A Stochastic Parameterization of Non-Orographic Gravity Waves Induced Mixing for Mars Planetary Climate Model

TL;DR

The paper develops a stochastic, surface-to-exosphere parameterization for non-orographic gravity wave–driven mixing in the Mars PCM, linking GW momentum divergence to eddy diffusion within a refined Non-Superadiabatic Principle framework. A comprehensive, altitude-dependent formula for the eddy diffusivity D_{eddy} integrates saturation, critical layers, and viscosity, and couples to diffusion fluxes and tracer transport through an AR-1 update of winds and tracers. Mars PCM simulations show D_{eddy} values from 10^4 to 10^9 cm^2 s^-1 with a turbopause between ~70 and 140 km, varying seasonally, while temperatures are only mildly affected but upper-atmosphere tracers show substantial changes, in good agreement with MCS and NGIMS observations. The results demonstrate that non-orographic GW–induced turbulence can regulate upper-atmosphere processes and tracer escape on Mars, providing a physically consistent, testable enhancement to Martian climate modeling.

Abstract

This paper presents a formalism of mixing induced by non-orographic gravity waves (GWs) to integrate with the stochastic GWs scheme in the Mars Planetary Climate Model. We derive the formalism of GWs and their mixing under the same assumptions, integrating the two schemes within a unified framework. Specifically, a surface-to-exosphere parameterization of GW-induced turbulence has been derived in terms of the eddy diffusion coefficient. Simulations show that the coefficient is on the order of 1E4 to 1E9 cm2 s-1 and a turbopause is at altitudes of 70 to 140 km, varying with seasons. The triggered mixing has minor effects on model temperatures, yet it substantially impacts upper atmospheric abundances. Simulations are consistent with observations from the Mars Climate Sounder and the Neutral Gas and Ion Mass Spectrometer. Mixing enhances the tracer transports in the middle and upper atmosphere, governing the dynamics of these regions. The scheme reveals how non-orographic GW-induced turbulence can regulate upper atmospheric processes, such as tracer escape.

Figures (6)

• Figure 1: Wave saturation altitudes for three basic forms. a) normal case: $z_b$ at the altitudes where maximum of EP-flux take place; b) $z_b=z_0$, the wave breaks once it is launched; c) $z_b$ at the upper most saturation levels.
• Figure 2: Monthly-averaged zonal averaged $D_{eddy}$ ( cm$^2$ s$^{-1}$, upper panels) and zonal drags (m s$^{-1}$ sol$^{-1}$, lower panels) during clear-sky (Ls 60$^\circ$-90$^\circ$ ) and dusty seasons (240$^\circ$-270$^\circ$), MY32. Note that the $D_{eddy}$ is plotted in $\log_{10}$ and the contour lines of the drags are nonlinear and not shown for values less than 10$^{0}$ cm$^2$ s$^{-1}$.
• Figure 3: Monthly-averaged zonal averaged temperature (K) and diurnal tide (K), Ls 60$^\circ$-90$^\circ$, MY32. The temperature in upper panels: a) MCS observations; b) simulations with GWs, c) without GWs, and d) GWs+mixing. Lower panels e)-h) are corresponding diurnal tides.
• Figure 4: Similar to Figure \ref{['temp03']}, but for Ls 240$^\circ$-270$^\circ$, MY32.
• Figure 5: Monthly-averaged zonal averaged $\chi_q$ with $q$= CO, Ar, H$_2$O(vapor), O, MY32. Upper panels: $\chi_q$ during Ls 60$^\circ$-90$^\circ$. Lower panels: $\chi_q$ during Ls 240$^\circ$-270$^\circ$.