Interannual Variability of Baiu Frontal Activity in May and its Connectivity with June

The Baiu front (BF) is generally formed in May in the western North Pacific. Using objective analysis data from 1979 to 2014 (36 years), this study investigated the interannual variability of Baiu frontal activity (BFA) in May (BFA-M). In May, seasonal enhancement of warm and moist southerlies from the tropics climatologically establishes the BF as a large-scale quasi-stationary front. The strength of the southerlies from the tropics also controls the interannual variability of BFA-M. The anomalous large-scale circulation centered around Taiwan, which can be interpreted as a moist Rossby wave from the equatorial Kelvin-Rossby wave packet in the western tropical Pacific, modifies the strength of the southerlies. The equatorial Kelvin-Rossby wave packet, which is identified as the equatorial intraseasonal oscillation (ISO), propagates eastward from the Indian Ocean to the western Pacific.