Wind Stress Curl and Coastal Upwelling in the Area of Monterey Bay Observed during AOSN-II
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Authors
Wang, Q.
Kalogiros, J.A.
Ramp, S.R.
Paduan, J.D.
Buzorius, G.
Jonsson, H.
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Date of Issue
2011-05
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Abstract
Aircraft measurements obtained during the 2003–04 Autonomous Ocean Sampling Network (AOSN-II)
project were used to study the effect of small-scale variations of near-surface wind stress on coastal upwelling
in the area of Monterey Bay. Using 5-km-long measurement segments at 35 m above the sea surface, wind
stress and its curl were calculated with estimated accuracy of 0.02–0.03 N m22 and 0.1–0.2 N m22 per
100 kilometers, respectively. The spatial distribution of wind speed, wind stress, stress curl, and sea surface
temperature were analyzed for four general wind conditions: northerly or southerly wind along the coastline,
onshore flow, and offshore flow. Wind stress and speed maxima frequently were found to be noncollocated as
bulk parameterizations imply owing to significant stability and nonhomogeneity effects at cold SST pools. The
analyses revealed that complicated processes with different time scales (wind stress field variation, ocean
response and upwelling, sea surface currents, and heating by solar radiation) affect the coastal sea surface
temperature. It was found that the stress-curl-induced coastal upwelling only dominates in events during
which positive curl extended systematically over a significant area (scales larger than 20 km). These events
included cases with a northerly wind, which resulted in an expansion fan downstream from Point An˜ o Nuevo
(wind speed peaks greater than about 8–10 m s21), and cases with an offshore/onshore flow, which are
characterized by weak background upwelling due to Ekman transport. However, in general, observations
show that cold pools of sea surface temperature in the central area of Monterey Bay were advected by ocean
surface currents from strong upwelling regions. Aircraft vertical soundings taken in the bay area showed that
dominant effects of the lee wave sheltering of coastal mountains resulted in weak atmospheric turbulence and
affected the development of the atmospheric boundary layer. This effect causes low wind stress that limits
upwelling, especially at the northern part of Monterey Bay. The sea surface temperature is generally warm in
this part of the bay because of the shallow oceanic surface layer and solar heating of the upper ocean.
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The article of record as published may be located at http://dx.doi.org/10.1175/2010JPO4305.1
Series/Report No
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Meteorology
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This work was supported by the Marine Meteorology and Atmospheric Effects program of the Office of Naval Research (ONR) (Awards N0001405WR20338, N0001406WR20081, and N0001407WR20229). S. R. Ramp’s work was supported by ONR Grant N0001403WR20002 (Aerial Surveys of the Ocean and Atmosphere off Central California).
Format
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Journal of Physical Oceanography, Vol. 41, pp. 857-877, May 2011
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.