Revisiting the steering principal of tropical cyclone motion in a numerical experiment

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.

Tornado-scale vortices in the tropical cyclone boundary layer: numerical simulation with the WRF–LES framework

“…In this study a semi-idealized numerical simulation is conducted using version 3.2.1 of the WRF model. Following Wu and Chen (2016), two steps were taken to construct the initial conditions for the numerical experiment. A symmetric vortex was first spun up without the environmental flow on an f plane for 18 h and then the vortex was embedded in the large-scale background of Typhoon Matsa (2005) from 00:00 UTC 5 August to 12:00 UTC 6 August.…”

“…The model is run for 36 h and the 1/9 km resolution and 1/27 km resolution domains are activated at 24 h. In the following analysis, we will focus on the hourly output from 26 to 36 h. The TC center is determined with a variational approach in which it is located until the maximum azimuthal mean tangential wind speed is obtained (Wu et al, 2006).…”

Tornado-Scale Vortices in the Tropical Cyclone Boundary Layer: Numerical Simulation with WRF-LES Framework

“…In this study the numerical simulation is conducted using version 3.2.1 of the WRF model. Following Wu and Chen (2016), two steps were taken to construct the initial conditions for the numerical experiment. A symmetric vortex was first spun up without the environmental flow on an f-plane for 18 hours and then the vortex was embedded in the large-scale background of Typhoon Matsa (2005) from 0000 UTC 5 August to 1200 UTC 6 August.…”

Recent Progress in the Fundamental Understanding of Tropical Cyclone Motion

“…Recently, Wu and Chen (2016) conducted the potential vorticity tendency (PVT) diagnosis for the sub-kilometer high-resolution simulation of Typhoon Matsa (2005) to address the question why the steering flow is important in TC motion. They found that the conventional deep-layer-mean steering, which is optimally determined over a certain radius from the TC center (defined as the geometric center of the circle on which the azimuthal-mean tangential wind reaches a maximum), plays a dominant role in TC motion because the contributions from other processes are largely canceled out due to the coherent structure of the TC circulation.…”