ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 51 Issue 8 > 2025,51(8):978-992. DOI:10.7519/j.issn.1000-0526.2025.031902 Prev Next
Formation Mechanism and Radar Echo Characteristics of a Severe Storm in Southwest Yunnan in 2023
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Abstract:
Based on C-band weather radar products and multi-source observations, the persistent severe storm weather process and two major rainstorm cells in southwest Yunnan during 13-15 March 2023 are analyzed. The results indicate that this severe storm weather process occurred in the circulation background of the surface cold front’s retreating eastward, the establishment and intensification of the southwesterly jet in the low (upper) air, and the persistent intrusion of the mid-level northwesterly flow, and the storm mainly developed and intensified near the crossing area of the mid- and high-altitude jets. The continuous and stable transport of the low-level warm advection and the mid-level cold advection in southwest Yunnan intensified the unstable stratification of the ambient atmosphere. The convective available potential energy (CAPE) was 826.6-1481.6 J·kg-1, the vertical wind shears from 0 to 3 km, and 0 to 6 km were 14.4-19.9 m·s-1 and 27.6-34.5 m·s-1, respectively. The high unstable stratification and the strong vertical wind shear provided good ambient condition for the formation, development and maintenance of the catastrophic storms. The daytime storm was triggered by the coupling of southerly wind uplift forced by warm advection with weak surface convergence lines. The significant thermal and moisture difference on either side of the Wuliang Mountains enhanced the storm’s development. Comparatively, the nighttime storm initially formed near the mid-to-low-level baroclinic frontogenesis zone, triggered by upslope lifting during its moving eastward and intensified under the influence of the low-level southwesterly jet. Under the influence of diurnal difference and diverse topographic forcing, the radar echo characteristics of the storm cells exhibited distinct features. Storm cell No.1 displayed radar echo morphologies such as an inflow notch, a bounded weak echo region (BWER), and a “V” notch, with radial velocity indicating a mesocyclone structure. During the hailfall period, the average composite reflectivity was 60.5 dBz, the average vertically integrated liquid (VIL) was 36.1 kg·m-2, and the average VIL density (VILD) was 4.0 g·m-3. In contrast, storm cell No.2 had a prominent rear-inflow jet and a forward-flank inflow notch, with more pronounced topographic responses in its echo. After crossing the Lancang River, the strong echo area, VIL, and VILD increased abruptly, with VILD rising from 1.7 g·m-3 to 4.5 g·m-3. The life cycles and surface severe weather manifestations of the storm cells differed significantly. Storm cell No.1 had a lifespan of 6 h, accompanied by continuous hailfall during its influence period, with thunderstorm winds observed before and after its passage. The precipitation phase transitioned to a mix of hail and short-term heavy rainfall exceeding 20 mm·h-1 in the later stage. Storm cell No.2 had a lifespan of 3 h, with hailfall occurring only in the later stage of its development. The other types of convective weather were less intense.
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