector Wind Products From Scatsat-1

An optimal interpolation (OI)-based technique is utilized to generate global daily gridded wind products from Scatsat-1 data. The first guess (i.e., background) for the OI is used from the analyses of National Centre for Medium Range Weather Forecasting (NCMRWF) global operational model. The generated gridded products are subsequently validated using observations from global moored buoys and surface winds analyses from European Centre for Medium-Range Weather Forecasts (ECMWF), and that shows a root mean square error of ~1.3 m/s in wind speed and ~19° in wind direction. Along with the gridded winds, several wind-dependent products (e.g., wind stress, wind divergence, wind stress curl, sensible and latent heat flux, etc.) are also generated. The gridded products from Scatsat-1 are available freely from Meteorological and Oceanographic Satellite Data Archival Center ( <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">http://www.mosdac.gov.in</uri> ) since October 03, 2016.

Extreme weather events related to climate change: widespread flooding in Iran, March–April 2019

This study investigates the extreme weather pattern accompanying the widespread flash flooding in unpredicted areas during mid-March to April of 2019 in Iran. During this time, the active weather frontal system with heavy and insistent rainfalls drenched Iran (mostly north, west and southern), Iraq and Turkey (eastern part). The climatological mean and anomalies of the meteorological datasets from the National Centers for Environmental Prediction (NCEP) reanalysis model are examined, and synoptic and dynamical patterns are compared. The anomaly weather maps are created for different parameters to show the abnormal features during the study period (months of March and April 2019) presenting significant differences from the thirty-year climate normals of the period 1981–2010. This research shows an intensified pressure gradient, strong vertical motion and strengthened 500 hPa mid-tropospheric westerly currents during the study period. The relative humidity at 850 hPa shows on average ~ 4–11% higher values than the climate normal. The surface wind vector analysis reveals the intensified south flows originated from Oman sea and the Indian Ocean providing rather warmer and wet air mass encounters with an abnormal regional colder surface air mass. Upper level wind vectors at 250 hPa and vertical profile of the meridional wind anomalies exhibit a wavy jet pattern compared to the climate normal structure along with the significant vertical meridional wind shear as the sign of climate change. These abnormal atmospheric changes can contribute to forming extreme weather development over the study area during the study period. Also, understanding the recent extreme atmospheric changes in the study area may contribute to a better future forecast when such floods may happen again.

Implications of the OEN mixture model of the mean wind vector for the generation of synthetic timeseries and for the assessment of extremes

This paper extends the results of the “fuzzy” OEN mixture model to estimate the probability densities, autocorrelations and spectra of the individual wind mechanisms within the mixed climates of Rome: Fiumicino and Ciampino, and discusses the implications for synthesising long-term simulation of the surface wind vector and for the assessment of extreme mean wind speeds. The paper confirms, from observations, that the strong diurnal effects observed at these locations are confined to a low range of wind speeds and do not significantly affect the extreme wind speeds for annual, or longer, epochs. A procedure is proposed to simulate exceptionally long timeseries of the mean wind vector from the OEN mixture model to examine convergence of the upper tail of the extreme wind speed distribution to the presumed asymptote.

How well is outer tropical cyclone size represented in the ERA5 reanalysis dataset?

The outer tropical cyclone (TC) size was extracted from the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation global atmospheric reanalysis (ERA5), the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), and the ECMWF Interim reanalysis (ERA-I), as well as a hybrid reanalysis-observation dataset, the Cross Calibrated Multi-Platform (CCMP) ocean surface wind vector product. Results are compared with the QuikSCAT Tropical Cyclone Radial Structure Dataset (QSCAT-R). Several size metrics were applied including the radii of 6–15 m s−1 winds. The capability of ERA5 in describing TC outer wind fields was evaluated, and improvements in the representation of outer size assessed.The ERA5 reanalysis can resolve stronger TC winds, which leads to more valid outer size samples, especially for the radii of 12 and 15 m s−1 winds, and for the cases with outer sizes of <300 km. This makes the distribution characteristics of the outer size in the ERA5 reanalysis closer to the observation. These improvements of ERA5 are more obvious in the eastern North Pacific basin where TCs are generally of smaller size. However, ERA5 still underestimates the outer size, similarly to its predecessor ERA-I. The size error in ERA5 becomes more negative with increasing observed outer size, with this tendency also occurring in previous reanalysis datasets. Nevertheless, among the size metrics examined, the radius of 9 m s−1 winds is regarded as the optimal size metric for examining the extent of outer winds, thus providing an effective reference for constructing an objective, multi-decadal dataset of outer size using the ERA5 reanalysis.

Global Forecast Impact of Low Data Latency Infrared and Microwave Sounders Observations from Polar Orbiting Satellites

The Direct Broadcast Network (DBNet) provides near-real-time delivery of low-earth-orbiting (LEO) meteorological satellites to operational numerical weather prediction (NWP) systems that need short data cut-off times to allow for the assimilation of the most recent satellite measurements. The NWP model requires timely delivery of observations including atmospheric temperature, humidity, and surface wind vectors. The World Meteorological Organization (WMO) Space Program (WSP) recommends the data latency of no more than 20 min for the satellite measurements. Currently, not all DBNet stations are delivering satellite data within the 20-min time frame. In this study, the forecast impact of the observations of LEO satellite sounders with data latency of 20 min or less was evaluated using the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). Reducing the data latency up to 5 min increases the number of LEO infrared (IR) and microwave (MW) sounder observations delivered to the NCEP GFS data assimilation system by more than 20%. Overall, this study demonstrates a positive impact on the global weather forecasts when the IR and MW sounder data are delivered by 20 min anywhere in the world. Additional forecast benefits are not obvious for shorter data latency. Results from this study support the WSP recommendation of 20–minute data latency.

First Results From the Rotating Fan Beam Scatterometer Onboard CFOSAT

The first rotating fan beam scatterometer onboard China-France Oceanography Satellite (CFOSAT) was successfully launched on October 29, 2018. CFOSAT SCATterometer (CSCAT) is dedicated to the monitoring of sea surface wind vectors but also provides valuable data for the applications over land and Polar Regions. This article provides an overview of the relevant procedures of CSCAT data processing, including onboard signal processing and operational ground processing. Then a post-launch analysis is carried out to evaluate the first results of CSCAT L1 and L2 products. It shows that the CSCAT instrument is generally stable in terms of noise measurements and internal calibration, unless there is any important change in the system configuration. Specifically, the CSCAT backscatter (σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sup> ) precision and wind quality are studied using a set of collocated ancillary data. The σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sup> precision degrades as wind speed decreases, and it is relatively low at high incidence angles (e.g., θ >46°). In particular, backscatter estimation of the horizontally polarized beam should be further improved by correcting the noise subtraction factor. The retrieved CSCAT winds are in good agreement with the European Centre for Medium Range Weather Forecasts (ECMWF) winds, the Advanced Scatterometer (ASCAT) winds, as well as the buoy winds. However, due to unresolved calibration and interbeam consistency problems, the wind quality degrades remarkably for the out-swath and the nadir-region wind vector cells, implying that the σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sup> calibration should be improved in the future updates.

Measuring Winds and Currents with Ka-Band Doppler Scatterometry: An Airborne Implementation and Progress towards a Spaceborne Mission

Ocean surface winds and currents are tightly coupled, essential climate variables, synoptic measurements of which require a remote sensing approach. Global measurements of ocean vector winds have been provided by scatterometers for decades, but a synoptic approach to measuring total vector surface currents has remained elusive. Doppler scatterometry is a coherent burst-scatterometry technique that builds on the long heritage of spinning pencil beam scatterometers to enable the wide-swath, simultaneous measurement of ocean surface vector winds and currents. To prove the measurement concept, NASA funded the DopplerScatt airborne Doppler scatterometer through the Instrument Incubator Program (IIP) and Airborne Instrument Technology Transition (AITT) program. DopplerScatt has successfully shown that pencil beam Doppler scatterometry can be used to form wide swath measurements of ocean winds and currents, and has increased the technology readiness level of key instrument components, including: Ka-band pulsed radar hardware, optimized scatterometer burst-mode operation, calibration techniques, geophysical model functions, and processing algorithms. With the promise and progress shown by DopplerScatt, and the importance of air-sea interactions in mind, the National Academy’s Decadal Survey has targeted simultaneous measurements of winds and currents from a Doppler scatterometer for an Earth Explorer class spaceborne mission. Besides DopplerScatt’s place as a technology stepping stone towards a satellite mission, DopplerScatt provides scientifically important measurements of ocean currents and winds (400 m resolution) and their derivatives (1 km resolution) over a 25 km swath. These measurements are enabling studies of the submesoscales and air-sea interactions that were previously impossible, and are central to the upcoming NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE). This paper summarizes the development of DopplerScatt hardware, systems, calibration, and operations, and how advances in each relate to progress towards a spaceborne Doppler scatterometer mission.

Ocean Vector Wind Retrievals From TRMM Using a Novel Combined Active/Passive Algorithm

This article presents a novel ocean vector wind (OVW) retrieval algorithm for remote sensing of ocean winds, using the precipitation radar (PR) and tropical rainfall measurement mission (TRMM) microwave imager (TMI) that operated for >17 years on the TRMM observatory. In this study, the wind speed and anisotropic wind direction (WD) characteristics of the ocean backscatter and brightness temperature (Tb) were empirically characterized to produce geophysical model functions for 49 PR beam positions and three TMI frequency channels (10, 19, and 37 GHz). For passive TMI measurements, the modified second stokes parameter (weighted difference of V and H-pol Tb's) was used to cancel the atmosphere contribution, which enhances the WD signal. Thus, combining linearly polarized Tb measurements with the anisotropic backscatter signature of the Ku-band PR, the feasibility of retrieving ocean surface wind vector is demonstrated. The OVW retrieval algorithm is validated by comparing retrievals with collocated numerical weather models wind vectors, and the statistics of OVW retrieval accuracy is presented.

Evaluation of Spaceborne GNSS-R Retrieved Ocean Surface Wind Speed with Multiple Datasets

Spaceborne Global Navigation Satellite Systems-Reflectometry (GNSS-R) can estimate the geophysical parameters by receiving Earth’s surface reflected signals. The CYclone Global Navigation Satellite System (CYGNSS) mission with eight microsatellites launched by NASA in December 2016, which provides an unprecedented opportunity to rapidly acquire ocean surface wind speed globally. In this paper, a refined spaceborne GNSS-R sea surface wind speed retrieval algorithm is presented and validated with the ground surface reference wind speed from numerical weather prediction (NWP) and cross-calibrated multi-platform ocean surface wind vector analysis product (CCMP), respectively. The results show that when the wind speed was less than 20 m/s, the RMS of the GNSS-R retrieved wind could achieve 1.84 m/s in the case where the NWP winds were used as the ground truth winds, while the result was better than the NWP-based retrieved wind speed with an RMS of 1.68 m/s when the CCMP winds were used. The two sets of inversion results were further evaluated by the buoy winds, and the uncertainties from the NWP-derived and CCMP-derived model prediction wind speed were 1.91 m/s and 1.87 m/s, respectively. The accuracy of inversed wind speeds for different GNSS pseudo-random noise (PRN) satellites and types was also analyzed and presented, which showed similar for different PRN satellites and different types of satellites.

Systematic Scatterometer Wind Errors Near Coastal Mountains.

Satellite scatterometers provide the only regular observations of surface wind vectors over vast swaths of the world oceans, including coastal regions, which are of great scientific and societal interest but still present challenges for remote sensing. Here we demonstrate systematic scatterometer wind errors near Hawaii's Big Island: Two counter‐rotating lee vortices, which are clear in the International Comprehensive Ocean‐Atmosphere Data Set ship‐based wind climatology and in aircraft observations, are absent in the Jet Propulsion Laboratory and Remote Sensing Systems scatterometer wind climatologies. We demonstrate similar errors in the representation of transient Catalina Eddy events in the Southern California Bight. These errors likely arise from the nonuniqueness of scatterometer wind observations, that is, an “ambiguity removal” is required during processing to select from multiple wind solutions to the geophysical model function. We discuss strategies to improve the ambiguity selection near coastal mountains, where small‐scale wind reversals are common.

Tracking fishing ground parameters in cloudy region using ocean colour and satellite-derived surface flow estimates: A study in the Bay of Bengal

ABSTRACT A new conceptual framework, based on ocean bio-physical observations from different satellites, has been proposed to track fishing ground parameters to identify Potential Fishing Zones (PFZ) in the Bay of Bengal (BoB). The proposed technique also attempts to provide a short-term forecast based on feature propagation, even under cloudy conditions. The current study has been carried out to understand the link between possible fish catch availability and satellite-derived parameters such as chlorophyll concentration, sea surface temperature, sea-level anomaly, ocean surface currents and wind vectors. Net Ekman transport obtained from the upfront and downfront components of the wind relative to the frontal direction provides valuable information on the forecast of PFZ regions and its possible shift. Comparison of the identified PFZs with limited in situ fish catch data proves that the suggested approach holds the promise in improved monitoring of possible fish catch locations. The study provides a novel approach for the monitoring and short-term forecasting of PFZ even for cloud-contaminated regions by using all possible ocean information from space-based platforms.

The Performance of Dual-Frequency Polarimetric Scatterometer in Sea Surface Wind Retrieval

The wind retrieval performance of HY-2A scanning scatterometer operating at Ku-band in HH and VV polarizations has been well evaluated in the wind speed range of 0–25 ms−1. In order to obtain more accurate ocean wind field, a potential extension of dual-frequency (C-band and Ku-band) polarimetric measurements is investigated for both low and very high wind speeds, from 5 to 45ms−1. Based on the geophysical model functions of C-band and Ku-band, the simulation results show that the polarimetric measurements of Ku-band can improve the wind vector retrieval over the entire scatterometer swath, especially in nadir area, with the wind direction root-mean-square error (RMSE) less than 12° in the wind speed range of 5–25 m s−1. Furthermore, the results also show that C-band cross-polarization plays a very important role in improving the wind speed retrieval, with the wind speed retrieval accuracy better than 2 ms−1 for all wind conditions (0–45 ms−1). For extreme winds, the C-band HH backscatter coefficients modeled by CMOD5.N(H) and the ocean co-polarization ratio model at large incidence are used to retrieve sea surface wind vector. This result reveals that there is a big decrease of wind direction retrieval RMSE for extreme wind fields, and the retrieved result of C-band HH polarization is nearly the same as that of C-band VV polarization for low-to-high wind speed (5–25 ms−1). Thus, to improve the wind retrieval for all wind conditions, the dual-frequency polarimetric scatterometer with C-band and Ku-band horizontal polarization in inner beam, and C-band horizontal and Ku-band vertical polarization in outer beam, can be used to measure ocean winds. This study will contribute to the wind retrieval with merged satellites data and the future spaceborne scatterometer.

SEASTAR: A Mission to Study Ocean Submesoscale Dynamics and Small-Scale Atmosphere-Ocean Processes in Coastal, Shelf and Polar Seas

High-resolution satellite images of ocean color and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean mixing and ocean vertical transports, with advanced numerical models and in situ observations highlighting fundamental changes in dynamics when scales reach 1 km. Numerous scientific publications highlight the global impact of small oceanic scales on marine ecosystems, operational forecasts and long-term climate projections through strong ageostrophic circulations, large vertical ocean velocities and mixed layer re-stratification. Small-scale processes particularly dominate in coastal, shelf and polar seas where they mediate important exchanges between land, ocean, atmosphere and the cryosphere e.g. freshwater, pollutants. As numerical models continue to evolve towards finer spatial resolution and increasingly complex coupled atmosphere-wave-ice-ocean systems, modern observing capability lags behind, unable to deliver the high-resolution synoptic measurements of total currents, wind vectors and waves needed to advance understanding, develop better parameterizations and improve model validations, forecasts and projections. SEASTAR is a satellite mission concept that proposes to directly address this critical observational gap with synoptic two-dimensional imaging of total ocean surface current vectors and wind vectors at 1 km resolution and coincident directional wave spectra. Based on major recent advances in squinted along-track Synthetic Aperture Radar interferometry, SEASTAR is an innovative, mature concept with unique demonstrated capabilities, seeking to proceed towards spaceborne implementation within Europe and beyond.

Integrated Observations of Global Surface Winds, Currents, and Waves: Requirements and Challenges for the Next Decade

Ocean surface winds, currents, and waves play a crucial role in exchanges of momentum, energy, heat, freshwater, gases, and other tracers between the ocean, atmosphere, and ice. Despite surface waves being strongly coupled to the upper ocean circulation and the overlying atmosphere, efforts to improve ocean, atmospheric, and wave observations and models have evolved somewhat independently. From an observational point of view, community efforts to bridge this gap have led to proposals for satellite Doppler oceanography mission concepts, which could provide unprecedented measurements of absolute surface velocity and directional wave spectrum at global scales. This paper reviews the present state of observations of surface winds, currents, and waves, and it outlines observational gaps that limit our current understanding of coupled processes that happen at the air-sea-ice interface. A significant challenge for the coming decade of wind, current, and wave observations will come in combining and interpreting measurements from (a) wave-buoys and high-frequency radars in coastal regions, (b) surface drifters and wave-enabled drifters in the open-ocean, marginal ice zones, and wave-current interaction ``hot-spots'', and (c) simultaneous measurements of absolute surface currents, ocean surface wind vector, and directional wave spectrum from Doppler satellite sensors.

Inconsistencies in scatterometer wind products based on ASCAT and OSCAT-2 collocations

Sea surface vector winds from multiple satellite scatterometers are especially useful for oceanic and atmospheric applications. On the one hand, the number of space-borne scatterometers is increasing in recent years. On the other hand, the homogenization of wind products from different scatterometers and producers remains a challenge, which potentially prevents the beneficial use of multiple scatterometers for numerical weather prediction, studying air-sea interactions or monitoring and forecasting the ocean. In this study, the inconsistencies in scatterometer wind products are analyzed and differences are attributed to the different aspects of scatterometer wind measurements and processing in order to guide further research towards consistent scatterometer wind products. More in particular, the collocated C-band MetOp/ASCAT and Ku-band SCATSAT-1/OSCAT-2 data allow a unique opportunity for close and abundant global collocations of different scatterometer wind products. The Ku-band wind data are independently produced by the Royal Netherlands Meteorological Institute (KNMI) and the Jet Propulsion Laboratory (JPL). The comparison shows that the KNMI OSCAT-2 wind product rejects more “poor” quality data than the JPL wind product, while both quality control (QC) schemes have merits and may be combined in a future development. Furthermore, the JPL OSCAT-2 wind speeds differ generally more from the ASCAT winds than the KNMI OSCAT-2 winds, especially for wind speeds above 17 m/s. It is confirmed that the wind speed differences between C- and Ku-band scatterometers are mainly caused by the effect of Sea Surface Temperature (SST). While the wind direction characteristics of the OSCAT-2 wind products are closely related to the inversion algorithms used, the geophysical model function (GMF) used in the wind inversion is the dominant factor for the remarkable differences between OSCAT-2 wind speeds produced by KNMI and JPL. The error characteristics and inconsistencies of ASCAT and OSCAT-2 wind products presented in this manuscript provide guidance for data users and will promote further improvements in the consistency of scatterometer wind products.

A Perspective on the Performance of the CFOSAT Rotating Fan-Beam Scatterometer

The China-France Oceanography Satellite (CFOSAT) to be launched in October 2018 will carry two innovative payloads, i.e., the surface wave investigation and monitoring instrument and the rotating fan-beam scatterometer [CFOSAT scatterometer (CFOSCAT)]. Both instruments, operated in Ku-band microwave frequency, are dedicated to the measurement of sea surface wave spectra and wind vectors, respectively. This paper provides an overview of the system definition and characteristics of the CFOSCAT instrument. A prelaunch analysis is carried out to estimate the scatterometer backscatter and wind quality based on the developed CFOSCAT simulator prototype. The overall simulation includes two parts: first, a forward model is developed to simulate the ocean backscatter signals, accounting for both instrument and geophysical noise. Second, a wind inversion processor is used to retrieve wind vectors from the outputs of the forward model. The benefits and challenges of the novel observing geometries are addressed in terms of the CFOSCAT wind retrieval. The simulations show that the backscatter accuracy and the retrieved wind quality of CFOSCAT are quite promising and meet the CFOSAT mission requirements.