A Comparative Analysis of Radar Characteristics of Two Short-Term Heavy Precipitation Events in the Ili River Valley

Based on the Xinyuan C-band dual-polarization radar data, combined with conventional observation data and ERA5 reanalysis data, a comparative analysis was conducted on the circulation patterns and radar characteristics of two precipitation events in the eastern section of the Ili River Valley on June 12 and August 7, 2023 (referred to as the "6·12 event" and the "8·7 event"). The results are as follows. (1) The "6·12 event" was characterized by short-term heavy precipitation (SHP), caused by the rapid eastward movement of Central Asian short-wave trough. The southwesterly flow ahead of the trough provided sufficient water vapor. In contrast, the "8·7 event" involved mixed precipitation, resulting from the slow eastward movement of the Central Asian long-wave trough, with mesoscale convergent shear serving as the direct influence system responsible for the SHP. (2) The mesoscale convective systems (MCS) affecting the two events differed. In the "6·12 event", meso-γ-scale convective storms within a meso-β-scale linear convective zone caused the SHP, with a maximum composite reflectivity (CR) value of 50 dBz. In the “8·7 event”, meso-γ-scale clustered convective storms were responsible, with a maximum CR value of 45 dBz. Both events featured strong storms with low mass centers. Other precipitation phases of the "8·7 event" exhibited meso-γ-scale clustered echo cells with intensities below 35 dBz. (3) The microphysical characteristics of the two events also differed. In the "6·12 event", ice-phase particles were present above 5 km, gradually melting and undergoing continuous condensation, collision, and growth during their descent. At the 1.5° elevation angle, the dual-polarization parameters indicated differential reflectivity (ZDR) of 0–2.4 dB, specific differential phase (KDP) of 0–3.0 °·km⁻¹, and co-polar cross-correlation coefficient (CC) of close to 1. During the SHP phase of the "8·7 event", no ice-phase particles were present in the high-altitude layers. Small raindrops continuously collided and grew into a high concentration of large raindrops during their descent. At the 1.5° elevation angle, the dual-polarization parameters showed ZDR of 2.4–4.0 dB, KDP of 0.6–1.8 °·km⁻¹, and CC of near 1. During the non-SHP phase of the "8·7 event", the values of dual-polarization variables did not change significantly, but the extent of high-value area decreased, indicating a dominance of small droplets with high concentrations and strong homogeneity in the particle phase. For both events, the areas of high dual-polarization parameters overlapped with the centers of heavy precipitation, providing indicative insights.