Vertical Cells Driven by Vortices - A Possible Mechanism for the Preconditioning of Open-Ocean Deep Convection

• Main Author: Chu, P. C.
• Other Authors: NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF OCEANOGRAPHY
• Format: Text
• Language: English
• Published: 1990
• Subjects: Snow; Ice and Permafrost; *OCEANS; *CIRCULATION; *CYCLONES; VELOCITY; DENSITY; WATER; CELLS; NUMERICAL ANALYSIS; VORTICES; FLOW FIELDS; AZIMUTH; NORMAL DISTRIBUTION; INSTABILITY; STRATIFICATION; BAROMETRIC PRESSURE; SOLUTIONS(GENERAL); VERTICAL ORIENTATION; SYMMETRY; TANGENTS; INDEXES; MEAN; Ice; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA480188; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA480188

The occurrence of open-ocean deep convection requires a background cyclonic circulation and a preconditioning. Both conditions reduce the stratification of the water column within the cyclonic gyre, which will then become eligible for convection if the surface forcing is sufficiently intense. Therefore, for open-ocean deep convection the generation of vertical cells inside the vortex by any mechanism (not necessary by pure thermodynamical processes) is ultimately important. There are two dynamical mechanisms for inducing vertical cells inside a stably stratified vortex: baroclinic and centrifugal instabilities. The combination of the two is called symmetric instability. In order to verify the importance of symmetric instability on the generation of vertical cells inside the vortex, a tangential velocity field with Gaussian distribution in both radial and vertical under stable stratification is taken as a mean flow field. The disturbances produced from this mean flow are assumed to be two dimensional (no azimuthal dependency) and described by a streamfunction in the radial-vertical sections. This streamfunction satisfies second-order partial differential equation. The numerical solutions show the generation of vertical cells inside the vortex. The strength and structure of these cells largely depend on the four parameters: Burger number Bu = (NH/fR)(2), Rossby number Ro = V/fR, barotropic index m, and baroclinic index m. The larger the values of Ro, m, and m(2), or the smaller the value of Bu (weaker stratification for a given size of vortex), the stronger the vertical circulation. The time rate change of density (density redistribution) generated by a vortex and horizontally averaged inside the vortex, indicates the decrease of density in the lower part of the vortex, and the increase of density in the upper part of the vortex.