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Effects of large-scale motions on turbulent heat and moisture transport in the convective boundary layer

Active Dates 8/15/2021-8/14/2024
Program Area Atmospheric System Research
Project Description
Effects of large-scale motions on turbulent heat and moisture transport in the convective boundary layer

S. Salesky, University of Oklahoma (Principal Investigator)

For over 70 years, Monin-Obukhov similarity theory (MOST) has served as a framework for turbulence closure in the lower atmosphere, allowing one to predict turbulent transport of momentum, heat, moisture, and chemical species between Earth’s surface and the atmosphere, given information about the mean vertical gradient of the quantity of interest and thermal stratification. However, one notable limitation of MOST is that it does not account for the presence of so-called large-scale motions, organized turbulent structures in the lower atmosphere that span a kilometer or more, and that have been shown to play an important role for turbulent exchange processes. Despite recent, compelling insights which have focused primarily on momentum transport, the implications of these large-scale motions for heat and moisture transport are poorly understood. Heat and moisture transport can be significantly different from momentum transport due to atmospheric stability and the structure of the entrainment zone at the top of the daytime convective boundary layer.

The goal of this project is to reveal the physical processes by which large-scale turbulent structures contribute to variability in heat and moisture transport within the convective boundary layer, which are critical for understanding and accurately representing low-level clouds and the hydrological cycle in numerical weather and climate forecasting models. Using observational data collected by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in Northern Oklahoma, and a suite of high-resolution large eddy simulations, we will address the following research questions:
How do large-scale motions impact the large-scale organization of temperature and water vapor?
To what extent is the modulating influence of large-scale motions on heat and moisture transport similar to their influence on momentum transport?
How can the effect of large-scale motions on relationships between turbulent fluxes of heat and moisture and their mean vertical gradients be captured in a generalized similarity framework?
What similarities are there between uniform temperature and humidity zones to uniform momentum zones? How does this spatial organization affect turbulent exchanges of heat and moisture?

This project will lead to improved understanding of the mechanisms by which large-scale motions impact heat and moisture transport in the convective boundary layer, enabling the development of new highly-accurate models to represent boundary layer processes in cloud-resolving, regional, and global forecasting models.
Award Recipient(s)
  • University of Oklahoma Norman (PI: Salesky, Scott)