Investigation of Derechos in China: Spatiotemporal distribution，environmental characteristics，and morphology of Derechos producing convective systems

Based on the 36 Derechos that occurred in China during 18 years from 2002 to 2019, a study on the spatiotemporal distribution and environmental characteristics of Derechos as well as the morphology of Derechos producing convective systems have been conducted using proximity soundings, surface observations, satellite images, single Doppler weather radar data, and weather radar mosaics data. The results are as follows. (1) Derechos mainly occur in the eastern half of China, including North China, East China, South China, and regions to the south of the Yangtze River. The regions of high occurrence frequency show remarkable seasonal variation, which is manifested as the northward movement during the first phase and the southward movement during the second phase from spring to summer. Derechos activity has significant seasonal changes. They mainly occur from March to August with the highest frequency in June and the lowest in August. The convective systems producing the Derechos tend to initiate around noon, while the Derechos themselves tend to occur between mid-afternoon and early midnight. (2) The main characteristics of environmental parameters of Derechos in China are as follows: The 50th percentile of CAPE is 1420 J/kg, the 50th percentile of the 0—6 km vertical shear is 18.0 m/s, the 50th percentile of DCAPE is 1090 J/kg. (3) The weather pattern of Derechos can be divided into the following four types: The subtropical high periphery type, the weak trough type, the high level dry-cold advection forced type and the strong trough type, among which the strong trough type has the highest frequency and the high level dry-cold advection forced type has the lowest frequency. (4) During the period when the maximum wind gust occurs, the most frequent convective storm type is squall line, the second frequent storm type is multi-cell cluster storm and the third frequent storm type is supercell storm.