Publications

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2013
Giglio, D, Roemmich D, Cornuelle B.  2013.  Understanding the annual cycle in global steric height. Geophysical Research Letters. 40:4349-4354.   10.1002/grl.50774   AbstractWebsite

Steric variability in the ocean includes diabatic changes in the surface layer due to air-sea buoyancy fluxes and adiabatic changes due to advection, which are dominant in the subsurface ocean. Here the annual signal in subsurface steric height (eta' below 200 db) is computed on a global scale using temperature and salinity profiles from Argo floats. The zonal average of over a season (e.g., eta'(March) - eta'(December)) is compared to the wind-forced vertical advection contribution (Delta eta'(w)) both in the global ocean and in different basins. The results show agreement that extends beyond the tropics. The estimate of Delta eta'(w) is based on the Ekman pumping and assumes that the seasonal vertical velocity is constant over the depth range of interest. This assumption is consistent with annual isopycnal displacements inferred from Argo profiles. The contribution of horizontal advection to Delta eta' is significant in some regions and consistent with differences between Delta eta' and Delta eta'(w).

Subramanian, AC, Miller AJ, Cornuelle BD, Di Lorenzo E, Weller RA, Straneo F.  2013.  A data assimilative perspective of oceanic mesoscale eddy evolution during VOCALS-REx. Atmospheric Chemistry and Physics. 13:3329-3344.   10.5194/acp-13-3329-2013   AbstractWebsite

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.