资源环境科技发展态势分析平台

In July-August (JA) 2018, the western Pacific subtropical high (WPSH) was stronger than normal. Its ridge line was located the most north in history and the position was above three times of the standard deviation. On the intra-seasonal timescale, the high ridge was mostly more north than normal from July 5 till the end of August in 2018 and had two significant northward jumps in the first 10 days and last 5 days of July 2018, respectively. The convective activities in the western Pacific should play an important role in the extremely north WPSH in JA 2018. The convection over the western Pacific was the strongest in JA 2018 during the past 38 years. It induced significant subsidence anomalies, an anomalous low-level anticyclone and positive anomalies of 500-hPa geopotential height in eastern East Asia. On the daily timescale, the northward movement of the active convection over the western Pacific occurred about 5 days earlier than the northward jump of the WPSH. Additionally, the strong and long-lasting Madden-Julian oscillation in the western Pacific (Phase 6) also favoured the suppressed convection and positive anomalies of 500-hPa geopotential height in eastern East Asia. This result could provide a good precursor signal about 5 days advance for the northward jump of the WPSH in summer.