Comparison of Westward/Eastward Movement Processes for Fronts over the Yunnan-Guizhou Plateau

The Yunnan-Guizhou Quasi-Stationary Front (YGQSF) governs sharp weather contrasts over southwest China in winter. The movement of YGQSF is closely related to synoptic-scale processes on the daily scale, while exhibiting significant diurnal variations. Accurately quantifying frontal movement is vital to relevant studies. For the high frontal activity region, this study proposes a new method for quantifying frontal movement and investigates characteristics of YGQSF with daily eastward (EM) and westward (WM) frontal movement. Results show that all front types exhibit consistent diurnal oscillations: eastward movement (0800 to 1600 BJT) followed by westward movement (after 1600 BJT). For WM fronts, large-scale circulation exhibits cold-air outbreak patterns characterized by easterly winds and cold advection over southwest China. Stronger cold-air advection weakens the eastward movement from 0800 to 1600 BJT and amplifies the frontal post-1600 BJT westward movement. Consequently, the front exhibits net westward propagation on the diurnal scale. For EM fronts, large-scale circulation of EM fronts opposes WM fronts at 850 hPa, consistent with waning cold-air intrusion, suggesting EM fronts occur after the cold-air outbreak. Additionally, EM fronts generally exhibit lower cloud cover, weaker intensity, and are situated farther west. The cloud cover on both sides of EM front is smaller than the WM front, which leads to a stronger radiative heating of the cold air east of the front before 1600 BJT. Furthermore, warm advection is observed at the frontal location, which also favours the eastward movement of EM fronts. Those factors eventually result in net eastward retreat on the daily scale.