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2016/11/15 14:00 Associate Prof. Shih-Nan Chen（Institute of Oceanography, NTU）
Seminar
Poster： ╱ Post date：2016-11-08NCU IHOS Seminar Announcement
Speaker：Associate Prof. Shih-Nan Chen
Place：S-325, Science Building 1
Abstract：
Title：Stability of bottom-attached, buoyant coastal currents
Speaker：Associate Prof. Shih-Nan Chen
Institute of Oceanography, NTU
Time：11/15（Tue.）14：00
Place：S-325, Science Building 1
Abstract：
Numerical experiments using a three-dimensional, primitive equation ocean model (ROMS) reveal that a range of idealized, bottom-attached, buoyant coastal currents fed by coastal discharge deviate strongly from the cross-shore geostrophic balance. In the body of propagating coastal currents, a wave-like feature of alternating cross-shore flow develops, with current speed of O(10 cm/s) and an along-shore wave spacing of a few baroclinic deformation radii. Increasing coastal discharge and decreasing density anomaly (i.e. reduced gravity) strengthen the cross-shore flow such that the coastal currents eventually become unstable. The classic Eady model, modified to account for the effects of a bottom slope (e.g. Blumsack and Gierasch (1972), is then used to evaluate whether the development of alternating cross-shore flow is a result of growing baroclinic instability. Preliminary analyses are supportive for this hypothesis: cases with large discharge and small reduced gravity generally lie near regions of large linearly growth rate in the stability diagram. The key parameter of this problem is the ratio of bottom slope to isopycnal slope. Decreasing discharge and increasing density anomaly flatten the isopycnal, meaning that there is less available potential energy (APE) to be extracted by the disturbance and thereby tending to stabilize the coastal currents. Moreover, for the unstable cases, the cross-shore velocity is intensified at two vertical boundaries and shows upstream phase tilt with height, generally in accord with the vertical structure of mutually reinforced Eady waves. Typical time scale for the development of alternating cross-shore flow is around 8 to 15 days, implying that these features are observable in the field. In this presentation, energy transfer between the base flow and wave field will be quantified.
Last modification time：2016-10-31 AM 9:32
