Publication Date:
2022-10-26
Description:
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(3), (2019): 2088-2109, doi:10.1029/2018JC014583.
Description:
As observations and models improve their resolution of oceanic motions at ever finer horizontal scales, interest has grown in characterizing the transition from the geostrophically balanced flows that dominate at large‐scale to submesoscale turbulence and waves that dominate at small scales. In this study we examine the mesoscale‐to‐submesoscale (100 to 10 km) transition in an eastern boundary current, the southern California Current System (CCS), using repeated acoustic Doppler current profiler transects, sea surface height from high‐resolution nadir altimetry and output from a (1/48)° global model simulation. In the CCS, the submesoscale is as energetic as in western boundary current regions, but the mesoscale is much weaker, and as a result the transition lacks the change in kinetic energy (KE) spectral slope observed for western boundary currents. Helmholtz and vortex‐wave decompositions of the KE spectra are used to identify balanced and unbalanced contributions. At horizontal scales greater than 70 km, we find that observed KE is dominated by balanced geostrophic motions. At scales from 40 to 10 km, unbalanced contributions such as inertia‐gravity waves contribute as much as balanced motions. The model KE transition occurs at longer scales, around 125 km. The altimeter spectra are consistent with acoustic Doppler current profiler/model spectra at scales longer than 70/125 km, respectively. Observed seasonality is weak. Taken together, our results suggest that geostrophic velocities can be diagnosed from sea surface height on scales larger than about 70 km in the southern CCS.
Description:
This research was funded by NASA (NNX13AE44G, NNX13AE85G, NNX16AH67G, NNX16AO5OH, and NNX17AH53G). We thank Sung Yong Kim for providing the high‐frequency radar spectral estimates and the two anonymous reviewers for providing useful comments and suggestions that greatly improved the manuscript. High‐frequency ALES data for Jason‐1 and Jason‐2 altimeters are available upon request (https://openadb.dgfi.tum.de/en/contact/ALES). Both AltiKa and Sentinel‐3 altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS; http://www.marine.copernicus.eu). D. M. worked on the modeling component of this study at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). High‐end computing resources were provided by the NASA Advanced Supercomputing (NAS) Division of the Ames Research Center. The LLC output can be obtained from the ECCO project (ftp://ecco.jpl.nasa.gov/ECCO2/LLC4320/). The ADCP data are available at the Joint Archive for Shipboard ADCP data (JASADCP; http://ilikai.soest.hawaii.edu/sadcp).
Description:
2019-08-21
Keywords:
Mesoscale
;
Submesoscale
;
Internal gravity waves
Repository Name:
Woods Hole Open Access Server
Type:
Article
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