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伊犁河谷两次短时强降水过程的雷达特征对比分析

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

  • 摘要: 基于新源C波段双偏振雷达资料结合常规观测资料和ERA5再分析资料,对伊犁河谷东段2023年6月12日和8月7日(简称“6·12过程”和“8·7过程”)两次降水过程的环流形势及雷达特征进行对比分析,得到以下主要结论:(1) “6·12过程”为短时强降水,该过程是由中亚短波槽快速东移引起的,槽前西南气流提供充足水汽供应;“8·7过程”为混合型降水,该过程由中亚长波槽缓慢东移造成,其中中尺度辐合切变线是导致短时强降水的直接影响系统,西南气流叠加副高西侧偏南气流共同输送水汽。(2) 影响两次过程的中尺度对流系统不同,中β尺度线状对流带内中γ尺度对流风暴造成“6·12过程”短时强降水,组合反射率因子CR最大值为50 dBz;中γ尺度块状对流风暴造成“8·7过程”短时强降水,CR最大值为45 dBz,均为低质心强风暴,过程中其他降水阶段,出现中γ尺度块状回波单体,强度低于35 dBz。(3) 两次过程的微物理特征也不同,“6·12过程”5 km以上高度层存在冰相粒子,在下落过程中逐渐融化并不断凝结和碰并增长,1.5°仰角偏振量差分反射率因子ZDR为0—2.4 dB,差分传播相移率KDP为0—3.0 °·km−1,相关系数CC接近1。“8·7过程”中高空无冰相粒子,小雨滴在下落过程中不断碰并增长为高浓度的大雨滴,1.5°仰角偏振量ZDR为2.4—4.0 dB,KDP为0.6—1.8 °·km−1,CC接近1,过程中的其他降水阶段,双偏振量数值变化不大,但高值区范围减小,主要以小范围高浓度和粒子相态均一性强的小雨滴为主。两次过程双偏振量高值区均与强降水中心重叠,具有指示意义。

     

    Abstract: 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.

     

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