• 대기
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• 제23권1호
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• pp.1-11
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• 2013

The angular momentum transport of an idealized axisymmetric vortex in the developing stage was investigated using the Weather Research and Forecast (WRF) model. The balanced axisymmetric vortex was constructed based on an empirical function for tangential wind, and the temperature, geopotential, and surface pressure were obtained from the balanced equation. The numerical simulation was carried out for 6 days on the f-plane with the Sea Surface Temperature (SST) set as constant. The weak vortex at initial time was intensified with time, and reached the strength of tropical cyclone in a couple of days. The Absolute Angular Momentum (AAM) was transported along with the secondary circulation of the vortex. Total AAM integrated over a cylinder of radius of 2000 km decreased with simulation time, but total kinetic energy increased rapidly. From the budget analysis, it was found that the surface friction is mainly responsible for the decrease of total AAM. Also, contribution of the surface friction to the AAM loss was about 90% while that of horizontal advection was as small as 8%. The trajectory of neutral numerical tracers following the secondary circulation was presented for the Lagrangian viewpoint of the transports of absolute angular momentum. From the analysis using the trajectory of tracers it was found that the air parcel was under the influence of the surface friction continuously until it leaves the boundary layer near the core. Then the air parcel with reduced amount of angular momentum compared to its original amount was transported from boundary layer to upper level of the vortex and contributed to form the anti-cyclone. These results suggest that the tropical cyclone loses angular momentum as it develops, which is due to the dissipation of angular momentum by the surface friction.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.329-332
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• 2002

A theoretical study is made of the steady flow of a compressible fluid in a rapidly rotating finite cylinder. Flow is generated by imposing mechanical and/or thermal disturbances at the rotating endwall disks. Both the Ekman and Rossby numbers are small. A detailed consideration is given to the energy budget for a control volume in the Ekman boundary layer. A combination of physical variables, which is termed the energy contents, consisting of temperature and modified angular momentum, emerges to be relevant. The distinguishing features of a compressible fluid, in contrast to those of an incompressible fluid, are noted. For the Taylor-Proudman column to be sustained, in the interior, it is shown that the net energy transport between the solid disk wall and the interior fluid should vanish. Physical rationalizations are facilitated by resorting to the concept of the afore-stated energy content.