第一届未来大气科学论坛

    The tropical cyclones (TCs) often cause intense rain and destructive winds. While these catastrophic weather conditions capture our attention, the less-known impact of TCs remains overlooked. This study reveals that TCs have a notable suppressive effect on monsoonal rainfall in southern China when they traverse the South China Sea. This phenomenon can be attributed to the influence of these mesoscale disturbances on the quasi-stationary, large-scale monsoonal circulation, which alters the moisture pathway. Furthermore, the case-by-case analysis indicates that approximately 76% of TCs correspond to rainfall reduction, whereas the other 24% correspond to rainfall increase. The latter is due to the concurrent occurrence of another independent influencing factor: extratropical cyclonic anomalies that promote enhanced rainfall through favoring lower-tropospheric moisture convergence.
    On the other hand, TCs in the tropical western North Pacific can significantly suppress rainfall over the Maritime Continent and its surrounding seas. This suppression effect of TCs exists across all phases of the Madden–Julian Oscillation (MJO), a dominant factor influencing MC rainfall on an intraseasonal timescale. TCs greatly alleviate rainfall enhancement during the convective phases of the MJO and aggravate rainfall suppression during the suppressive phases. Particularly, TCs reduce the likelihood of extremely high rainfall in convective MJO phases from 9% to 5% and increase the likelihood of extremely low rainfall in suppressive MJO phases from 10% to 16%. The rainfall suppression is attributed to the lower-tropospheric southwesterly anomalies to the south of TCs, which result in moisture divergence over the MC. Additionally, the upper-tropospheric equatorward outflows of TCs also promote subsidence and suppress rainfall.

tropical cyclone; rainfall suppression