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Abstract
Temperature and salinity data obtained from the northwestern Weddell Sea during March 1986 reveal numerous thermohaline staircases in the thermocline separating warm deep water from the overlying colder, lower salinity winter water. Staircases in the upper, steeper portion of the thermocline were characterized by layers having vertical extents of 1–5 m. Layer thicknesses in the deeper, weaker portion of the thermocline were far greater, sometimes exceeding 100 m. The former staircases are referred to as Type A, and the latter as Type B. Vertical gradients in temperature and salinity decreased abruptly across the boundary between Type A and Type B staircase regions. Mean density ratios Rρ were 1.52 and 1.36 over the depth intervals containing Type A and Type B staircases, respectively. Type A staircases were present at all sites sampled, whereas Type B staircases were present over approximately the central 50% of the area sampled.
Laboratory-derived results show that the observed time and vertical space scales for the Type B staircases are consistent with the notion that they are maintained by double diffusive processes. These results, combined with temperature-salinity analyses, lead us to suggest that the Type B staircase regime may have originated as a vertically convective feature within which staircases have formed and evolved continually through double diffusion. Laboratory-derived flux laws are used to estimate upward buoyancy flux due to heat flux through the Type B staircase regime of order 2 × 10−1 m2 s−1, consistent with values derived previously using oceanographic, atmospheric and sea ice data and an order of magnitude greater than computed double diffusive heat fluxes through the Type A staircase regime. The broad areas coverage of Type B staircases, coupled with previous observation of these features at scattered sites throughout much of the Weddell Sea, suggests that they are widespread there and may play a significant role in regional vertical heal transfer.
Abstract
Temperature and salinity data obtained from the northwestern Weddell Sea during March 1986 reveal numerous thermohaline staircases in the thermocline separating warm deep water from the overlying colder, lower salinity winter water. Staircases in the upper, steeper portion of the thermocline were characterized by layers having vertical extents of 1–5 m. Layer thicknesses in the deeper, weaker portion of the thermocline were far greater, sometimes exceeding 100 m. The former staircases are referred to as Type A, and the latter as Type B. Vertical gradients in temperature and salinity decreased abruptly across the boundary between Type A and Type B staircase regions. Mean density ratios Rρ were 1.52 and 1.36 over the depth intervals containing Type A and Type B staircases, respectively. Type A staircases were present at all sites sampled, whereas Type B staircases were present over approximately the central 50% of the area sampled.
Laboratory-derived results show that the observed time and vertical space scales for the Type B staircases are consistent with the notion that they are maintained by double diffusive processes. These results, combined with temperature-salinity analyses, lead us to suggest that the Type B staircase regime may have originated as a vertically convective feature within which staircases have formed and evolved continually through double diffusion. Laboratory-derived flux laws are used to estimate upward buoyancy flux due to heat flux through the Type B staircase regime of order 2 × 10−1 m2 s−1, consistent with values derived previously using oceanographic, atmospheric and sea ice data and an order of magnitude greater than computed double diffusive heat fluxes through the Type A staircase regime. The broad areas coverage of Type B staircases, coupled with previous observation of these features at scattered sites throughout much of the Weddell Sea, suggests that they are widespread there and may play a significant role in regional vertical heal transfer.
Abstract
Vertical fluxes of momentum and sensible heat have been measured above the sea surface by the direct dissipation method. Measurements were made over the open ocean from the Scripps Floating Instrument Platform (FLIP) during the Barbados Oceanographic and Meteorological Experiment (BOMEX). The results are compared with simultaneous measurements of the fluxes by the profile, dissipation, and eddy correlation methods.
The momentum flux was inferred from the rate of viscous dissipation ε above the sea surface. The dissipation was determined by integrating the velocity derivative spectra after correcting the spectra for filter response. The friction velocity (u *) corrected for diabatic effects was 17.4 cm sec−1, corresponding to a shear stress τ=0.35 dyn cm−2. Profile measurements by the University of Washington gave the same value of u * in agreement with the present results. Measurements of momentum flux by Oregon State University (OSU) and the University of British Columbia using dissipation and eddy correlation methods gave somewhat higher values. Correction of the Kolmogoroff inertial subrange constant used in the OSU dissipation calculations gives fluxes in good agreement with the present work.
The sensible heat flux was inferred from the rate of dissipation χ of temperature variance. The temperature derivative spectra were corrected for instrument response and integrated to obtain values of χ. The average value of the sensible heat flux was 0.74 mW cm−2, in reasonable agreement with the profile and eddy correlation measurements. A value of sensible beat flux of 2.8 mW cm−2 has been reported by OSU using the dissipation technique. Correction of the temperature inertial subrange constant used by OSU lowered their heat flux to 1.1 mW cm−2.
Abstract
Vertical fluxes of momentum and sensible heat have been measured above the sea surface by the direct dissipation method. Measurements were made over the open ocean from the Scripps Floating Instrument Platform (FLIP) during the Barbados Oceanographic and Meteorological Experiment (BOMEX). The results are compared with simultaneous measurements of the fluxes by the profile, dissipation, and eddy correlation methods.
The momentum flux was inferred from the rate of viscous dissipation ε above the sea surface. The dissipation was determined by integrating the velocity derivative spectra after correcting the spectra for filter response. The friction velocity (u *) corrected for diabatic effects was 17.4 cm sec−1, corresponding to a shear stress τ=0.35 dyn cm−2. Profile measurements by the University of Washington gave the same value of u * in agreement with the present results. Measurements of momentum flux by Oregon State University (OSU) and the University of British Columbia using dissipation and eddy correlation methods gave somewhat higher values. Correction of the Kolmogoroff inertial subrange constant used in the OSU dissipation calculations gives fluxes in good agreement with the present work.
The sensible heat flux was inferred from the rate of dissipation χ of temperature variance. The temperature derivative spectra were corrected for instrument response and integrated to obtain values of χ. The average value of the sensible heat flux was 0.74 mW cm−2, in reasonable agreement with the profile and eddy correlation measurements. A value of sensible beat flux of 2.8 mW cm−2 has been reported by OSU using the dissipation technique. Correction of the temperature inertial subrange constant used by OSU lowered their heat flux to 1.1 mW cm−2.
