Wortham Cimarron J. L.

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Wortham
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Cimarron J. L.
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  • Article
    Eddy stirring and horizontal diffusivity from Argo float observations : geographic and depth variability
    (John Wiley & Sons, 2015-05-21) Cole, Sylvia T. ; Wortham, Cimarron J. L. ; Kunze, Eric ; Owens, W. Brechner
    Stirring along isopycnals is a significant factor in determining the distribution of tracers within the ocean. Salinity anomalies on density surfaces from Argo float profiles are used to investigate horizontal stirring and estimate eddy mixing lengths. Eddy mixing length and velocity fluctuations from the ECCO2 global state estimate are used to estimate horizontal diffusivity at a 300 km scale in the upper 2000 m with near-global coverage. Diffusivity varies by over two orders of magnitude with latitude, longitude, and depth. In all basins, diffusivity is elevated in zonal bands corresponding to strong current regions, including western boundary current extension regions, the Antarctic Circumpolar Current, and equatorial current systems. The estimated mixing lengths and diffusivities provide an observationally based data set that can be used to test and constrain predictions and parameterizations of eddy stirring.
  • Thesis
    A multi-dimensional spectral description of ocean variability with applications
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2013-02) Wortham, Cimarron J. L.
    Efforts to monitor the ocean for signs of climate change are hampered by ever-present noise, in the form of stochastic ocean variability, and detailed knowledge of the character of this noise is necessary for estimating the significance of apparent trends. Typically, uncertainty estimates are made by a variety of ad hoc methods, often based on numerical model results or the variability of the data set being analyzed. We provide a systematic approach based on the four-dimensional frequency-wavenumber spectrum of low-frequency ocean variability. This thesis presents an empirical model of the spectrum of ocean variability for periods between about 20 days and 15 years and wavelengths of about 200{10,000 km, and describes applications to ocean circulation trend detection, observing system design, and satellite data processing. The horizontal wavenumber-frequency part of the model spectrum is based on satellite altimetry, current meter data, moored temperature records, and shipboard ADCP data. The spectrum is dominated by motions along a "nondispersive line". The observations considered are consistent with a universal ω-2 power law at the high end of the frequency range, but inconsistent with a universal wavenumber power law. The model spectrum is globally varying and accounts for changes in dominant phase speed, period, and wavelength with location. The vertical structure of the model spectrum is based on numerical model results, current meter data, and theoretical considerations. We find that the vertical structure of kinetic energy is surface intensified relative to the simplest theoretical predictions. We present a theory for the interaction of linear Rossby waves with rough topography; rough topography can explain both the observed phase speeds and vertical structure of variability. The improved description of low-frequency ocean variability presented here will serve as a useful tool for future oceanographic studies.
  • Dataset
    Eddy diffusivity from Argo temperature and salinity profiles
    ( 2018-04-10) Cole, Sylvia T. ; Wortham, Cimarron J. L. ; Kunze, Eric ; Owens, W. Brechner
    Argo temperature and salinity profiles are combined with ECCO-2 velocity profiles to estimate eddy diffusivity in the upper 2000 m of the global ocean. The dataset includes relevant intermediate parameters (mixing length, salinity standard deviation, salinity gradient, velocity standard deviation) in addition to eddy diffusivity. The dataset is available using 1° or 3° bins.