Quantitative characteristics of the quasi-stationary front anchored over the steep terrain on the Yungui Plateau

Abstract

The Yunnan-Guizhou quasi-stationary front significantly influences winter weather in the Yungui Plateau (YGP), bringing low temperature, sharp cooling, and regional precipitation. This study objectively identifies fronts and quantitatively characterizes them in terms of location, orientation, length, intensity, and movement. Furthermore, the three-dimensional circulation and local weather impact for different types are analyzed. From 1971 to 2020, a total of 5125 frontal days were identified. The frontal frequency exhibits a sector-shaped pattern, with its maximum frequency over the northwestern part of the YGP, and five high-frequency belts distribute from the northeast to west. Five front types (C1 to C5; from east to west) anchor over the steep terrain on the YGP. C1 to C3 fronts are northwest-southeast-oriented, and C4 fronts are north-south-oriented, while C5 is northeast-southwest-oriented. East of the fronts, the near-surface northeasterly wind carrying colder air is blocked by the steep terrain and veers upward over the eastern slope. The southwesterly winds west of the fronts transport warmer air above near-surface colder air, forming an inversion layer. In C1 and C2, weak cold air remains north of 25°N, while strong southwesterly flow extends into the eastern lowlands. This causes fronts positioned more eastwardly, with both low-level inversion and the extensive high-frequency precipitation to the east of the fronts. In C4 and C5, strong cold air intrusion into the YGP causes fronts positioned further west. Inversion and high-frequency precipitation concentrate at higher elevations in the western YGP. Quantifying the refined frontal features is crucial for enhancing the accuracy of local weather forecasting.