Simulations of the Motion of Tropical Cyclone-like Vortices in the Presence of Synoptic and Mesoscale Circulations

Initial mesoscale vortex effects on the tropical cyclone (TC) motion in a system where three components coexist (i.e., an environmental vortex (EV), a TC, and mesoscale vortices) were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically. Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases. However, they may have a more significant impact on the TC track under the following circumstances. First, the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region. This configuration may last for 8 h, and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion. Second, two mesoscale vortices located in the EV circulation may merge, and the merged vortex shifts into the EV inner region, intensifying both the EV and steering flow for the TC, increasing speed of the TC.