Sebastien P. Bigorre

On the Exchange of Momentum over the Open Ocean

AbstractThis study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s−1) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m−1 ...

A Surface Mooring for Air–Sea Interaction Research in the Gulf Stream. Part II: Analysis of the Observations and Their Accuracies

AbstractA surface mooring was deployed in the Gulf Stream for 15 months to investigate the role of air–sea interaction in mode water formation and other processes. The accuracies of the near-surface meteorological and oceanographic measurements are investigated. In addition, the impacts of these measurement errors on the estimation and study of the air–sea fluxes in the Gulf Stream are discussed. Pre- and postdeployment calibrations together with in situ comparison between shipboard and moored sensors supported the identification of biases due to sensor drifts, sensor electronics, and calibration errors. A postdeployment field study was used to further investigate the performance of the wind sensors. The use of redundant sensor sets not only supported the filling of data gaps but also allowed an examination of the contribution of random errors. Air–sea fluxes were also analyzed and computed from both Coupled Ocean–Atmosphere Response Experiment (COARE) bulk parameterization and using direct covariance mea...

Eddies and an extreme water mass anomaly observed in the eastern south Pacific at the Stratus mooring

In the tropical eastern South Pacific the Stratus Ocean Reference Station (ORS) (∼20°S, 85.5°W) is located in the transition zone between the oxygen minimum zone (OMZ) and the well-oxygenated subtropical gyre. In February/March 2012, extremely anomalous water mass properties were observed in the thermocline at the Stratus ORS. The available eddy oxygen anomaly was −10.5 × 1016 µmol. This anomalous water was contained in an anticyclonic mode-water eddy crossing the mooring site. This eddy was absorbed at that time by an anticyclonic feature located south of the Stratus mooring. This was the largest water property anomaly observed at the mooring during the 13.5 month deployment period. The sea surface height anomaly (SSHA) of the strong mode-water eddy in February/March 2012 was weak, and while the lowest and highest SSHA were related to weak eddies, SSHA is found not to be sufficient to specify the eddy strength for subsurface-intensified eddies. Still, the anticyclonic eddy, and its related water mass characteristics, could be tracked backward in time in SSHA satellite data to a formation region in April 2011 off the Chilean coast. The resulting mean westward propagation velocity was 5.5 cm s−1. This extremely long-lived eddy carried the water characteristics from the near-coastal Chilean water to the open ocean. The water mass stayed isolated during the 11 month travel time due to high rotational speed of about 20 cm s−1 leading to almost zero oxygen in the subsurface layer of the anticyclonic mode-water eddy with indications of high primary production just below the mixed layer.

EUREC 4 A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.

Making progress and Wanting More: One-year near-surface current measurements from a surface mooring in the Gulf Stream and other thoughts about long-term surface moorings

Recently, as part of the CLIMODE (CLIVAR Mode Water Dynamics Experiment) a surface mooring was placed at 38degN, 65degW, a location that was at times in the core of the Gulf Stream. The surface mooring survived the first year at this 5000 m deep site, and the second deployment failed after 2 months. Two Nortek current meters provide some of the first direct near-surface current time series from such a location, and represent progress in sustained sampling from surface moorings. At the same time, the ability to sustain surface moorings for a year at a time presents challenges for current meters. After one year, it is hard to escape biofouling and, at times, damage from fishing gear. Such concerns lead to using current meters with no moving parts, but the present trade off between sampling and power in most instruments typically constrains one to four samples per hour, not frequent enough to either match the sustained sampling rate of temperature and salinity now possible or to resolve high frequency processes of interest. Once per minute sampling and proven accuracy as can be obtained by a Vector Measuring Current Meter (VMCM) would be desirable for near-surface moored deployments.

Sensor Performance and Data Quality Control

This chapter discusses the optimization of meteorological and oceanographic measurements from ocean surface moorings. First, we give guidelines and procedures for the selection of appropriate instruments and their preparation (calibration, configuration, integration and testing). Then, we present critical steps to evaluate and improve the data quality. We also discuss the limitations and benefits of real-time data, including various data quality control steps. Finally, we briefly compare two commonly used telemetry systems – ARGOS and Iridium.

NTAS 16 sixteenth setting of the NTAS Ocean Reference Station cruise on board RV Endeavor January 21 - February 8, 2017 Narragansett, Rhode Island - San Juan, Puerto Rico

Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA14OAR4320158.

Stratus 15 fifteenth setting of the Stratus Ocean Reference Station cruise on board RV Cabo de Hornos June 15 – 29, 2016 Valparaiso, Chile – Valparaiso, Chile

Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA14OAR4320158

UCTD and EM/APEX measurements in support of the April 2015 AirSWOT Campaign : cruise and data report

This work was performed for the Jet Propulsion Laboratory, California Institute of Technology, sponsored by the United States Government under the prime Contract NNN12AA01C between the Caltech and NASA under subcontract number 1523706. Farrar and Girton were also supported by NASA Grants NNX13AD90G.

Stratus 14 : fourteenth setting of the Stratus Ocean Reference Station cruise on board RV Cabo de Hornos April 14 - 30, 2015 Valparaiso, Chile

Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA140AR4320158