Flexas M. Mar

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M. Mar

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  • Article
    An observing system simulation experiment for the calibration and validation of the surface water ocean topography sea surface height measurement using in situ platforms
    (American Meteorological Society, 2018-02-07) Wang, Jinbo ; Fu, Lee-Lueng ; Qiu, Bo ; Menemenlis, Dimitris ; Farrar, J. Thomas ; Chao, Yi ; Thompson, Andrew F. ; Flexas, M. Mar
    The wavenumber spectrum of sea surface height (SSH) is an important indicator of the dynamics of the ocean interior. While the SSH wavenumber spectrum has been well studied at mesoscale wavelengths and longer, using both in situ oceanographic measurements and satellite altimetry, it remains largely unknown for wavelengths less than ~70 km. The Surface Water Ocean Topography (SWOT) satellite mission aims to resolve the SSH wavenumber spectrum at 15–150-km wavelengths, which is specified as one of the mission requirements. The mission calibration and validation (CalVal) requires the ground truth of a synoptic SSH field to resolve the targeted wavelengths, but no existing observational network is able to fulfill the task. A high-resolution global ocean simulation is used to conduct an observing system simulation experiment (OSSE) to identify the suitable oceanographic in situ measurements for SWOT SSH CalVal. After fixing 20 measuring locations (the minimum number for resolving 15–150-km wavelengths) along the SWOT swath, four instrument platforms were tested: pressure-sensor-equipped inverted echo sounders (PIES), underway conductivity–temperature–depth (UCTD) sensors, instrumented moorings, and underwater gliders. In the context of the OSSE, PIES was found to be an unsuitable tool for the target region and for SSH scales 15–70 km; the slowness of a single UCTD leads to significant aliasing by high-frequency motions at short wavelengths below ~30 km; an array of station-keeping gliders may meet the requirement; and an array of moorings is the most effective system among the four tested instruments for meeting the mission’s requirement. The results shown here warrant a prelaunch field campaign to further test the performance of station-keeping gliders.
  • Article
    Global estimates of the energy transfer from the wind to the ocean, with emphasis on near-inertial oscillations
    (American Geophysical Union, 2019-07-03) Flexas, M. Mar ; Thompson, Andrew F. ; Torres, Hector S. ; Klein, Patrice ; Farrar, J. Thomas ; Zhang, Hong ; Menemenlis, Dimitris
    Estimates of the kinetic energy transfer from the wind to the ocean are often limited by the spatial and temporal resolution of surface currents and surface winds. Here we examine the wind work in a pair of global, very high‐resolution (1/48° and 1/24°) MIT general circulation model simulations in Latitude‐Longitude‐polar Cap (LLC) configuration that provide hourly output at spatial resolutions of a few kilometers and include tidal forcing. A cospectrum analysis of wind stress and ocean surface currents shows positive contribution at large scales (>300 km) and near‐inertial frequency and negative contribution from mesoscales, tidal frequencies, and internal gravity waves. Larger surface kinetic energy fluxes are in the Kuroshio in winter at large scales (40 mW/m2) and mesoscales (−30 mW/m2). The Kerguelen region is dominated by large scale (∼20 mW/m2), followed by inertial oscillations in summer (13 mW/m2) and mesoscale in winter (−12 mW/m2). Kinetic energy fluxes from internal gravity waves (−0.1 to −9.9 mW/m2) are generally stronger in summer. Surface kinetic energy fluxes in the LLC simulations are 4.71 TW, which is 25–85% higher than previous global estimates from coarser (1/6–1/10°) general ocean circulation models; this is likely due to improved representation of wind variability (6‐hourly, 0.14°, operational European Center for Medium‐Range Weather Forecasts). However, the low wind power input to the near‐inertial frequency band obtained with LLC (0.16 TW) compared to global slab models suggests that wind variability on time scales less than 6 hr and spatial scales less than 15 km are critical to better representing the wind power input in ocean circulation models.
  • Article
    Satellites to seafloor : toward fully autonomous ocean sampling
    (Oceanography Society, 2017-06) Thompson, Andrew F. ; Chao, Yi ; Chien, Steve ; Kinsey, James C. ; Flexas, M. Mar ; Erickson, Zachary K. ; Farrara, John ; Fratantoni, David M. ; Branch, Andrew ; Chu, Selina ; Troesch, Martina ; Claus, Brian ; Kepper, James
    Future ocean observing systems will rely heavily on autonomous vehicles to achieve the persistent and heterogeneous measurements needed to understand the ocean’s impact on the climate system. The day-to-day maintenance of these arrays will become increasingly challenging if significant human resources, such as manual piloting, are required. For this reason, techniques need to be developed that permit autonomous determination of sampling directives based on science goals and responses to in situ, remote-sensing, and model-derived information. Techniques that can accommodate large arrays of assets and permit sustained observations of rapidly evolving ocean properties are especially needed for capturing interactions between physical circulation and biogeochemical cycling. Here we document the first field program of the Satellites to Seafloor project, designed to enable a closed loop of numerical model prediction, vehicle path-planning, in situ path implementation, data collection, and data assimilation for future model predictions. We present results from the first of two field programs carried out in Monterey Bay, California, over a period of three months in 2016. While relatively modest in scope, this approach provides a step toward an observing array that makes use of multiple information streams to update and improve sampling strategies without human intervention.