Mechanism for initial brows-like meso-scale vortex effects on tropical cyclone track

Abstract

We used a two-dimensional quasi-geostrophic barotropic model simulation to study effects of an initial brows-like meso-scale vortex on tropical cyclone (TC) track. Our results show that the impact of each of the three foundational factors (the environmental current, the asymmetric structure and the asymmetric convection system) on TC track varies with time and the importance of each of the factors is different for the different TC motion time period. They show two kinds of the effects. One is a direct way. The asymmetric outer wind structure and the positive longitudinal wind speed averaged in radial-band (100–300) km in the period of (0–11) h are caused by the introduction of the initial brows-like meso-scale vortex, which results in TC track to turn to the north from the northwest directly. The other is an indirect influence. First, initial TC axisymmetric circulation becomes a non-axisymmetric circulation after the addition of the meso-scale vortex. The initial non-axisymmetric circulation experiences an axisymmetrizational process in the period of (0–11) h. Second, axisymmetrizationed TC horizontal size is enlarged after t=12 h. Third, both the TC asymmetric structure and the TC energy dispersion induced-anticyclone are intensified, which quickens the TC motion and results in the track to turn to the north indirectly. The TC motion is characterized by the unusual track under the direct and the indirect effect. The formation of the unusual track should be attributed to the common effects of three factors, including the environmental flow, the TC asymmetric structure and the asymmetric convection system.