Low-level jets (LLJs) play a crucial role in modulating regional weather, air quality, and wind energy resources. In a topographically diverse country like China, the characteristics and driving mechanisms of LLJs are expected to vary significantly. However, a comprehensive understanding of these regional differences has been limited by the lack of coordinated, high-resolution observations. This study bridges this gap using a year-long observational experiment with Doppler wind lidars (DWLs) at three representative sites: Minfeng (MF) (temperate continental climate), Beijing (BJ) (temperate monsoon climate), and Hefei (HF) (subtropical monsoon climate). Our analysis reveals clear contrasts in LLJ regimes: boundary-layer jets (BLJs) dominate in MF and HF, while synoptic-system-related LLJs (SLLJs) prevail in BJ. LLJ-1 category is dominant at all three sites. A double-nose structure of BLJs is observed at 0.5 km in BJ and SLLJ peaks at 1.4 km in HF. Key properties such as jet core height, diurnal phase, and seasonal prevalence exhibit clear regional dependencies. The most frequent jet core heights are 0.7 km in MF, 0.4 km in HF, and 1.5 km in BJ, with peak seasonal activity occurring in May, July, and October, respectively. Jet core height increases with more stringent jet speed criteria at all sites. The time of the lowest LLJ occurrence frequency shows a longitudinal time lag, occurring at 14:00 local time in HF and BJ, and at 16:00 local time in MF, which aligns with the time of peak mixing layer height (MLH) at the corresponding site. The occurrence of nocturnal LLJs (NLLJs) is positively correlated with a deeper MLH, with occurrence frequencies exceeding daytime values during most of the night. The roles of inertial oscillations (IOs) and synoptic forcing in shaping LLJ characteristics are investigated. The most intense IOs occur near the jet core heights and are synchronized with frontal passage events at each site. Case studies of MF and HF suggest that frontal passages can amplify the IO signal, and the diurnal cycle of inertial motions associated with NLLJs is consistent with Blackadar's evening-transition hypothesis. Under strong synoptic forcing, such as in BJ, the IO signal becomes less pronounced. Analysis of synoptic forcing reveals distinct regional influences: in MF, NLLJs are favored by cold fronts, the Tarim easterly jets, and terrain-induced baroclinicity. In HF, they are influenced by the East Asian monsoon and frontal systems; and in BJ, the Northeast China Cold Vortex (NCCV) is the primary synoptic driver with significant influence from complex terrain. This study provides valuable observational insights into the regional variability of LLJs and their associated boundary-layer processes.
A Comparative Study of Low-Level Jets in Different Climate Regions in China Using Multisite Doppler Wind Lidar Observations
Wang M.;Lolli S.Methodology
;Wang Y.;Wang C.;Su L.;Xia H.
2026
Abstract
Low-level jets (LLJs) play a crucial role in modulating regional weather, air quality, and wind energy resources. In a topographically diverse country like China, the characteristics and driving mechanisms of LLJs are expected to vary significantly. However, a comprehensive understanding of these regional differences has been limited by the lack of coordinated, high-resolution observations. This study bridges this gap using a year-long observational experiment with Doppler wind lidars (DWLs) at three representative sites: Minfeng (MF) (temperate continental climate), Beijing (BJ) (temperate monsoon climate), and Hefei (HF) (subtropical monsoon climate). Our analysis reveals clear contrasts in LLJ regimes: boundary-layer jets (BLJs) dominate in MF and HF, while synoptic-system-related LLJs (SLLJs) prevail in BJ. LLJ-1 category is dominant at all three sites. A double-nose structure of BLJs is observed at 0.5 km in BJ and SLLJ peaks at 1.4 km in HF. Key properties such as jet core height, diurnal phase, and seasonal prevalence exhibit clear regional dependencies. The most frequent jet core heights are 0.7 km in MF, 0.4 km in HF, and 1.5 km in BJ, with peak seasonal activity occurring in May, July, and October, respectively. Jet core height increases with more stringent jet speed criteria at all sites. The time of the lowest LLJ occurrence frequency shows a longitudinal time lag, occurring at 14:00 local time in HF and BJ, and at 16:00 local time in MF, which aligns with the time of peak mixing layer height (MLH) at the corresponding site. The occurrence of nocturnal LLJs (NLLJs) is positively correlated with a deeper MLH, with occurrence frequencies exceeding daytime values during most of the night. The roles of inertial oscillations (IOs) and synoptic forcing in shaping LLJ characteristics are investigated. The most intense IOs occur near the jet core heights and are synchronized with frontal passage events at each site. Case studies of MF and HF suggest that frontal passages can amplify the IO signal, and the diurnal cycle of inertial motions associated with NLLJs is consistent with Blackadar's evening-transition hypothesis. Under strong synoptic forcing, such as in BJ, the IO signal becomes less pronounced. Analysis of synoptic forcing reveals distinct regional influences: in MF, NLLJs are favored by cold fronts, the Tarim easterly jets, and terrain-induced baroclinicity. In HF, they are influenced by the East Asian monsoon and frontal systems; and in BJ, the Northeast China Cold Vortex (NCCV) is the primary synoptic driver with significant influence from complex terrain. This study provides valuable observational insights into the regional variability of LLJs and their associated boundary-layer processes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
