MOCHA is a collaborative project, partnered with the UK RAPID Program, to measure the heat and freshwater transports of the North Atlantic Ocean. These transports are called the Thermohaline or Overturning Circulation. Simply put, warm waters move poleward at the surface of the ocean, where they cool and sink, to return equatorward in the deep ocean. See a schematic for the North Atlantic Overturning here.

 To measure the Overturning Circulation a large observation program is necessary. The UK has placed moorings at each of the triangles on the map above. Most of the moorings are placed close to topography, for instance at the continental boundaries, or next to the Mid-Atlantic Ridge. This is because the ocean currents are strongest there. The green dots show where the UK scientists are making shipboard measurements across the Atlantic Ocean at latitude 24 N. The box at the western side of the ocean is enlarged below the main map and shows where Miami scientists have placed the MOCHA array of moored instruments (black triangles, UM) and are making shipboard measurements (green circles, NOAA). Blue and red markers indicate auxiliary measurements from other projects in the region (NOAA XBT lines) and ADCP sections (Explorer of the Seas).




The figure above shows the positions of the Miami moorings (A, B, and C) in vertical cross-section, together with the UK moorings (WB0 - 4). MOCHA is designed to measure the so-called Deep Western Boundary Current (DWBC), a narrow and strong current which carries deep waters from the northern North Atlantic (North Atlantic Deep Water) towards the equator, along the continental slope. An average velocity section of the DWBC is shown in color on the same figure. Mooring B is located in the center of the mean flow. The moorings consists of a combination of current meters (CMs), Microcats (to measure salinity, temperature and pressure), profiling current meters (ADCPs), bottom pressure gauges, and surface telemetry buoys to relay data back to the lab daily. Photos of mooring instrumentation and operations can be viewed here. In addition to the moored array, twice-yearly hydrographic sections of the DWBC are being occupied for the duration of the experiment. Molly Baringer of NOAA/AOML leads this part of the project.  Velocity sections of the DWBC from cruises in May and September, 2005 show how variable the flow can be on short time scales - hence the importance of time series measurements from MOCHA.