Armi Laurence

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Armi
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Laurence
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  • Technical Report
    Some evidence for boundary mixing in the deep ocean
    (Woods Hole Oceanographic Institution, 1979-01) Armi, Laurence
    Profiles of salinity and potential temperature in the deep ocean are presented which suggest the characteristic signature of two complementary mixing processes: vertical mixing within ~50-m-thick layers at boundaries and topographic features and lateral advection and eventual smearing of these mixed layers along iopycnal surfaces. The combined effect of these two processes is often parametrically disguised as a vertical eddy diffusivity in one-dimensional models. An estimate shows that the two processes can account for all the vertical mixing in the deep ocean without any vertical diffusion in the interior.
  • Technical Report
    The benthic boundary layer experiment on the Hatteras Abyssal Plain : current and temperature observations
    (Woods Hole Oceanographic Institution, 1981-02) Spencer, Ann ; D'Asaro, Eric A. ; Armi, Laurence
    The near bottom density and velocity fields above the Hatteras abyssal plain were observed with a current/temperature measuring array and a towed-yo-yoing profiler. This report describes the array data and includes details of calibration and data quality. Sources of direction error were diagnosed from vane and compass performance and bearing direction .
  • Technical Report
    The dynamics of the bottom boundary layer of the deep ocean
    (Woods Hole Oceanographic Institution, 1978-04) Armi, Laurence
    Profiles of salinity and temperature from the center of the Hatteras Abyssal Plain have a signature that is characteristic of mixing up a uniformly stratified region: a well-mixed layer above the bottom, bounded by an interface. The penetration height of the mixed-layer varies from about 10 m to 100 m and has been correlated by Armi and Millard (1976) with the one day mean velocity, inferred from current meters located above the bottom boundary layer. Here the dynamics of such layers is discussed. A model of entrainment and mixing for a flat bottom boundary layer is outlined; this model is however incomplete because we find too little known of the structure of turbulence above an Ekman layer. An alternate model is suggested by the estimate, from the correlation of penetration height with velocity of the internal Froude number of the mixed layer, F~1.7. This value indicates that the large penetration height may be due to the instability of the well-mixed layer to the formation of roll waves.
  • Technical Report
    SOFAR float Mediterranean outflow experiment data from the second year, 1985-86
    (Woods Hole Oceanographic Institution, 1988-09) Zemanovic, Marguerite E. ; Richardson, Philip L. ; Valdes, James R. ; Price, James F. ; Armi, Laurence
    In October, 1984, the Woods Hole Oceanographic Institution SOFAR float group began a three-year-long field program to observe the low frequency currents in the Canary Basin. The principal scientific goal was to learn how advection and diffusion by these currents determine the shape and amplitude of the Mediterranean salt tongue. Fourteen floats were launched at a depth of 1100 min a cluster centered on 32°N, 24°W, and seven other floats were launched incoherently along a north/south line from 24°N to 37°N. At the same time investigators from Scripps Institution of Oceanography and the University of Rhode Island used four other SOFAR floats to tag a Meddy, a submesoscale lens of Mediterranean water. In October, 1985, seven additional floats were launched, four in three different Meddies, one of which was tracked during year 1. This report describes the second year of the floats launched in 1984 and the first year of the ones launched in 1985. Approximately 41 years of float trajectories were produced during the first two years of the experiment. One of the striking accomplishments is the successful tracking of one Meddy over two full years plus the tracking of two other Meddies during the second year.
  • Technical Report
    Flow structures of the benthic ocean
    (Woods Hole Oceanographic Institution, 1980-11) Armi, Laurence ; D'Asaro, Eric A.
    Three-dimensional structure of the near-bottom density field was observed with a towed yo-yoing profiler and a fixed current/temperature measuring array on the Hatteras abyssal plain. A great variety of structures were seen. Immediately above the bottom a well-mixed bottom layer extends vertically 5-60 m, with less than 1 m°C potential temperature change. This mixed layer is often capped by a region of strong vertical potential temperature gradient, with up to 100-m°C potential temperature change in -10 m. The boundary layer may be uniform for 10 km or exhibit a bottom temperature gradient of up to 20 m°C/ km. Interior layers of nearly constant potential temperature and horizontal extent of 2-100 km are seen -25% of the time above the bottom mixed layer. When an interior layer is present, the bottom mixed layer is thinner. On many occasions an interior layer was seen to be horizontally continuous with the bottom mixed layer, suggesting formation of interior layers by detachment of the bottom mixed layer. A benthic front was observed. Differential horizontal advection is required to explain the observed structures. Velocity fluctuations above I cph increase in energy near the bottom, presumably a signature of turbulence in the mixed layer;these fluctuations are modulated by the passage of structures observed in the moored record.
  • Technical Report
    SOFAR float Mediterranean outflow experiment data from the first year, 1984-1985
    (Woods Hole Oceanographic Institution, 1986-07) Price, James F. ; McKee, Theresa K. ; Valdes, James R. ; Richardson, Philip L. ; Armi, Laurence
    In October, 1984, the Woods Hole Oceanographic Institution SOFAR float group began a three-year long field program to observe the low frequency currents in the Canary Basin. The principal scientific goal was to learn how advection and diffusion by these currents determine the shape and amplitude of the Mediterranean salt tongue. Fourteen floats were launched at a depth of 1100 min a cluster centered on 32N, 24W, and seven other floats were launched incoherently along a north/south line from 24N to 37N. At the same time investigators from Scripps Institution of Oceanography and the University of Rhode Island used four other SOFAR floats to tag a submesoscale lens of Mediterranean water. Slightly over twenty years of float trajectories were p reduced during the first year of the experiment. In this report we briefly describe the 1984 field operations and show the first year's SOFAR float data. Perhaps the most striking result is that westward flow within the Mediterranean salt tongue was found to be confined to a rather narrow jet {roughly 150 km in meridional extent) which had a mean speed of roughly 2 em s -l. To the north or south of this jet the mean flow was much weaker and eastward. This suggests that currents associated with the salt tongue itself {rather than the gyre scale circulation) may be most important for determining the salt distribution.
  • Technical Report
    Effects of variations in eddy diffusivity on property distributions in the oceans
    (Woods Hole Oceanographic Institution, 1979-12) Armi, Laurence
    The hypothesis that variations in eddy diffusivity may be responsible for some of the observed distributions of oceanic scalars is explored. A gradient in eddy diffusivity affects property distributions much as would an additional velocity field from regions of high to low eddy diffusivity. In support of such an interpretation, the cross-isopycnal distribution of density is compared with an eddy diffusivity prescribed by the combination of boundary mixing and isopycnal exchange. Since the surface area available for boundary mixing varies with depth, similar variations are reflected in property distributions. For isopycnal distributions, an eddy diffusivity field inferred from the eddy potential energy field description of Dantzler (1977) is compared with the salinity distribution from the Mediterranean Outflow.