The transition from turbulent to quiescent boundary layers: Application of new data sets and modeling tools

 

Authors

Larry Berg — Pacific Northwest National Laboratory
Rob K Newsom — Pacific Northwest National Laboratory
David D. Turner — NOAA- Global Systems Laboratory
William I. Gustafson — Pacific Northwest National Laboratory
Heng Xiao — Pacific Northwest National Laboratory
Sheng-Lun Tai — Pacific Northwest National Laboratory
Po-Lun Ma — Pacific Northwest National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory

Category

Boundary layer structure, including land-atmosphere interactions and turbulence

Description

Numerous studies have focused on analysis and simulation of convective and stable boundary-layers. Periods with transitions, however, are often neglected due in part to the lack of appropriate data sets. The deployment of a suite of Doppler lidars at the ARM User Facility’s Southern Great Plains site provides a unique opportunity to study changes in the planetary boundary-layer. The continuous Doppler lidar data allows us to look at details of the flow from the surface to the top of the well-mixed layer. In this work, we focus on the transition from turbulent to quiescent conditions near sunset. A cloud free period is selected from the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) field study. We find that the boundary-layer remains turbulent for approximately 60 minutes after the surface heat flux approaches zero, and the rate of decay of the turbulence is weakly related to the height above ground. We also compare the Doppler lidar data set to simulations of the evening transition using three different modeling systems: a mesoscale configuration of the Weather Research and Forecasting (WRF) model using the Mellor-Yamada-Nakanishi-Niino (MYNN) boundary-layer parameterization, the global Energy Exascale Earth System Model (E3SM), and a LASSO-like configuration using an idealized WRF Large-Eddy Simulation. The mesoscale WRF model, in particular, damps the turbulence much more quickly than is observed such that the turbulence kinetic energy is near zero as the surface sensible heat flux changes from positive to negative.