A data assimilative perspective of oceanic mesoscale eddy evolution during VOCALS-REx

TitleA data assimilative perspective of oceanic mesoscale eddy evolution during VOCALS-REx
Publication TypeJournal Article
Year of Publication2013
AuthorsSubramanian AC, Miller AJ, Cornuelle BD, Di Lorenzo E, Weller RA, Straneo F
JournalAtmospheric Chemistry and Physics
Volume13
Pagination3329-3344
Date Published2013/03
Type of ArticleArticle
ISBN Number1680-7316
Accession NumberWOS:000316961000025
Keywordsboundary-layer; circulation; cloud; eddies; modeling-system; seasonal cycle; stratus; surface; tropical pacific; variability
Abstract

Oceanic observations collected during the VOCALS-REx cruise time period, 1-30 November 2008, are assimilated into a regional ocean model (ROMS) using 4DVAR and then analyzed for their dynamics. Nonlinearities in the system prevent a complete 30-day fit, so two 15-day fits for 1-15 November and 16-30 November are executed using the available observations of hydrographic temperature and salinity, along with satellite fields of SST and sea-level height anomaly. The fits converge and reduce the cost function significantly, and the results indicated that ROMS is able to successfully reproduce both large-scale and smaller-scale features of the flows observed during the VOCALS-REx cruise. Particular attention is focused on an intensively studied eddy at 76 degrees W, 19 degrees S. The ROMS fits capture this eddy as an isolated rotating 3-D vortex with a strong subsurface signature in velocity, temperature and anomalously low salinity. The eddy has an average temperature anomaly of approximately -0.5 degrees C over a depth range from 50-600 m and features a cold anomaly of approximately -1 degrees C near 150 m depth. The eddy moves northwestward and elongates during the second 15-day fit. It exhibits a strong signature in the Okubo-Weiss parameter, which indicates significant non-linearity in its evolution. The heat balance for the period of the cruise from the ocean state estimate reveals that the horizontal advection and the vertical mixing processes are the dominant terms that balance the temperature tendency of the upper layer of the ocean locally in time and space. Areal averages around the eddies, for a 15-day period during the cruise, suggest that vertical mixing processes generally balance the surface heating. Although, this indicates only a small role for lateral advective processes in this region during this period, this quasi-instantaneous heat budget analysis cannot be extended to interpret the seasonal or long-term upper ocean heat budget in this region.

DOI10.5194/acp-13-3329-2013
Short TitleAtmos. Chem. Phys.
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