Capotondi, A., V. Combes, M. A. Alexander, E. Di Lorenzo and A. J. Miller, 2009:

Low-frequency variability in the Gulf of Alaska from coarse and eddy-permitting ocean models.

Journal of Geophysical Research-Oceans,114, C01017, doi:10.1029/2008JC004983.

Abstract. An eddy-permitting ocean model of the northeast Pacific is used to examine the ocean adjustment to changing wind forcing in the Gulf of Alaska (GOA) at interannual-to-decadal timescales. It is found that the adjustment of the ocean model in the presence of mesoscale eddies is similar to that obtained with coarse-resolution models. Local Ekman pumping plays a key role in forcing pycnocline depth variability and, to a lesser degree, SSH variability in the center of the Alaska gyre and in some areas of the eastern and northern GOA. Along the western coast of the GOA pycnocline depth anomalies result from the southwestward propagation of disturbances excited further upstream, whose propagation speed is consistent with coastally trapped waves. After the 1976-77 climate regime shift the pycnocline exhibited a more pronounced doming, while the SSH field had a more pronounced depression away from the coastal areas with higher SSHs along the coast. Westward Rossby wave propagation is evident in the SSH field along some latitudes, in agreement with altimetric observations. Westward propagation is less noticeable in the pycnocline depth field. Differences between SSH and pycnocline depth are also found when considering their relationship with the local forcing and leading modes of climate variability in the northeast Pacific. In the central GOA pycnocline depth variations are more clearly related to changes in the local Ekman pumping than SSH. While SSH is marginally correlated with both Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) indices, the pycnocline depth evolution is primarily related to NPGO variability.
The intensity of the mesoscale eddy field increases with increasing circulation strength. The eddy field is generally more energetic after the 1976-77 climate regime 67 shift, when the gyre circulation intensified. In the western basin, where eddies primarily originate from intrinsic instabilities of the flow, variations in eddy kinetic energy (EKE) are statistically significant correlated with the PDO index, indicating that eddy statistics may be inferred, to some degree, from the characteristics of the large-scale flow.

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