资源环境科技发展态势分析平台

During early boreal summer 2020, the western North Pacific (WNP) was characterized by record-low tropical cyclone (TC) activity, reaching the lowest historical level since 1979. Only one short-lived TC was observed in June and the whole of July underwent an unprecedented quiescent TC period. Concurrent Indian Ocean warming provided unfavorable conditions for cyclogenesis over the WNP, which partly (∼40%) explains the extremely low TC number from a statistical standpoint. Accompanied with the Indian Ocean warming, an unprecedentedly long-lasting Madden-Julian Oscillation (MJO) event stalled over the Indian Ocean sector, persisting almost through the entire June and July. This simultaneous quasi-stationary MJO activity further caused unfavorable background conditions for cyclogenesis in the WNP. The Indian Ocean warming combined with the anomalous MJO conditions together largely (>80%) explain the record-low TC number over the WNP during early summer 2020.