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NOAA Ship Ronald H. Brown Completes Tw0-Month Study in Eastern Pacific

Ronald H. Brown was part of the Variability of the American Monsoon Systems' (VAMOS) Ocean-Cloud-Atmosphere-Land Study (VOCALS) in the Eastern Pacific off the coasts of Chile and Peru in October and November of 2008.  VOCALS is a NOAA, NSF, and NASA-sponsored investigation of the physical mechanisms that keep the ocean in a large region west of the coast so cold. Ronald H. Brown joined five aircraft from the U.S. and Britain and a Peruvian research vessel in a 2-month regional study of oceanography, meteorology, and biology in the region, which is covered by low stratocumulus clouds.  Multiple observing instruments aboard the ship

Stratocumulus clouds and ocean eddies play a major role in cooling the ocean but, strange as it may sound, oceanic biology may also play a key role.  In a complex chain of processes, plankton emit a biogenic gas that gets into the air and eventually forms aerosol particles that are condensation sites for cloud droplets. This increases the shading efficiency of the clouds and cools the ocean.  Ocean eddies not only transfer cold water out from the coast, but also may enhance the nutrients to stimulate plankton growth.

For this study, Ronald H. Brown fielded one of the most comprehensive sets of observing systems ever assembled on a research vessel.  The ship was festooned with 6 seatainer laboratories and all manner of instruments including five meteorological radars, a Doppler Lidar, four different ocean profiling systems, and a variety of chemical, aerosol, and biological measurements. Some 40 scientists have participated in two deployment legs.  The science party included representatives from three NOAA labs, 13 universities, and three research laboratories in Chile and Peru. 

The ship’s missions included annual servicing of two climate buoys west of Chile on the 20 S latitude line, Getting ready to deploy a buoyinvestigating the dynamics of eddies shed from the coastal upwelling zone, and finding links between the clouds, aerosols, biogenic gas, and biological activity.

As part of the effort to investigate stratocumulus cloud formation over the large region off the coast of Peru and Chile, scientists from Woods Hole Oceanographic Institution, IMARPE (Peru), and U. Chile are collaborating to investigate oceanic eddies (or vortices) in this region. We believe that these eddies, which form near the coast in a region where winds bring cold, deep waters to the surface, may play a role in carrying the cold waters offshore. This contributes to lowering the surface ocean temperatures and, therefore, cloud formation.  These eddies are quite large, about 100km in diameter, and their surface expression is partly visible from satellite images. From the ship, we then measure water properties with depth, as well as collect water samples, to understand their deeper structure, their nutrient content, and their role as microcosms of higher ocean productivity.  The figure below shows a satellite rendering of these eddies with the Brown’s cruise track.  Satellite image of eddies with ship's track

One of the factors that controls the amount of sunlight reflected back to space is the brightness of clouds. In marine areas, this is controlled to some degree by a gas that is created by algae. The University of Hawaii group is studying the emission of this dimethyl sulfide gas to the atmosphere, so that its impact can be more accurately described in numerical climate models.  The University of Washington, NOAA Pacific Marine Environmental Laboratory, and SIO groups are studying the aerosols; Bigelow Laboratory (Maine) is studying the plankton and their sensitivity to solar radiation. NOAA Earth System Research Laboratory's Physical Sciences Division and Chemical Sciences Division and the University of Miami are using remote sensors to study the atmospheric boundary layer and its interaction with the clouds.

Lowering an instrument into the water to measure velocity, temperature and salinityThe aerosol studies involve measuring the number and size and chemical composition of particles in the air above the ocean.  The chemical analysis can tell us about the origin of the particles; that is, whether they come from the ocean surface, the upper atmosphere, or are brought to the area with winds from coastal regions and pollution sources.  These particles have a strong effect on clouds and determine in part where they form, how long they last, and whether they produce rain or not. 




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