Interaction of barotropic vortices over topography based on similarity laws: rotating tank experiment and shallow-water simulation

• Published in: Arabian journal of geosciences Vol. 15; no. 3
• Main Author: Chen, Hung-Cheng
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.02.2022; Springer Nature B.V
• Subjects: Barotropic mode; Channeling; Cyclones; Deflection; Earth and Environmental Science; Earth science; Earth Sciences; Flow characteristics; Fluid dynamics; Fluid flow; Hurricanes; Laboratories; Landing; Mountains; Original Paper; Photography; Physical simulation; Physiographic features; Rotation; Shallow water; Similarity; Streak photography; Terrain; Topography; Tropical climate; Tropical cyclones; Typhoons; Vortices; Rotating tank experiment; Shallow-water model; Track deflection of a tropical cyclone; Vortex-topography interaction
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-022-09534-0

When a tropical cyclone encounters terrain features such as the central mountain range (CMR) of Taiwan, the change of motion and structure is complicated and uneasy to predict. Many studies have proposed and attempted to explain the mechanism of the change of motion speed, track deflection, track continuity/discontinuity, and vortex structure. The track deflection mechanism of tropical cyclones before and after landfall has been one of the key topics in operational forecasting in the past decades. In this study, we simplify the real tropical cyclone interacting with terrain problem into the interaction between a barotropic vortex and isolated topographic feature, which is the subject of the rotating tank experiment. According to the dynamic and geometric similarity conditions, the suitable parameters of laboratory experiments are determined. A monopolar vortex is generated stably in a rotating tank by the stirring method. A scaled 3D elliptical hill places on the sloping bottom of the rotating tank. The results show an S-shape track deflection and structural changes of the vortex passing through the elliptic hill by streak photography. A modified shallow-water model (MSWM) proposes to verify the experimental results in the rotating tank. The results showed that the orographic blocking effect slowed down the laboratory vortex as it approached the terrain before landing. When the landing position of the vortex is closer to the north of the terrain, the channeling effect is more significant. When the vortex lands towards the middle of the terrain, the vortex remains axisymmetric after landing due to the insignificant channeling effect. Compared with experimental observation, the calculated results of MSWM show a good agreement in terms of the structure change of vortex and track deflection. This study also carefully examines the relative importance of several β-like effects of historical typhoons and laboratory vortices to identify their track behaviors and flow features. It is worth noting that the ratio of topographic β effect to planetary β effect determines the degree of track deflection of vortex when passing through the terrain. The results show that under dynamic and geometric similarity conditions, the trajectory and flow characteristics of historical typhoons and laboratory vortices through the terrain may show a certain degree of similarity.