Impact of the Kunming Quasi-Stationary Front on Yunnan in 2024

Based on ground observation data, ERA5 reanalysis data, and new vertical sounding data from the Mile Field Research Station for Yungui Quasi-Stationary Front, China Meteorological Administration, this study analyzed the characteristics of the 2024 Kunming quasi-stationary front. A typical case was analyzed to examine the three-dimensional structural characteristics of the front's advance and retreat, as well as precipitation phase change. The results show that a total of 24 Kunming quasi-stationary front processes affected Yunnan in 2024, lasting for 157 d. Compared with the climatological mean, the processes occurred more frequently with weaker intensity, and mainly appeared in winter, spring, autumn and early summer. Among all types, the intensified westward-advancing type was the most frequent. When affected by the Kunming quasi-stationary front, variations in the wind field occur earlier than those in the humidity and temperature fields. Humidity and temperature show uneven vertical distribution with multi-layer structural characteristics. Before the front intensifies and moves westward, the easterly winds over Mile persist longer, extend to higher altitudes and strengthen. The opposite occurs during the maintenance and eastward retreat stages. 3 to 4 h after frontal passage, frontal inversion occurs at heights of 1 to 3 km above Mile. The inversion intensifies during snowfall or rainfall periods, and a deep layer with temperature below 0℃ near the surface is observed during snowfall. In the absence of a front, the vertical profiles of relative humidity and water vapor density exhibit bimodal structures, with high values near the surface and in the middle and upper levels. 5 to 7 h after frontal passage, the low-level moist layer thickens and humidity increases, while the moist layer in the middle and upper levels thins with decreased humidity. Water vapor is mainly concentrated below 2 km. During non-frontal rainfall, the cloud base height decreases, whereas during frontal rainfall, the cloud base height rises. When fog occurs, the cloud base height is less than 250 m. The integrated liquid water content exceeds 1.2 kg/m² during rainfall periods. It is positively correlated with rainfall amount. Both integrated water vapor and integrated liquid water content reach their maximum values prior to the onset of snowfall.