Abstract
Abstract. The steering principle of tropical cyclone motion has been applied to tropical cyclone forecasting and research for nearly 100 years. Two fundamental questions remain unanswered. One is why the steering flow plays a dominant role in tropical cyclone motion, and the other is when tropical cyclone motion deviates considerably from the steering. A high-resolution numerical experiment was conducted with the tropical cyclone in a typical large-scale monsoon trough over the western North Pacific. The simulated tropical cyclone experiences two eyewall replacement processes. Based on the potential vorticity tendency (PVT) diagnostics, this study demonstrates that the conventional steering, which is calculated over a certain radius from the tropical cyclone center in the horizontal and a deep pressure layer in the vertical, plays a dominant role in tropical cyclone motion since the contributions from other processes are largely cancelled out due to the coherent structure of tropical cyclone circulation. Resulting from the asymmetric dynamics of the tropical cyclone inner core, the trochoidal motion around the mean tropical cyclone track cannot be accounted for by the conventional steering. The instantaneous tropical cyclone motion can considerably deviate from the conventional steering that approximately accounts for the combined effect of the contribution of the advection of the symmetric potential vorticity component by the asymmetric flow and the contribution from the advection of the wave-number-one potential vorticity component by the symmetric flow.
Highlights
The environmental steering principle has been applied to tropical cyclone track forecasting for nearly 100 years (Fujiwara and Sekiguchi, 1919; Bowie, 1922), which states that a tropical cyclone tends to follow the large-scale flow in which it is embedded
Based on the potential vorticity tendency (PVT) diagnostics, this study demonstrates that the conventional steering, which is calculated over a certain radius from the tropical cyclone center in the horizontal and a deep pressure layer in the vertical, plays a dominant role in tropical cyclone motion since the contributions from other processes are largely cancelled out due to the coherent structure of tropical cyclone circulation
We find that the contribution of the horizontal advection (HA) term is significantly correlated with those of the vertical advection (VA) and diabatic heating (DH) terms, suggesting the relationship between the vertical motion and the relative flow
Summary
The environmental steering principle has been applied to tropical cyclone track forecasting for nearly 100 years (Fujiwara and Sekiguchi, 1919; Bowie, 1922), which states that a tropical cyclone tends to follow the large-scale flow in which it is embedded. As a rule of thumb, the conventional steering flow has been extensively used in tropical cyclone track forecasting and understanding of tropical cyclone motion (e.g., Simpson, 1948; Riehl and Burgner, 1950; Chan and Gray, 1982; Fiorino and Elsberry, 1989; Neumann, 1993; Wu and Emanuel, 1995a, b; Wang and Holland, 1996b, c; Wu et al, 2011a, b). Under the PVT paradigm, in this study we use the output from a high-resolution numerical experiment to address the aforementioned two fundamental issues that are important to understanding tropical cyclone motion. The present study focuses on the numerical experiment without the influences of land surface and topography
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