detailed information about TWIST

bathymetry of the experimetal area

The image above represents what one would see from underwater, if one was offshore of the mooring deployment site, looking northwest back towards the continental slope. The bathymentry depicted and mooring positions are the same as what is shown in the contour map below. The bathymetry is approximately to scale, but the moored profilers and HRP are enlarged so they can be seen. The topographic roughness and even spacing between the ridges are important factors in generating the high levelo of mixing we observed during the cruise. Jack Cook in the graphics department morphed the depth data into this figure for us.

Experimental program:

The study area is on the continental slope of the North Atlantic Ocean, near Norfolk Canyon. The area is centered at 37.25N, 74.66W, and was chosen for the evenly spaced topographic waves that run orthogonal to the slope. The experimental site is characterized by well defined, small horizontal scale (2.5 - 3 km horizontal wavelength) ridges oriented onshore-offshore that are superimposed on the large-scale planar slope. The quantification of turbulence generated by these topographic features should show how the length scales of the bathymetric roughness affect mixing.

Three Moored Velocity Profilers (MVPs) were deployed for the whole time at the site. Deployment of the MVPs in a closely spaced array (~500 meter separation) permits the assessment of the horizontal internal wave scales. High Resolution Profiler (HRP) dives were made to quatify the smallest scale components of vertical mixing. Various time and length scales will be sampled with the HRP to provide detailed measurements of the mixing occuring in the experimental area. and quantify the links between the finescale waves and turbulent mixing. As well, the finescale data acquired by the HRP complements the MVP data and extends the horizontal area sampled. In combination, the HRP and MVP data will allow the characterization of the amplitude and direction of propogation of the finescale internal wave field.

The following chart shows the MVP deployment sites, and the near-field stations. The color codes in the bottom left corner show which instrument system was used at the various stations. TS1 indicates the site of timeseries 1. The red lines highlight the contours along which the L and K stations were arrayed.

During this experiment, 265 HRP and CTD/LADCP profiles were made. A summary of them shows which instrument systems was used and the spatial and temporal spacing of the data we collected. The moored profilers were programmed to profile simultaneously every three hours starting a 000h GMT. The three profilers made a total of 813 profiles over the time they were deployed. The details about the MVP configuration and timing are provided in this table. A discussion of the initial scienitific results will be added to the site soon.

1998 Schedule: (includes cruise)

Where to find the data:

As of June 2000, the data from the HRP, CTD/LADCP, and MVP moorings has all been processed, and the various instrument systems inter-calibrated based on the best ground truth methods available.The data from TWIST is stored on computers accessible to researchers in this program.  For their information, the list here provide information on where to access to each type of data.  A technical report is in prepartation that documents the data processing steps completed in the final data set.

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