Precursor dynamical factors in the local lower atmosphere of warm-sector heavy rainfall over South China: evidence from wind profiler radar observations

Abstract

Abstract. Using 14 wind profiler radars and hourly records at 3000 weather stations during 2016–2020, 226 warm-sector heavy rainfall (WSHR) events were identified in Guangdong, South China. Five indices reflecting the vertical structure of the atmosphere were analyzed as precursor dynamical signals of WSHR occurrence – the Low-Level Jet Index (LLJI), Vertical Wind Shear (VWS), Atmospheric Lifting Intensity (ALI), and Boundary Layer Height (BLH). Notable fluctuations in signals were found 1–4 h before precipitation onset, and the sensitivity and occurrence mechanisms of WSHR in the three regions showed marked regional differences. In western Guangdong, LLJI increased sharply 1–2 h before onset and, although not linearly correlated with rainfall intensity, was systematically higher in strong-rainfall events. LLJI was also significantly correlated with upper-level (3–5 km) ascent, indicating that the strengthening of the low-level jet can directly enhance upward motion and thereby increase precipitation intensity. In central Guangdong, VWS at 0.5–1.5 km was significantly positively correlated with precipitation intensity across three consecutive pre-onset periods, which may reflect frictional deceleration of the low-level jet and the resulting enhancement of low-level convergence. In eastern Guangdong, anomalously weak upper-level ascent and higher convective available potential energy appeared before strong-rainfall events, indicating that suppressed mid-to-upper-level ascent allowed unstable energy to accumulate. Strong events were significantly warmer at 925 hPa, but showed no significant differences in large-scale vertical velocity or low-level relative humidity, suggesting that the instability accumulation was driven mainly by boundary layer warming; the anomalously high BLH is a manifestation of this thermal instability build-up.