Mechanism of Turbulence Structure Evolution in the Nocturnal Boundary Layer during the Interaction of Low-Level Jet and Internal Gravity Waves: Based on Full Boundary Layer Turbulence Observations

In a stable boundary layer (SBL), turbulence is generally weak and exhibits significant intermittent characteristics. Interactions among motions of different scales complicate its structural evolution, making it difficult to predict. This study focuses on two typical processes in the SBL: Low-Level Jet (LLJ) and Internal Gravity Waves (IGWs), investigating how their interactions influence the evolution of turbulence structures. Utilizing a full boundary layer turbulence observation and data processing system at Zhongchuan International Airport, this study includes eddy covariance system, Doppler Lidar, and wind profiling radar. In a strongly SBL, turbulence energy accumulates in higher layers and, during downward transfer, generates local LLJ and IGWs, triggering intermittent turbulence events. The internal factors of turbulence intermittency dominated the process. The interaction between LLJ and IGWs maintains intermittent turbulence burst, accompanied by the conversion of sub-mesoscale energy to turbulent energy. In a weakly SBL, the conversion of sub-mesoscale motion energy drives intermittent turbulence events, along with energy transfers between different scales of IGWs, resulting in weaker turbulence intermittency. The external factors of turbulence intermittency dominated the process. In both cases, the interaction between LLJ and IGWs alters turbulence structure and atmospheric stability. Turbulent mixing changes the mean gradient field, further influencing the LLJ height. This study elucidates the mechanisms of interaction between internal and external factors in turbulence intermittency. It outlines energy transfer among different scales of motion and clarifies the mechanisms behind state transitions and structural evolution of strongly and weakly SBL. These findings are significant for advancing theoretical research and simulation developments of the SBL.