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Volume 15, issue 13
Atmos. Chem. Phys., 15, 7269-7286, 2015
https://doi.org/10.5194/acp-15-7269-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 7269-7286, 2015
https://doi.org/10.5194/acp-15-7269-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Jul 2015

Research article | 03 Jul 2015

Impact of planetary boundary layer turbulence on model climate and tracer transport

E. L. McGrath-Spangler1,2, A. Molod2,3, L. E. Ott2, and S. Pawson2 E. L. McGrath-Spangler et al.
  • 1Universities Space Research Association, Columbia, MD, USA
  • 2Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 3Earth System Sciences Interdisciplinary Center, University of Maryland, College Park, MD, USA

Abstract. Planetary boundary layer (PBL) processes are important for weather, climate, and tracer transport and concentration. One measure of the strength of these processes is the PBL depth. However, no single PBL depth definition exists and several studies have found that the estimated depth can vary substantially based on the definition used. In the Goddard Earth Observing System (GEOS-5) atmospheric general circulation model, the PBL depth is particularly important because it is used to calculate the turbulent length scale that is used in the estimation of turbulent mixing. This study analyzes the impact of using three different PBL depth definitions in this calculation. Two definitions are based on the scalar eddy diffusion coefficient and the third is based on the bulk Richardson number. Over land, the bulk Richardson number definition estimates shallower nocturnal PBLs than the other estimates while over water this definition generally produces deeper PBLs. The near-surface wind velocity, temperature, and specific humidity responses to the change in turbulence are spatially and temporally heterogeneous, resulting in changes to tracer transport and concentrations. Near-surface wind speed increases in the bulk Richardson number experiment cause Saharan dust increases on the order of 1 × 10−4 kg m−2 downwind over the Atlantic Ocean. Carbon monoxide (CO) surface concentrations are modified over Africa during boreal summer, producing differences on the order of 20 ppb, due to the model's treatment of emissions from biomass burning. While differences in carbon dioxide (CO2) are small in the time mean, instantaneous differences are on the order of 10 ppm and these are especially prevalent at high latitude during boreal winter. Understanding the sensitivity of trace gas and aerosol concentration estimates to PBL depth is important for studies seeking to calculate surface fluxes based on near-surface concentrations and for studies projecting future concentrations.

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PBL processes are important for weather, climate, and tracer transport and concentration. In the GEOS-5 AGCM, the PBL depth is used in the calculation of turbulent mixing. This study analyzes the impact of using different PBL depth definitions in this calculation. Near surface wind speed differences modify Saharan dust on the order of 1e-4kg m-2. CO surface concentrations are modified by up to 20 ppb over biomass burning regions. Instantaneous CO2 differences are on the order of 10 ppm.
PBL processes are important for weather, climate, and tracer transport and concentration. In the...
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