Interannual Variations of the beta Drift of Tropical Cyclones over the Western North Pacific

Tropical cyclone (TC) movement consists essentially of the large-scale environmental steering and the beta drift, and the latter is also affected by large-scale environmental flows. However, few previous studies have been conducted to examine the interannual variations of the beta drift of TCs in the western North Pacific (WNP) basin and the corresponding relationship with the large-scale environmental flow. Using the observed TC tracks and reanalysis dataset during 1965-2019, it is found that the beta drift plays a more important role in the TC motion than environmental steering at the interannual time scale. The westward (northward) component of the beta drift in the environment with anticyclonic relative vorticity is slower (faster) than that with cyclonic relative vorticity, while an equatorward (poleward) relative vorticity gradient decreases (increases) the westward component of the beta drift, in agreement with previous numerical simulations. It is also found that the southwestward migration of the WNP subtropical high can decrease (increase) the westward (northward) component of the beta drift. This study suggests that environmental influence on the beta drift should be considered when understanding interannual variations of TC movement and tracks, which are important to TC landfall, emergency management, and hazard mitigation. Significance StatementThe beta drift is an important component of TC movement and is affected by large-scale environmental flows. However, few previous studies have been conducted to examine the interannual variations of the beta drift of TCs in the western North Pacific basin and the corresponding relationship with the large-scale environmental flow. This study finds that the beta drift plays a more important role in the TC motion than environmental steering at the interannual time scale, and the interannual variations of the beta drift are also controlled by large-scale environmental flows. It is suggested that environmental influence on the beta drift should be considered when understanding interannual variations of TC movement and tracks, which are important to TC landfall, emergency management, and hazard mitigation.