Thermocline bulk shear analysis in the northern North Sea

Chen, Shengli; Polton, Jeff A.; Hu, Jianyu; Xing, Jiuxing. 2016 Thermocline bulk shear analysis in the northern North Sea. Ocean Dynamics, 66 (4). 499-508.

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Thermocline bulk shear is investigated in the northern North Sea using historical observations. The conventional bulk shear is modified to define a thermocline bulk shear (TBS), in order to better represent the shear across the thermocline. The TBS computed by observed currents is decomposed into components at different frequency bands. The near-inertial TBS is the largest component. Its dominance is significant during the period of high wind. It is formed by the wind-driven near-inertial current which has a distinct phase shift (∼180°) across the thermocline. A linear model is presented, which well simulates the observed near-inertial TBS, especially during the period of relatively strong wind. The semidiurnal TBS makes a secondary contribution to the total TBS. It is only slightly smaller than the near-inertial TBS when the wind is relatively weak. The large values of semidiurnal TBS are associated with semidiurnal currents which have a phase shift (∼30–40°) or a magnitude difference (∼5 cm/s) across the thermocline. The low-frequency (<0.7 cpd) TBS also makes an episodic contribution to the total. Its variation coincides with the Ekman transport during the period of relatively strong wind. The low-frequency TBS is mainly formed by an Ekman-like clockwise spiraling of velocity with depth or a distinct magnitude difference in velocities between upper and lower layers.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 1616-7341
Additional Keywords: hermocline bulk shear; Near-inertial; Semidiurnal; North Sea
Date made live: 21 Apr 2016 12:07 +0 (UTC)

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