Contribution of sea-surface wind curl to the maintenance of the SST gradient along the upstream Kuroshio Extension in early summer

The seasonal cycle of the meridional sea-surface temperature (SST) gradient in the upstream Kuroshio Extension (KE) region was examined using satellite observation data and model simulations. In general, the meridional SST gradient is small in summer. However, in early summer (June and July), the SS...

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Bibliographic Details
Published in:Journal of oceanography 2016-10, Vol.72 (5), p.697-705
Main Authors: Sato, Naoki, Nonaka, Masami, Sasai, Yoshikazu, Sasaki, Hideharu, Tanimoto, Youichi, Shirooka, Ryuichi
Format: Article
Language:English
Subjects:
Earth and Environmental Science
Earth Sciences
Freshwater & Marine Ecology
Marine
Ocean currents
Ocean temperature
Ocean-atmosphere interaction
Oceanography
Original Article
Sea surface temperature
Summer
Surface water
Thermocline
Upstream
Upwelling
Wind
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Summary:The seasonal cycle of the meridional sea-surface temperature (SST) gradient in the upstream Kuroshio Extension (KE) region was examined using satellite observation data and model simulations. In general, the meridional SST gradient is small in summer. However, in early summer (June and July), the SST front is sustained or intensified on the northern side of the KE near the coast of eastern Japan. This observed seasonal cycle was successfully simulated in the North Pacific Ocean model for the Earth Simulator (NP-OFES). Analysis of the forecast data revealed that the vertical profiles of temperature and salinity are shifted upward along the KE in early summer. As a result, the permanent thermocline depth is shallowest during summer, causing a relatively small SST tendency. In addition, significant cyclonic vorticity in the lower atmosphere related to the southwesterly sea-surface wind was found to the south of the KE, associated with the Baiu frontal zone (BFZ). It was inferred that the positive vorticity causes Ekman upwelling over the KE region, resulting in suppressed SST warming on the northern side of the KE. These results suggest that the BFZ contributes to maintaining or strengthening the SST front.
ISSN:0916-8370
1573-868X
DOI:10.1007/s10872-016-0363-3