Flament Pierre J.

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Flament
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Pierre J.
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  • Article
    Horizontal stirring over the Northeast U.S. Continental Shelf: the spatial and temporal evolution of surface eddy kinetic energy
    (American Geophysical Union, 2022-05-21) Kirincich, Anthony R. ; Hodges, Benjamin A. ; Flament, Pierre J. ; Futch, Victoria
    This study examines the spatial and temporal variability of eddy kinetic energy over the Northeast Shelf using observations of surface currents from a unique array of six high frequency radar systems. Collected during summer and winter conditions over three consecutive years, the horizontal scales present were examined in the context of local wind and hydrographic variability, which were sampled concurrently from moorings and autonomous surface vehicles. While area-averaged mean kinetic energy at the surface was tightly coupled to wind forcing, eddy kinetic energy was not, and was lower in magnitude in winter than summer in all areas. Kinetic energy wavenumber spectral slopes were generally near k−5/3, but varied seasonally, spatially, and between years. In contrast, wavenumber spectra of surface temperature and salinity along repeat transect lines had sharp k−3 spectral slopes with little seasonal or inter-annual variability. Radar-based estimates of spectral kinetic energy fluxes revealed a mean transition scale of energy near 18 km during stratified months, but suggested much longer scales during winter. Overall, eddy kinetic energy was unrelated to local winds, but the up- or down-scale flux of kinetic energy was tied to wind events and, more weakly, to local density gradients.
  • Technical Report
    Altimeter processing tools for analyzing mesoscale ocean features
    (Woods Hole Oceanographic Institution, 1990-09) Caruso, Michael J. ; Sirkes, Ziv ; Flament, Pierre J. ; Baker, M. K.
    Satellite altimeters provide many opportunities for oceanographers to supplement their research with a valuable new data set. The recent GEOSAT exact repeat mission is the first of several altimeter missions proposed during the next decade. To utilize this new data, a software package was developed at the Woods Hole Oceanographic Institution and the University of Hawaii to facilitate the extraction of useful information from the NODC distributed GEOSAT data tapes. This software package was written with portability and modularity in mind. It should be possible to use this package with little or no modifications on data from future altimeters. The code was written in C and tested on Sun workstations and is oriented toward UNIX operating systems. However, since standard code was used, the programs should port easily to other computer systems. The modularity of the code should enable users to create additional programs. Additional programs designed to handle collocated water vapor corrections are also included for comparison.
  • Article
    Improving surface current resolution using direction finding algorithms for multiantenna high-frequency radars
    (American Meteorological Society, 2019-10-11) Kirincich, Anthony R. ; Emery, Brian ; Washburn, Libe ; Flament, Pierre J.
    While land-based high-frequency (HF) radars are the only instruments capable of resolving both the temporal and spatial variability of surface currents in the coastal ocean, recent high-resolution views suggest that the coastal ocean is more complex than presently deployed radar systems are able to reveal. This work uses a hybrid system, having elements of both phased arrays and direction finding radars, to improve the azimuthal resolution of HF radars. Data from two radars deployed along the U.S. East Coast and configured as 8-antenna grid arrays were used to evaluate potential direction finding and signal, or emitter, detection methods. Direction finding methods such as maximum likelihood estimation generally performed better than the well-known multiple signal classification (MUSIC) method given identical emitter detection methods. However, accurately estimating the number of emitters present in HF radar observations is a challenge. As MUSIC’s direction-of-arrival (DOA) function permits simple empirical tests that dramatically aid the detection process, MUSIC was found to be the superior method in this study. The 8-antenna arrays were able to provide more accurate estimates of MUSIC’s noise subspace than typical 3-antenna systems, eliminating the need for a series of empirical parameters to control MUSIC’s performance. Code developed for this research has been made available in an online repository.
  • Dataset
    Horizontal Stirring over the Northeast U.S. Continental Shelf: the Spatial and Temporal Evolution of Surface Eddy Kinetic Energy
    (Woods Hole Oceanographic Institution, 2021-09-30) Kirincich, Anthony R. ; Flament, Pierre J. ; Futch, Victoria ; Hodges, Benjamin A.
    This data was collected by Kirincich as part of the Submesoscale Dynamics Over The Shelf Study, with field observations in 2018 and 2019, as well as the HFR_winds project with field work in 2020. The analysis products presented were used to examine the space and time scales of eddy kinetic energy over the wide, shallow, NES continental shelf using a novel implementation of HFR to achieve spatial and temporal resolutions sufficient to capture the horizontal scales of velocity variability. The data consists of estimates of the near-surface horizontal (East and North) ocean currents made via High Frequency (HF) radar-based remote sensing of the Ocean backscatter spectrum as well as in situ moored hydrographic, velocity, and surface winds, and mobile surface hydrographic observations collected via autonomous vehicles. Data were collected within three separate measurement periods: July to December 2018, July to December 2019, and October to December 2020.