NARROW BAROTROPIC CURRENTS IMPINGING ON AN ISOLATED SEAMOUNT

Citation
Xz. Zhang et al., NARROW BAROTROPIC CURRENTS IMPINGING ON AN ISOLATED SEAMOUNT, J GEO RES-O, 99(C11), 1994, pp. 22707-22724
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Oceanografhy
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
ISSN journal
2169-9275 → ACNP
Volume
99
Issue
C11
Year of publication
1994
Pages
22707 - 22724
Database
ISI
SICI code
2169-9275(1994)99:C11<22707:NBCIOA>2.0.ZU;2-G
Abstract
Laboratory and numerical experiments concerned with the interaction of homogeneous narrow currents (jets) and tall, isolated topographic fea tures in the presence of background rotation were conducted. The labor atory jets (in an azimuthal direction) were produced in a rotating cir cular test cell using a circularly symmetric, free surface, source sin k technique. By regulating the Rossby and Ekman numbers of the jets, t he narrow currents so created can be either circularly symmetric (stab le) or meandering (unstable). A theoretical analysis for a point sink at the test cell center is advanced to predict the strength and radial distribution of the azimuthal current in the absence of bottom topogr aphy. Laboratory observations are found to be in good agreement with t he model. The interaction of stable currents with isolated topography was investigated. The system parameters are the Rossby and Ekman numbe rs, the normalized topographic width and height, the width of the curr ent, and the position of the streamwise centerline. A numerical model was developed which employed a vertically averaged vorticity equation driven by Ekman layer forcing along the free surface and dissipated by Ekman pumping along the lower bounding surface. The model is supporte d by laboratory observations. Only stable currents are considered for the numerical calculations. Currents which pass either to the right or left of the obstacle center as well as those which impinge directly a re considered. For all cases, anticyclonic motions are found atop the obstacle. In the numerical experiments the maximum values of cyclonic and anticyclonic vorticity above the topography are found to be monoto nically increasing functions of the Rossby number, with other paramete rs fixed. For cases in which the current is to the right of the topogr aphic feature, closed cyclonic vortices are formed in the left topogra phy lee. The normalized area of these cyclones increases with increasi ng Rossby number, for the range of Ro investigated. For all cases the transport stream function lines in the right topography lee are deflec ted relatively more than the corresponding streamlines in cases for wh ich the upstream flow is uniform and rectilinear (i.e., a broad curren t having no relative upstream vorticity).