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Large-scale structure in wind forcing over the California Current System in summer

Large-scale structure in wind forcing over the California Current System in summer AbstractThe wind that drives oceanic eastern boundary upwelling systems is highly variable. In many locations, the standard deviation of wind velocity on time scales of days to weeks is larger than the mean. In the ~1600-km long California Current System (CCS), the spatial decorrelation scale of the wind fluctuations is ~400-800 km, suggesting wind fluctuations in the north and south ends of the system are not related. Yet, there is also the suggestion in the literature of a larger-scale structure in the fluctuations. Here, empirical orthogonal function (EOF) analysis of buoy and satellite wind velocities confirms the existence of that structure. This analysis covers a larger spatial domain than previous EOF studies in the CCS and, to allow for propagation of the wind fluctuations, includes an approach for calculating Hilbert EOFs from time series with gaps. The large-scale structure in the wind fluctuations is a quasi-dipole pattern spanning the coastline from Washington through California. It accounts for ~60% of the wind velocity variance on time scales of days to weeks. The time-mean wind velocity, showing a continuous zone of intensified wind along the coast, is deceptive. When the northern half of the CCS is in a relaxation state, the southern half often experiences intensified winds, and vice versa. There should be a resulting out-of-phase structure in oceanic upwelling. The out-of-phase wind fluctuations in the north and south parts of the CCS may affect the forcing of oceanic coastal-trapped waves, mesoscale eddy generation at capes, and offshore export of carbon. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monthly Weather Review American Meteorological Society

Large-scale structure in wind forcing over the California Current System in summer

Fewings, Melanie R.
Monthly Weather Review , Volume preprint (2017): 1 – Jul 21, 2017
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References (50)

Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0493
DOI
10.1175/MWR-D-17-0106.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe wind that drives oceanic eastern boundary upwelling systems is highly variable. In many locations, the standard deviation of wind velocity on time scales of days to weeks is larger than the mean. In the ~1600-km long California Current System (CCS), the spatial decorrelation scale of the wind fluctuations is ~400-800 km, suggesting wind fluctuations in the north and south ends of the system are not related. Yet, there is also the suggestion in the literature of a larger-scale structure in the fluctuations. Here, empirical orthogonal function (EOF) analysis of buoy and satellite wind velocities confirms the existence of that structure. This analysis covers a larger spatial domain than previous EOF studies in the CCS and, to allow for propagation of the wind fluctuations, includes an approach for calculating Hilbert EOFs from time series with gaps. The large-scale structure in the wind fluctuations is a quasi-dipole pattern spanning the coastline from Washington through California. It accounts for ~60% of the wind velocity variance on time scales of days to weeks. The time-mean wind velocity, showing a continuous zone of intensified wind along the coast, is deceptive. When the northern half of the CCS is in a relaxation state, the southern half often experiences intensified winds, and vice versa. There should be a resulting out-of-phase structure in oceanic upwelling. The out-of-phase wind fluctuations in the north and south parts of the CCS may affect the forcing of oceanic coastal-trapped waves, mesoscale eddy generation at capes, and offshore export of carbon.

Journal

Monthly Weather Review – American Meteorological Society

Published: Jul 21, 2017

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