The Freezing Precipitation over the Middle-Lower Reaches of the Yangtze River during February-March 2009

Abstract

In this paper, the authors analyze the quasi-stationary fronts, surface conditions, and atmospheric stratification processes associated with a freezing precipitation event over the middle-lower reaches of the Yangtze River, especially in the Dabie mountain during February-March 2009. The long duration of freezing precipitation was primarily caused by stationary and anomalous synoptic weather patterns, such as a blocking high pressure in the northern branch and a trough in the southern branch of the westerlies, which resulted in the encounter cold air from northern China and warm moisture from the south. The east-west-oriented, quasi-stationary front (or shear line) found in central China was mostly responsible for producing the precipitation. The warm layer and near-surface frozen layer were located in the lower troposphere along the front zone. Although the warm layer (> 0°C) existed along the whole front, a surface temperature less than 0°C appeared only over the lower-middle reaches of the Yangtze River, especially in the Dabie mountain. Therefore, the surface temperature was the main influencing factor, as the freezing precipitation only happened over the Dabie mountain.

Key Words:

• freezing precipitation
• quasi-stationary front
• stratification
• warm layer