2023年4月23日和5月6日阿克苏地区东部出现极端低温霜冻天气（简称“4.23”过程和“5.6”过程），尤其“5.6”过程库车市出现历史最晚终霜。基于常规观测、L波段探空、NCEP/NCAR 1°×1°逐6 h再分析等资料，利用天气动力学方法对比分析2次极端低温过程环流背景，高低空配置、冷空气及冷平流强度、锋生作用等，探讨极端低温霜冻成因。结果表明：（1） 两者有共性也有差异，共性表现在2次过程500 hPa阿克苏地区东部均受低槽（低涡）后部西北气流携带冷空气影响，且温度梯度大，锋区增强；均有深厚冷平流自阿克苏西部沿高层偏北气流向阿克苏地区东部低层下传；低温时段贴地层均有逆温和明显锋生，锋生与冷空气进入南疆盆地的路径及低温持续时间对应，且高层能量锋区较强，中低层锋区在增强过程中有斜压不稳定发展；均在霜冻出现前6 h冷平流强度增至最大，冷平流与8 ℃以上降温区域对应较好，且850 hPa温度降至3~4 ℃，对低温霜冻预报有一定指示性。（2） 不同点在于“4.23”过程冷空气为西北路径，西翻和东灌冷空气共同影响阿克苏地区，贴地层逆温明显偏强，为辐射+平流降温；“5.6”过程冷空气为偏北路径，较强冷高压翻越天山进入南疆盆地，同时有东灌冷空气补充，影响范围大、逆温弱但整层降温明显，以辐射降温为主。（3） “5.6”过程低涡在新疆维持时间长，其冷空气及锋区强度、假相当位温梯度及影响时间均较“4.23”过程更强，灾害更重。

Extreme low-temperature frosts occurred in eastern Aksu Prefecture, Xinjiang, China on April 23 and May 6, 2023 (“4.23” process and “5.6” process for short, respectively). Particularly, the latest frost in history appeared in Kuqa City during the “5.6” process. In this study, based on conventional observation data, L-band sounding data, and 6-h reanalysis data of NCEP/NCAR 1°×1°, we contrastively analyze the circulation background, circulation configurations of high and low altitudes, cold air intensity, cold advection intensity, and frontogenesis during two extreme low-temperature processes using weather dynamics. Moreover, the causes of extreme low-temperature frosts are discussed. We realized both common characteristics and differences between the two processes. (1) The common characteristics are as follows: The temperature of eastern Aksu at 500 hPa is affected by northwest flow with cold air at the back of the low trough (low vortex), with a great temperature gradient and strong frontal zone during the two processes. Deep cold advection flows from the upper level of western Aksu to the lower level of eastern Aksu along the northern flow. Temperature inversion and obvious frontogenesis occur in the near-surface layer during the low-temperature period. Frontogenesis corresponds to the path of cold air entering the southern Xinjiang basin and the low-temperature duration. In addition, the upper-level energy frontal zone is stronger, and the mid-low-level energy frontal zone gradually strengthens with baroclinic instability. The cold advection intensity increases to a maximum of 6 h before frost. The cold advection can significantly decrease the temperature of the Aksu area from above 8 ℃ to 3-4 ℃ at 850 hPa, indicating strong frost. (2) The differences are as follows: The cold air invades the Aksu Prefecture from the northwest path in the “4.23” process. The air temperature in the Aksu Prefecture is affected by both “Xifan (flowing over the mountains from west)” and “Dongguan (injecting from east)” cold air. The temperature inversion in the near-surface layer is enhanced by radiation and advection cooling. However, the cold air passes over Tianshan Mountains with a strongly cold high pressure and then invades the southern Xinjiang basin from the northern path in the “5.6” process, accompanied by “Dongguan” cold air. The influence range is large, and the temperature inversion is weak. However, the temperature of the entire layer is significantly reduced, mainly via radiation cooling. (3) The low vortex of the “5.6” process lasts for a long time in Xinjiang. The cold air and frontal zone intensity, potential pseudo-equivalent temperature gradient, and influence time are stronger than those of the “4.23” process, resulting in a more severe disaster.