A novel gravity wave transport parametrization for global chemistry climate models: description and validation

Abstract

The gravity wave drag parametrization of the Whole Atmosphere Community Climate Model (WACCM) has been modified to include the wave-driven atmospheric vertical mixing caused by propagating, non-breaking, gravity waves. The strength of this atmospheric mixing is represented in the model via the ‘effective wave diffusivity’ coefficient (Kwave). Using Kwave, a new total dynamical diffusivity (KDyn) is defined. KDyn represents the vertical mixing of the atmosphere by both breaking (dissipating) and vertically propagating (non-dissipating) gravity waves. Here we show that, when the new diffusivity is used, the downward fluxes of Fe and Na between 80 and 100 km largely increase. Larger meteoric ablation injection rates of these metals (within a factor 2 of measurements) can now be used in WACCM, which produce Na and Fe layers in good agreement with lidar observations. Mesospheric CO2 is also significantly impacted by the additional source of vertical mixing, with the largest CO2 concentration increase occurring between 80-90 km, where model-observation agreement improves. However, in regions where the model overestimates CO2 concentration, the new parametrization exacerbates the model bias. The summer mesopause in both hemispheres cools significantly, by up to 35 K, and shifts upward, partially correcting the WACCM low summer mesopause. Our results highlight the far-reaching implications and the necessity of representing vertically propagating, non-breaking, gravity waves in climate models. This method way of modelling gravity waves contributes to growing evidence that it is time to move away from dissipative-only gravity wave parametrizations.

Impact of Atmospheric Compressibility and Stokes Drift on the Vertical Transport of Heat and Constituents by Gravity Waves

“…The transport parameters, K H , K Wave , and ξ inst , can be computed from these profiles. The results show that it is important to include unresolved wave transport by nonbreaking waves in atmospheric models, especially in the upper atmosphere where wave‐driven diffusion can reduce thermosphere densities by enhancing the downward transport of O into the mesopause region (e.g., Gardner, 2018; Pilinski & Crowley, 2015; Qian et al., 2009), alter mesopause region temperatures by, among other effects, transporting CO 2 upward thereby enhancing radiative cooling, and speed the transport of cosmic dust ablation products into the lower atmosphere (Guarino, et al., 2024). Observations of temperatures, winds, and turbulence, made throughout the atmosphere, in combination with the expressions derived here, can now be used to assess the significance of wave transport at all altitudes and to model its effects.…”

“…This latter approach was used by Guarino et al. (2024) to compute ξ inst from data provided by the wave parameterization scheme in the WACCM (see Appendix , Guarino et al., 2024).…”

“…To derive the correct temperature fluctuation variances from the parameterized waves in the WACCM scheme, it was necessary for Guarino et al. (2024) to incorporate diffusive damping by waves and turbulence. Their approach can also be applied to other models, which don't currently include diffusive damping, by using the K zz that is computed when waves dissipate or break, and the wave diffusivities derived here from theory.…”

“…Most recently, Guarino et al. (2024) implemented the K Wave /K H parameterization proposed by Gardner et al. (2019) in the Whole Atmosphere Community Climate Model (WACCM, e.g.…”