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During the last two decades, marine stratocumulus clouds
have been the center-piece of many theoretical modeling studies
and field experiments. This type of cloud is mainly observed at
low levels over the eastern side of the subtropical oceans where
the conditions (cool surface waters and warm, dry air subsiding
aloft) favor the creation of a sharp temperature and moisture inversion
that caps the Marine
Atmospheric Boundary Layer (MABL) and leads to the trapping of
the clouds at its top. Although the role of stratocumulus clouds
in affecting the radiation budget
by cooling the ocean was recognized through early studies, the
growing need of a more accurate representation in the Global Climate
Models (GCMs) has engaged many scientists in the pursuit of a better
understanding of their radiative, microphysical and dynamical properties,
the
thermodynamic structure
of the MABL as well as the climatological variability of the respective
areas.
One of the most prevalent stratocumulus cloud decks in
the world is located over the subtropical SE Pacific, extending
about 1500 km offshore, from the Equator all the way south to
central Chile (25-30 S). In addition to the large latitudinal
extent, the interaction with El Nino-Southern Oscillation (ENSO) and the special
morphology of the western South American continent (e.g. the presence of Andes)
also contribute to the unique character and high importance of the SE Pacific
stratocumulus regime. To learn more about the Stratus
experiment, follow the links to the
WHOI Stratus Project or the Environmental Technology Laboratory (ETL)
Pan American Climate Studies (PACS)
Websites.
Under the scope of the PACS (Pan American Climate Studies) Stratus 2004 field experiment, the NOAA Environmental Technology Laboratory (ETL), the University of Miami Radar Meteorology Group and the Texas A&M University Aerosol Research Group deployed a plethora of instruments onboard the NOAA research vessel Ronald H. Brown (RHB) for making measurements of stratocumulus clouds, MBL thermodynamic structure, surface fluxes and meteorology. The research cruise took place in December 2004 (12/05-12/23), about 2 months after the climatological peak of stratus cloud amount, and with a considerable time lag compared to the previous relevant field experiments of EPIC 2001 (October 9-25, 2001) and PACS Stratus 2003 (November 11-24, 2003). Observations
The map (Fig. 1) illustrates the ship track during the Stratus cruises. Although only the first part of the Stratus 2004 cruise (Fig. 2), departure from Arica, Chile and west heading along the 20 S line until 90 W) spatially overlaps with the routes followed during EPIC 2001 and PACS 2003, there is sufficient overlap in domains for crucial intercomparisons between the three field experiments. The dark point on the map represents the location (20 S 85 W) of the WHOI (Woods Hole Oceanographic Institution) Ocean Reference Station (WORS) Fig. 3, the recovery and replacement of which was the primary objective of the cruise (RHB was stationed at this location for 5 days, 12/11-12/16). The final southeastward route until the endpoint at Valparaiso, Chile is unprecedented for a stratocumulus-oriented field study, enabling us to expand the domain of in-situ measurements of the particular stratocumulus regime further south.
Figure 1. The ship departed departure from Arica, Chile, on December 5, 2004, and returned to port December 23.
Figure 2. The NOAA Research Vessel Ronald H. Brown in port in Arica, Chile, during the 2004 Stratus experiment.
Figure 3. WORS deployment and retrieval on the NOAA Research Vessel Ronald H. Brown during the 2004 Stratus experiment.