On the role of high frequency waves in ocean altimetry

This work mines a coastal and open ocean air-sea interaction field experiment data set where the goals are to refine satellite retrieval of wind, wind stress, and sea level using a microwave radar altimeter. The data were collected from a low-flying aircraft using a sensor suite designed to measure the surface waves, radar backscatter, the atmospheric flow, and turbulent fluxes within the marine boundary layer. This uncommon ensemble provides the means to address several specific altimeter-related topics. First, we examine and document the impact that non wind-driven gravity wave variability, e.g. swell, has upon the commonly-invoked direct relationship between altimeter backscatter and near surface wind speed. The demonstrated impact is larger in magnitude and more direct than previously suggested. The study also isolates the wind-dependence of short-scale slope variance and suggests its magnitude is somewhat lower than shown elsewhere while a second-order dependence on long waves is also evident. A second study assesses the hypothesis that wind-aligned swell interacts with the atmospheric boundary flow leading to a depressed level of turbulence. Cases of reduced drag coefficient at moderate wind speeds were in evidence within the data set, and buoy observations indicate that swell was present and a likely control during these events. Coincidentally, short-scale wave roughness was also depressed suggesting decreased wind stress. Attempts to confirm the theory failed, however, due to numerous limitations in the quantity and quality of the data in hand. A lesson learned is that decoupling atmospheric stability and wave impacts in field campaigns requires both a very large amount of data as well as vertical resolution of fluxes within the first 10--20 m of the surface

Impact of high frequency waves on the ocean altimeter range bias

New aircraft observations are presented on the range determination error in satellite altimetry associated with ocean waves. Laser-based measurements of the cross correlation between the gravity wave slope and elevation are reported for the first time. These observations provide direct access to a long, O(10 m), gravity wave statistic central to nonlinear wave theory prediction of the altimeter sea state bias. Coincident Ka-band radar scattering data are used to estimate an electromagnetic (EM) range bias analogous to that in satellite altimetry. These data, along with ancillary wind and wave slope variance estimates, are used alongside existing theory to evaluate the extent of long- versus short-wave, O(cm), control of the bias. The longer wave bias contribution to the total EM bias is shown to range from 25 to as much as 100%. Moreover, on average the term is linearly related to wind speed and to the gravity wave slope variance, consistent with WNL theory. The EM bias associated with interactions between long and short waves is obtained assuming the effect is additive to the independently observed long-wave factor. This second component is also a substantial contributor, is observed to be quadratic in wind speed or wave slope, and dominates at moderate wind speeds. The behavior is shown to be consistent with EM bias prediction based in hydrodynamic modulation theory. Study implications for improved correction of the on-orbit satellite sea state bias are discussed

Controls on buffering and coastal acidification in a temperate estuary

Estuaries may be uniquely susceptible to the combined acidification pressures of atmospherically driven ocean acidification (OA), biologically driven CO2 inputs from the estuary itself, and terrestrially derived freshwater inputs. This study utilized continuous measurements of total alkalinity (TA) and the partial pressure of carbon dioxide (pCO2) from the mouth of Great Bay, a temperate northeastern U.S. estuary, to examine the potential influences of endmember mixing and biogeochemical transformation upon estuary buffering capacity (β–H). Observations were collected hourly over 28 months representing all seasons between May 2016 and December 2019. Results indicated that endmember mixing explained most of the observed variability in TA and dissolved inorganic carbon (DIC), concentrations of which varied strongly with season. For much of the year, mixing dictated the relative proportions of salinity-normalized TA and DIC as well, but a fall season shift in these proportions indicated that aerobic respiration was observed, which would decrease β–H by decreasing TA and increasing DIC. However, fall was also the season of weakest statistical correspondence between salinity and both TA and DIC, as well as the overall highest salinity, TA and β–H. Potential biogeochemically driven β–H decreases were overshadowed by increased buffering capacity supplied by coastal ocean water. A simple modeling exercise showed that mixing processes controlled most monthly changes in TA and DIC, obscuring impacts from air–sea exchange or metabolic processes. Advective mixing contributions may be as important as biogeochemically driven changes to observe when evaluating local estuarine and coastal OA

Sea state bias in altimeter sea level estimates determined by combining wave model and satellite data

This study documents a method for increasing the precision of satellite-derived sea level measurements. Results are achieved using an enhanced three-dimensional (3-D) sea state bias (SSB) correction model derived from both Jason-1 altimeter ocean observations (i.e., sea state and wind) and estimates of mean wave period from a numerical ocean wave model, NOAA’s WAVEWATCH III. A multiyear evaluation of Jason-1 data indicates sea surface height variance reduction of 1.26 (±0.2) cm2 in comparison to the commonly applied two-parameter SSB model. The improvement is similar for two separate variance reduction metrics and for separate annual data sets spanning 2002–2004. Spatial evaluation of improvement shows skill increase at all latitudes. Results indicate the new model can reduce the total Jason-1 and Jason-2 altimeter range error budgets by 7.5%. In addition to the 2-D (two-dimensional) and 3-D model differences in correcting the range for wavefield variability, mean model regional differences also occur across the globe and indicate a possible 1–2 cm gradient across ocean basins linked to the zonal variation in wave period (short fetch and period in the west, swells and long period in the east). Overall success of this model provides first evidence that operational wave modeling can support improved ocean altimetry. Future efforts will attempt to work within the limits of wave modeling capabilities to maximize their benefit to Jason-1 and Jason-2 SSB correction methods

Flow distortion investigation of wind velocity perturbations for two ocean meteorological platforms

A computational fluid dynamics (CFD) study was performed of the wind flow around two ocean buoys used to collect meteorological data from sensors mounted on the buoy tower. The CFD approach allowed wind velocity perturbations to be evaluated as a step towards quantifying the impacts of flow distortion on buoy wind measurements. The two buoys evaluated were the Wood Hole Oceanographic Institution WHOI Modular Ocean Buoy System and the University of New Hampshire (UNH) 2.1 m discus buoy. Engineering drawings were used to create a computational mesh for each buoy. Suitable solution methods were then developed and tested, CFD simulations were performed, and the results evaluated. Eleven CFD runs were performed, six for the WHOI buoy and five for the UNH buoy. Highlights of analysis for the WHOI buoy were that horizontal flow distortion was relatively small (<1%) for head-on flow, but that the tendency of the buoy to establish an angle of about 30 degrees relative to the flow resulted in acceleration at one anemometer location and deceleration at the other. Highlights of the analysis for the UNH buoy were that flow distortion of about 5% at the wind sensor location could be cut by about a factor of two by either raising the sensor by 2 ft or removing solar panels.Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA17RJ1223 for the Cooperative Institute for Climate and Ocean Research (CICOR)

Temporal and spatial dynamics of CO2 air-sea flux in the Gulf of Maine

Ocean surface layer carbon dioxide (CO2) data collected in the Gulf of Maine from 2004 to 2008 are presented. Monthly shipboard observations are combined with additional higher‐resolution CO2 observations to characterize CO2 fugacity ( fCO2) and CO2 flux over hourly to interannual time scales. Observed fCO2 andCO2 flux dynamics are dominated by a seasonal cycle, with a large spring influx of CO2 and a fall‐to‐winter efflux back to the atmosphere. The temporal results at inner, middle, and outer shelf locations are highly correlated, and observed spatial variability is generally small relative to the monthly to seasonal temporal changes. The averaged annual flux is in near balance and is a net source of carbon to the atmosphere over 5 years, with a value of +0.38 mol m−2 yr−1. However, moderate interannual variation is also observed, where years 2005 and 2007 represent cases of regional source (+0.71) and sink (−0.11) anomalies. We use moored daily CO2 measurements to quantify aliasing due to temporal undersampling, an important error budget term that is typically unresolved. The uncertainty of our derived annual flux measurement is ±0.26 mol m−2 yr−1 and is dominated by this aliasing term. Comparison of results to the neighboring Middle and South Atlantic Bight coastal shelf systems indicates that the Gulf of Maine exhibits a similar annual cycle and range of oceanic fCO2 magnitude but differs in the seasonal phase. It also differs by enhanced fCO2 controls by factors other than temperature‐driven solubility, including biological drawdown, fall‐to‐winter vertical mixing, and river runoff

Variability of USA East Coast surface total alkalinity distributions revealed by automated instrument measurements

Seawater total alkalinity (TA) is one important determinant used to monitor the ocean carbon cycle, whose spatial distributions have previously been characterized along the United States East Coast via discrete bottle samples. Using these data, several regional models for TA retrievals based on practical salinity (S) have been developed. Broad-scale seasonal or interannual variations, however, are not well resolved in these models and existing data are highly seasonally biased. This study reports findings from the first long duration deployment of a new, commercially available TA titrator aboard a research vessel and the continuous underway surface TA measurements produced. The instrument, operated on seven East Coast USA cruises during six months in 2017 and for two months in 2018 on the summertime East Coast Ocean Acidification survey (ECOA-2), collected a total of nearly 11,000 surface TA measurements. Data from these efforts, along with a newly synthesized set of more than 11,000 regional surface TA observations, are analyzed to re-examine distributions of TA and S along the United States East Coast. Overall, regional distributions of S and TA generally agreed with prior findings, but linear TA:S regressions varied markedly over time and deviated from previously developed models. This variability is likely due to a combination of biological, seasonal, and episodic influences and indicates that substantial errors of ±10–20 μmol kg−1 in TA estimation from S can be expected due to these factors. This finding has likely implications for numerical ecosystem modeling and inorganic carbon system calculations. New results presented in this paper provide refined surface TA:S relationships, present more data in space and time, and improve TA modeling uncertainty

Momentum transfer over the coastal zone

Spatial variations of surface stress over the coastal shoaling zone are studied offshore of Duck, North Carolina, by the LongEZ research aircraft, equipped to measure both atmospheric turbulence and oceanic waves. We find that the spatial variation of the friction velocity with offshore distance is much larger with offshore flow than with onshore flow. In general, the mean square slope of the short waves (wavelength shorter than 2 m) decreases with offshore distance, while the mean square slope of the long waves (wavelength longer than 2 m) increases with offshore distance. With onshore flow the friction velocity is strongly correlated with surface waves. In addition, the variation of the neutral drag coefficient is well correlated with the atmospheric bulk Richardson number. With offshore flow the observed momentum flux significantly decreases with offshore distance. Within the first few kilometer offshore, the relationship between the friction velocity and the mean square slope of the short waves and the relationship between the neutral drag coefficient and the atmospheric bulk Richardson number are obscured by the direct influence of the upstream land surface on the measured turbulence. These relationships for offshore flow agree well with those for onshore flow if the fetch is beyond the immediate influence of the land surface. The results in this study suggests that the effects of the strong turbulence advected from over the nearby land surface in offshore flow may lead to ambiguous physical interpretation of the correlation between the momentum flux and the wave state

Using present-day observations to detect when anthropogenic change forces surface ocean carbonate chemistry outside preindustrial bounds

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 13 (2016): 5065-5083, doi:10.5194/bg-13-5065-2016.One of the major challenges to assessing the impact of ocean acidification on marine life is detecting and interpreting long-term change in the context of natural variability. This study addresses this need through a global synthesis of monthly pH and aragonite saturation state (Ωarag) climatologies for 12 open ocean, coastal, and coral reef locations using 3-hourly moored observations of surface seawater partial pressure of CO2 and pH collected together since as early as 2010. Mooring observations suggest open ocean subtropical and subarctic sites experience present-day surface pH and Ωarag conditions outside the bounds of preindustrial variability throughout most, if not all, of the year. In general, coastal mooring sites experience more natural variability and thus, more overlap with preindustrial conditions; however, present-day Ωarag conditions surpass biologically relevant thresholds associated with ocean acidification impacts on Mytilus californianus (Ωarag < 1.8) and Crassostrea gigas (Ωarag < 2.0) larvae in the California Current Ecosystem (CCE) and Mya arenaria larvae in the Gulf of Maine (Ωarag < 1.6). At the most variable mooring locations in coastal systems of the CCE, subseasonal conditions approached Ωarag =  1. Global and regional models and data syntheses of ship-based observations tended to underestimate seasonal variability compared to mooring observations. Efforts such as this to characterize all patterns of pH and Ωarag variability and change at key locations are fundamental to assessing present-day biological impacts of ocean acidification, further improving experimental design to interrogate organism response under real-world conditions, and improving predictive models and vulnerability assessments seeking to quantify the broader impacts of ocean acidification.The CO2 and ocean acidification observations were funded by NOAA’s Climate Observation Division (COD) in the Climate Program Office and NOAA’s Ocean Acidification Program. The maintenance of the Stratus and WHOTS Ocean Reference Stations were also supported by NOAA COD (NA09OAR4320129). Additional support for buoy equipment, maintenance, and/or ancillary measurements was provided by NOAA through the US Integrated Ocean Observing System office: for the La Parguera buoy under a Cooperative Agreement (NA11NOS0120035) with the Caribbean Coastal Ocean Observing System, for the Chá b˘a buoy under a Cooperative Agreement (NA11NOS0120036) with the Northwest Association of Networked Ocean Observing System, for the Gray’s Reef buoy under a Cooperative Agreement (NA11NOS0120033) with the Southeast Coastal Ocean Observing Regional Association, and for the Gulf of Main buoy under a Cooperative Agreement (NA11NOS0120034) with the Northeastern Regional Association of Coastal and Ocean Observing Systems

Super sites for advancing understanding of the oceanic and atmospheric boundary layers

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Clayson, C. A., Centurioni, L., Cronin, M. F., Edson, J., Gille, S., Muller-Karger, F., Parfitt, R., Riihimaki, L. D., Smith, S. R., Swart, S., Vandemark, D., Boas, A. B. V., Zappa, C. J., & Zhang, D. Super sites for advancing understanding of the oceanic and atmospheric boundary layers. Marine Technology Society Journal, 55(3), (2021): 144–145, https://doi.org/10.4031/MTSJ.55.3.11.Air‐sea interactions are critical to large-scale weather and climate predictions because of the ocean's ability to absorb excess atmospheric heat and carbon and regulate exchanges of momentum, water vapor, and other greenhouse gases. These exchanges are controlled by molecular, turbulent, and wave-driven processes in the atmospheric and oceanic boundary layers. Improved understanding and representation of these processes in models are key for increasing Earth system prediction skill, particularly for subseasonal to decadal time scales. Our understanding and ability to model these processes within this coupled system is presently inadequate due in large part to a lack of data: contemporaneous long-term observations from the top of the marine atmospheric boundary layer (MABL) to the base of the oceanic mixing layer. We propose the concept of “Super Sites” to provide multi-year suites of measurements at specific locations to simultaneously characterize physical and biogeochemical processes within the coupled boundary layers at high spatial and temporal resolution. Measurements will be made from floating platforms, buoys, towers, and autonomous vehicles, utilizing both in-situ and remote sensors. The engineering challenges and level of coordination, integration, and interoperability required to develop these coupled ocean‐atmosphere Super Sites place them in an “Ocean Shot” class.NOAA CVP TPOS, Understanding Processes Controlling Near-Surface Salinity in the Tropical Ocean Using Multiscale Coupled Modeling and Analysis, NA18OAR4310402 to CAC and JE. NSF Award PLR-1425989 and OPP-1936222, Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) to SG. NOAA, BOEM, ONR, NSF, NOPP, NASA Applied Sciences Office, Biodiversity & Ecological Forecasting Program; National Science Foundation (Co-PI J. Pearlman); OceanObs Research Coordination Network (OCE-1728913) to FM-K. NASA, SWOT program, Award # 80NSSC20K1136 to ABVB. NSF, Investigating the Air-Sea Energy Exchange in the presence of Surface Gravity Waves by Measurements of Turbulence Dissipation, Production and Transport, OCE 17-56839; NSF, A Multi-Spectral Thermal Infrared Imaging System for Air-Sea Interaction Research, OCE 20-23678; NSF, Investigating the Relationship Between Ocean Surface Gravity–Capillary Waves, Surface-Layer Hydrodynamics, and Air–Sea Momentum Flux, OCE 20-49579 to CJZ. Partially funded by NOAA/Climate Program Office and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 to DZ