Numerical impacts on tracer transport: Diagnosing the influence of dynamical core formulation and resolution on stratospheric transport
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atsc-JAS-D-21-0085.1.pdf
Description
Published version
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1.88 MB
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Adobe PDF
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53efa43dad641208245fb4b71c619395
Author(s)
Gupta, Aman
Gerber, Edwin P
Plumb, R Alan
Lauritzen, Peter H
Date Issued
September 15, 2021
Journal
Journal of the Atmospheric Sciences
Publisher
American Meteorological Society
Citation
Gupta, A., E. P. Gerber, R. A. Plumb, and P. H. Lauritzen, 2021: Numerical Impacts on Tracer Transport: Diagnosing the Influence of Dynamical Core Formulation and Resolution on Stratospheric Transport. J. Atmos. Sci., 78, 3575–3592.
Version
Final published version
Abstract
Accurate representation of stratospheric trace gas transport is important for ozone modeling and climate projection. Intermodel spread can arise from differences in the representation of transport by the diabatic (overturning) circulation versus comparatively faster adiabatic mixing by breaking waves, or through numerical errors, primarily diffusion. This study investigates the impact of these processes on transport using an idealized tracer, the age of air. Transport is assessed in two state-of-the-art dynamical cores based on fundamentally different numerical formulations: finite-volume and spectral element. Integrating the models in free-running and nudged tropical wind configurations reveals the crucial impact of tropical dynamics on stratospheric transport. Using age-budget theory, vertical and horizontal gradients of age allow comparison of the roles of the diabatic circulation, adiabatic mixing, and the numerical diffusive flux. Their respective contribution is quantified by connecting the full 3D model to the tropical leaky pipe framework of Neu and Plumb. Transport by the two cores varies significantly in the free-running integrations, with the age in the middle stratosphere differing by about 2 years primarily due to differences in adiabatic mixing. When winds in the tropics are constrained, the difference in age drops to about 0.5 years; in this configuration, more than half the difference is due to the representation of the diabatic circulation. Numerical diffusion is very sensitive to the resolution of the core, but does not play a significant role in differences between the cores when they are run at comparable resolution. It is concluded that fundamental differences rooted in dynamical core formulation can account for a substantial fraction of transport bias between climate models.
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DOI of Published Version
https://doi.org/10.1175/JAS-D-21-0085.1
