Investigation of the Nocturnal Boundary Layer during the Land Atmosphere Feedback Experiment (LAFE) in August 2017

Nocturnal low-level jets (LLJs) are important stable boundary layer (SBL) phenomena which can have wide ranging effects on boundary layer processes. LLJs have been shown to affect moisture transport, air quality, shear and turbulence production, as well as controlling the fluxes between the surface and the SBL. Despite the significant impact of LLJs on the boundary layer, much is unknown on the evolution and spatial/temporal variability of the vertical structure of the winds, temperature, and turbulence variables under LLJ conditions due to the difficulty of observing these quantities. As a result, much remains unknown about these processes during LLJ occurrences.

The Land Atmosphere Feedback Experiment (LAFE) conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site during the month of August 2017 provided a unique opportunity to observe LLJs using the large suite of additional instrumentation that was added to the existing ARM-SGP measurement suite. LAFE was an international collaborative effort that brought together several state of the art remote-sensing and in-situ instruments to study the summer time land atmospheric feedbacks. The additional measurements deployed during LAFE allowed observing the LLJ evolution with a much higher resolution in time (~1 min) and height (~5 m) than normally available. In addition to the measurements of wind speed and temperature, the LAFE observations network provided continuous measurements of turbulent kinetic energy (TKE) and momentum flux. These additional observations along with the routinely available measurements from the ARM extended facilities are being used to study the structure and evolution of the nocturnal LLJs.

In this presentation, measurements from LAFE (at the ARM central facility) and from the ARM extended facilities are analyzed to study the dynamic and thermodynamic processes occurring around the formation and evolution of the LLJs. The impact of LLJs on the temperature, TKE, and momentum-flux profiles as well as possible feedback mechanisms will also be investigated.