Cloud Characteristics and Synoptic Background Associated with Severe Convective Storms

Severe convective storms happened during 2005—2011 are analyzed and classified into four types based on cloud characteristics and synoptic background. Type Ⅰ locates within the cold air mass, Type Ⅱ is in the rear of westerly trough or cold vortex cloud systems, Type Ⅲ is in Meiyu front or shear line and Type Ⅳ is in the upper trough system which moves eastward from the Tibetan Plateau.Type Ⅰ usually happens in North China, the Huanghuai or Jianghuai areas. Hail, gale and tornados always arise from them. Before severe convective storms initiation, large scale cloud band of front or shear line always appears at the Jiangnan Area or South China. North of the large scale cloud band is the place where the severe convective storms will initiate, where the upper airflow is eastward or southeastward. Cumulus clusters or short troughs moving along the upper airflow are the key factor of the strong convection initiation.Type Ⅱ usually occurs at the east of China and the north of the Yangtze, and the main disaster is thunderstorm, hail and gale. When the water vapor content is plenty, heavy rainfall can also appear. The place where the severe convective storms will initiate is at the rear of the cloud band corresponding to the weather system. North of the cloud band, the anticyclone dry air intrusion is the main characteristics. Although there are weather systems both at the upper and lower altitude, the storms are still difficult to forecast.Type Ⅲ commonly happens during Meiyu period at the Jianghuai, Jiangnan areas or South China. The main disaster is heavy rainfall. There are some meso-scale convective systems imbedded in Meiyu front or shear line cloud band, maintaining for a long time. On water vapor channel image of satellite, the north border of the cloud band is usually trimly, which commonly go with the upper level jet. The south border of the cloud band is usually composed of feather style cirrus cloud. On cloud-derived wind field, the distance between the upper jet stream north of the cloud band and the upper anticyclone ridge is near.Type Ⅳ commonly happens at the east of Southwest China and the west of South China. The main disasters are torrential floods and mudslides. These severe convective storms usually happen at the northwest of subtropical anticyclone when the monsoon is active. The key factor that make them happen is the short trough moving from the Tibetan Plateau, which corresponds to a cloud band. Dark area or dark band after the cloud band can be seen on water vapor images.