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Moore, AM, Arango HG, Di Lorenzo E, Miller AJ, Cornuelle BD.  2009.  An Adjoint Sensitivity Analysis of the Southern California Current Circulation and Ecosystem. Journal of Physical Oceanography. 39:702-720.   10.1175/2008jpo3740.1   AbstractWebsite

Adjoint methods of sensitivity analysis were applied to the California Current using the Regional Ocean Modeling Systems (ROMS) with medium resolution, aimed at diagnosing the circulation sensitivity to variations in surface forcing. The sensitivities of coastal variations in SST, eddy kinetic energy, and baroclinic instability of complex time-evolving flows were quantified. Each aspect of the circulation exhibits significant interannual and seasonal variations in sensitivity controlled by mesoscale circulation features. Central California SST is equally sensitive to wind stress and surface heat flux, but less so to wind stress curl, displaying the greatest sensitivity when upwelling-favorable winds are relaxing and the least sensitivity during the peak of upwelling. SST sensitivity is typically 2-4 times larger during summer than during spring, although larger variations occur during some years. The sensitivity of central coast eddy kinetic energy to surface forcing is constant on average throughout the year. Perturbations in the wind that align with mesoscale eddies to enhance the strength of the circulation by local Ekman pumping yield the greatest sensitivities. The sensitivity of the potential for baroclinic instability is greatest when nearshore horizontal temperature gradients are largest, and it is associated with variations in wind stress concentrated along the core of the California Current. The sensitivity varies by a factor of similar to 1.5 throughout the year. A new and important aspect of this work is identification of the complex flow dependence and seasonal dependence of the sensitivity of the ROMS California Current System (CCS) circulation to variations in surface forcing that was hitherto not previously appreciated.

Hoteit, I, Cornuelle B, Thierry V, Stammer D.  2008.  Impact of resolution and optimized ECCO forcing on Simulations of the tropical pacific. Journal of Atmospheric and Oceanic Technology. 25:131-147.   10.1175/2007jtecho528.1   AbstractWebsite

The sensitivity of the dynamics of a tropical Pacific Massachusetts Institute of Technology (MIT) general circulation model (MITgcm) to the surface forcing fields and to the horizontal resolution is analyzed. During runs covering the period 1992-2002, two different sets of surface forcing boundary conditions are used, obtained 1) from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis project and 2) from the Estimating the Circulation and Climate of the Ocean (ECCO) assimilation consortium. The "ECCO forcing" is the "NCEP forcing" adjusted by a state estimation procedure using the MITgcm with a 1 degrees x 1 degrees global grid and the adjoint method assimilating a multivariate global ocean dataset. The skill of the model is evaluated against ocean observations available in situ and from satellites. The model domain is limited to the tropical Pacific, with open boundaries located along 26 degrees S, 26 degrees N, and in the Indonesian throughflow. To account for large-scale changes of the ocean circulation, the model is nested in the global time-varying ocean state provided by the ECCO consortium on a 1 grid. Increasing the spatial resolution to 1/3 degrees and using the ECCO forcing fields significantly improves many aspects of the circulation but produces overly strong currents in the western model domain. Increasing the resolution to 1/6 degrees does not yield further improvements of model results. Using the ECCO heat and freshwater fluxes in place of NCEP products leads to improved time-mean model skill (i.e., reduced biases) over most of the model domain, underlining the important role of adjusted heat and freshwater fluxes for improving model representations of the tropical Pacific. Combinations of ECCO and NCEP wind forcing fields can improve certain aspects of the model solutions, but neither ECCO nor NCEP winds show clear overall superiority.

Roemmich, D, Gilson J, Cornuelle B, Weller R.  2001.  Mean and time-varying meridional transport of heat at the tropical subtropical boundary of the North Pacific Ocean. Journal of Geophysical Research-Oceans. 106:8957-8970.   10.1029/1999jc000150   AbstractWebsite

Ocean heat transport near the tropical/subtropical boundary of the North Pacific during 1993-1999 is described, including its mean and time variability. Twenty-eight trans-Pacific high-resolution expendable bathythermograph (XBT)/expendable conductivity-temperature-depth (XCTD) transects are used together with directly measured and operational wind estimates to calculate the geostrophic and Ekman transports. The mean heat transport across the XBT transect was 0.83 +/- 0.12 pW during the 7 year period. The large number of transects enables a stable estimate of the mean field to be made, with error bars based on the known variability. The North Pacific heat engine is a shallow meridional overturning circulation that includes warm Ekman and western boundary current components flowing northward, balanced by a southward flow of cool thermocline waters (including Subtropical Mode Waters). A near-balance of geostrophic and Ekman transports holds in an interannual sense as well as for the time mean. Interannual variability in geostrophic transport is strikingly similar to the pattern of central North Pacific sea level pressure variability (the North Pacific Index). The interannual range in heat transport was more than 0.4 pW during 1993-1999, with maximum northward values about 1 pW in early 1994 and early 1997. The ocean heat transport time series is similar to that of European Centre for Medium-Range Weather Forecasts air-sea heat flux integrated over the Pacific north of the XBT line. The repeating nature of the XBT/XCTD transects, with direct wind measurements, allows a substantial improvement over previous heat transport estimates based on one-time transects. A global system is envisioned for observing the time-varying ocean heat transport and its role in the Earth's heat budget and climate system.