Fofonoff Nicholas P.

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Nicholas P.
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  • Technical Report
    Available potential energy for mode eddies
    (Woods Hole Oceanographic Institution, 1981-07) Bray, Nancy Amanda ; Fofonoff, Nicholas P.
    Available potential energy (APE) is defined as the difference between total potential plus internal energy of a fluid in a gravity field and a corresponding reference field in which the fluid is redistributed (leveled) adiabatically to have constant stably-stratified densities along geopotential surfaces. Potential energy changes result from local shifts of flu id mass relative to geopotential surfaces that are accompanied by local changes of enthalpy and internal energy and global shifts of mass (because volumes of fluid elements are not conserved) that do not change enthalpy or internal energy. The potential energy changes are examined separately by computing available gravitational potential energy (GPE) per unit mass and total GPE (TGPE) per unit area. A technique for estimating GPE in the ocean is developed by introducirtg a reference density field (or an equivalent specific volume anomaly field) that is a function of pressure only and is connected to the observed field by adiabatic vertical displacements. The full empirical equation of state for seawater is used in the computational algorithm. The accuracy of the estimate is limited by the data and sampling and not by the algorithm itself, which can be made as precise as desired. The reference density field defined locally for an ocean region allows redefinition of dynamic height ΔD (potential energy per unit mass) relative to the reference field. TGPE per unit area becomes simply the horizontal average of dynamic height integrated over depth in the region considered. The reference density surfaces provide a precise approximation to material surfaces for tracing conservative variables such as salinity and potential temperature and for estimating vortex stretching between surfaces. The procedure is applied to the MODE density data collected in 1973. For each group of stations within five 2-week time windows (designated Groups A-E) the estimated GPE is compared with the net APE based on the Boussinesq approximation and to the low-frequency kinetic energy measured from moored buoys. Changes of potential energy of the reference field from one time window to the next are large compared with the GPE within each window, indicating the presence of scales larger than the station grid. An analysis of errors has been made to show the sensitivity of the estimates to data accuracy and sampling frequency.
  • Technical Report
    A compilation of moored current meter observations : volume I
    (Woods Hole Oceanographic Institution, 1965-08) Webster, Ferris ; Fofonoff, Nicholas P.
    Summaries of current measurements made with Richardson current meters at three moored stations in the Western North Atlantic are presented. Averaged quantities are presented in the form of computer-plotted curves.
  • Technical Report
    W.H.O.I./Brown CTD microprofiler : methods of calibration and data handling
    (Woods Hole Oceanographic Institution, 1974-12) Fofonoff, Nicholas P. ; Hayes, S. P. ; Millard, Robert C.
    This report describes calibration techniques developed over the past three years for the WHOI/Brown CTD in the Moored Array Program. Comparison is made with classical methods of hydrography for stations obtained in the MODE-1 density program. Methods for temperature lag correction and conversion of conductivity to salinity are given.
  • Technical Report
    A compilation of moored current meter observations volume III
    (Woods Hole Oceanographic Institution, 1967-11) Webster, Ferris ; Fofonoff, Nicholas P.
    Summaries of current measurements made with Richardson current meters in two regions of the Western North Atlantic are presented. Averaged quantities are presented in the form of computer-plotted curves.
  • Technical Report
    Current measurements from moored buoys
    (Woods Hole Oceanographic Institution, 1968-03) Fofonoff, Nicholas P.
    Since January 1965,a program has been underway at the Woods Hole Oceanographic Institution, to measure currents at a limited number of fixed sites on a year round basis. Initially, one site was instrumented with both surface and subsurface moorings. The program has now been expanded to 4 major sites, extending along 70°W, from 39°20 ' N to the Hatteras Abyssal Plain at 30°N . In nearly three years of operation, a total of 65 moorings have been placed at the working sites, for periods up to six months. Recoveries from these sites have provided many velocity records of excellent quality. The repetitive exposure of moorings of essentially similar design under relatively standardized conditions has served to define clearly the design and operational problems that are inherent in such a program. A brief account is given of some of the problems encountered in routine buoy setting operations, and some of the results obtained from the measurements.
  • Working Paper
    Algorithms for computation of fundamental properties of seawater
    (Unesco, 1983) Fofonoff, Nicholas P. ; Millard, Robert C.
    Algorithms for computation of fundamental properties of seawater, based on the practical salinity scale (PSS-78) and the international equation of state for seawater (EOS-80), are compiled in the present report for implementing and standardizing computer programs for oceanographic data processing. Sample FORTRAN subprograms and tables are given to illustrate usage of the algorithms and to show the range of variation and limits of validity of commonly used seawater properties within the oceanic ranges for salinity, temperature and pressure. The algorithms cover the following: conductivity to salinity conversion; salinity to conductivity conversion; specific volume anomaly and density anomaly of seawater; pressure to depth conversion; freezing point temperature of seawater; specific heat of seawater; adiabatic lapse rate; potential temperature; sound speed in seawater.
  • Technical Report
    A compilation of moored current meter observations volume II
    (Woods Hole Oceanographic Institution, 1966-11) Webster, Ferris ; Fofonoff, Nicholas P.
    Summaries of current measurements made with Richardson current meters at a group of moored stations near Bermuda, and at a single station south of Bermuda are presented. Averaged quantities are presented in the form of computer-plotted curves.
  • Technical Report
    Report on R. V. Akademik Vernadsky cruise 39, stage IV, June 17 - July 17, 1989
    (Woods Hole Oceanographic Institution, 1990-04) Fofonoff, Nicholas P. ; Levy, Ellen ; Kettle, A. James ; Navitsky, Richard C.
    Participation by U. S. personnel on Cruise 39, Leg IV (June 17 - July 17, 1989) of the Marine Hydrophysical Institute's research vessel Akademik Vernadsky provided valuable information, documented in the present report for planning future cooperative projects with Soviet oceanographers. Detailed descriptions are given of the ship, its scientific laboratories, computers and onboard instrumentation. Planning and operating procedures are described and examples are given of daily work plans, seminars, menus and social activities. Personal accounts by the U. S. participants are also included. Many of the shipboard activities were recorded on VHS video cassettes. The oceanographic data collected in the Gulf Stream survey region during Leg IV are documented in the report. Copies of data sets were provided to the U. S. participants in exchange for U. S. data from the region during the survey period.
  • Technical Report
    Horizontal divergence and vorticity estimates from velocity and temperature measurements in the MODE region
    (Woods Hole Oceanographic Institution, 1977-11) Bryden, Harry L. ; Fofonoff, Nicholas P.
    Estimates of horizontal derivatives of velocity made by differencing velocity measurements are used to show that the observed velocity field due to low-frequency mesoscale motions during the preliminary MidOcean Dynamics Experiment (MODE-0) field program is horizontally nondivergent within estimated errors. The errors in horizontal derivatives of 0.15 X lQ-6 s-1 are too large for direct estimates of horizontal divergence to be made accurately. The vorticity, however, can be estimated from these horizontal derivatives with an error small compared with its magnitude. Over the measurement period of SO days, the advection of planetary vorticity balances only one-half of the local change of vorticity so these observations cannot be explained in terms of barotropic Rossby waves alone. There are indications that vortex stretching, estimated from a linear heat balance, may balance the remaining local change of vorticity as expected for baroclinic Rossby waves. Based on other measurements in this region; however, it is likely that the horizontal advection of relative vorticity is also important in the vorticity balance. A positive, but not significantly different from zero, correlation between estimates of relative vorticity and advection of planetary vorticity suggests that the ens trophy of the observed velocity field is decreasing with time. In conjunction with a similar result for the perturbation potential energy obtained in this region, this result supports the view that the MODE region is a region of decay, rather than growth, of the low-frequency mesoscale motions.