Meridional Overturning Circulation and Heatflux Array (MOCHA)
Goal: "To set in place a system for continuous observation of the meridional heat transport in the subtropical Atlantic, with which to document its variability and its relationship to oberved climate fluctuations, and to assess climate model predictions"
Principal Investigators: Bill Johns, Molly Baringer (NOAA-AOML), and Lisa Beal

Velocity Sections of the Deep Western Boundary Current
To compliment MOCHA, two hydrographic surveys of the DWBC will be completed each year, in spring and fall, for the duration of the experiment. These surveys are lead by Molly Baringer at NOAA/AOML and will provide calibration for the mooring array, as well as better spatial detail. Below are shown preliminary direct velocity measurements from two previous cruises, courtesy of Lisa Beal and Tania Casal.

  
The left panel shows a velocity section across the location of the MOCHA line, collected during a survey aboard the RV Knorr in May 2005. The continental slope off Abaco, the eastward island of the Bahamas, is to the left of the section. At the surface the Antilles Current flows northward at the shelf break, with a strong recirculation of waters back towards the south offshore. At depth the usual signature of the DWBC is masked, probably by incoming Rossby Waves. The right panel shows the same section (extending farther offshore), but collected about one week later. Here the recirculation of the Antilles Current is weakened and the deep velocity structure, showing a core of southward moving water at 2500 m depth, is strengthened, but remains unusually weak compared to the mean flow field of the DWBC. These data illustrate how pronounced the short-term variability of the DWBC is!




This section across the MOCHA line was occupied in September 2005 aboard the NOAA Ship Ron Brown. On this occasion the DWBC appears very strong, with velocities up to 30 cm/s at 2000 m depth. Notice the barotropic nature of the offshore flow field, with several recirculations.