Research on the “No-Typhoon July” in 2020 and Typhoon Frequency Variations in July in Recent 70 Years

By using China National Climate Center’s 74 circulation characteristics, DERF2.0, BCC-CSM models and Wenzhou Typhoon Network data, and using linear regression, correlation coefficients and other research methods, the variations about typhoon frequency in July from 1951 to 2020 and the large-scale circulation system in July 2020 are analyzed. The results show that 1) in the recent 70 years, the frequency of typhoon generation has slowly decreased, while the frequency of landing typhoons in China has slowly increased; 2) typhoon frequency has varying degrees of negative correlation with the intensity of subtropical high in different regions of the northern hemisphere, especially with the area index and intensity index of the South China Sea subtropical high; 3) in July 2020, the area and intensity of the subtropical high in the Northwest Pacific were abnormally large and strong. Easterly winds prevailed in the tropics, and the cross-equatorial airflow was weak, resulting in a severe reduction in the frequency of typhoon generation, leading to “no-typhoon” events.