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Characterizing Boundary Layer Processes During Transition Periods With Observations and Modeling

Active Dates 9/1/2023-8/31/2026
Program Area Atmospheric System Research
Project Description
Characterizing Boundary Layer Processes During Transition Periods with Observations and Modeling

Timothy J. Wagner, University of Wisconsin–Madison, Principal Investigator
David D. Turner, NOAA Global Systems Laboratory, Co-Principal Investigator
Thijs Heus, Cleveland State University, Co-Investigator
Siwei He, NOAA Global Systems Laboratory / CIRES, Co-Investigator

The planetary boundary layer (PBL) is the layer of the atmosphere closest to the Earth’s surface, and surrounds virtually all human activity Many important processes occur within the PBL, including the two-way transfer of energy between the surface and the air. In general, the PBL experiences two steady states: a daytime convective boundary layer with significant turbulence and mixing, and a shallow stable boundary layer at night characterized by little vertical motion. The transitions that occur with sunrise and sunset are more complex since processes that could be safely ignored during the steady-state periods have much greater impacts during the transition periods. Parameters like entrainment (the engulfing of air from above the PBL), subsidence (large scale sinking of air from aloft), and advection (wind bringing in air with different amounts of heat and moisture) are critical for understanding the evolution of PBL structure, but until recently have been difficult to measure. This has made it a challenge to numerically model the PBL during transition times.

This research team has recently developed techniques to measure several of these challenging processes, enabling us to fully quantify the heat and moisture budgets of the PBL and monitor how they evolve throughout the day, including during the transition periods. We have previously evaluated these techniques during the daytime boundary layer, and now we are using them to investigate the transition periods where the relative influence of these previously under-observed forcings is much greater.

We are conducting model and observation studies of two different locations: the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) facility in Oklahoma, a region dominated by wheat and other cropland, and the new ARM Third Mobile Facility (AMF3) Southeast U.S. deployment in the Bankhead National Forest (BNF) in Alabama. These significantly different land covers will cause very different heat and moisture fluxes from the surface into the PBL, resulting in different influences on the evolution of the PBL. By using the observations from these sites and comparing them to large eddy simulation (LES), single column, and mesoscale models, we will investigate how the atmosphere evolves during the transition, the roles of understudied processes like advection, and the relative impact of the different surface types.  We will pay special attention to the solar eclipses that were experienced by the SGP site in 2017 and will be experienced by both sites in 2024, as a solar eclipse causes the same transitions as sunrise and sunset except on a much faster time scale. With the results from these investigations, we expect to improve understanding of important PBL processes as well as improve model representation of the PBL and land-atmosphere interactions.
Award Recipient(s)
  • NOAA/OAR (PI: Turner, David)
  • University of Wisconsin, Madison (PI: Wagner, Timothy)