Characteristics of the Wind Field and Low-Level Jets in the Middle and Lower Troposphere over Chengdu, Southwest China

Low‑level jets (LLJs) play an important role in the transport of heat, water vapor, and pollutants. Based on one year of tropospheric wind profiler radar (RWP) observations, this study systematically analyzes the wind field structure in the middle and lower troposphere over the Chengdu region, as well as the vertical distribution and evolution characteristics of LLJs. The results show that the effective detection height of the wind profiler radar reaches 7.4 km throughout the year, demonstrating good consistency with radiosonde data. Horizontal wind speed accelerates significantly above 3 km, with the highest vertical gradient of wind speed occurring in winter. The prevailing wind direction in the lower layer is mainly influenced by mountain‑valley breezes; with increasing altitude, the westerly belt gradually becomes the dominant wind system. Within the atmospheric boundary layer (below 1 km), the wind field exhibits a distinct diurnal variation: easterly winds dominate in the afternoon, shifting to northerly winds at night. The peak surface wind speed occurs in the afternoon, while the peak upper‑level wind speed occurs at night. The occurrence frequency of LLJs is highest in July, followed by April. The prevailing wind directions of LLJs are north‑northeasterly and northeasterly, and the jet core heights are mainly distributed between 0.7 and 1.9 km. Both the occurrence frequency and intensity of LLJs are higher at night than during the day. These findings deepen our understanding of the boundary layer structure over complex basin terrain.