Spectral dynamics and turbulence energy cascade in the Martian planetary boundary layer

Abstract:

Planetary boundary layer (PBL) on Mars presents distinct features in terms of its turbulence that severely affects the exchanges of momentum, heat and tracers in the atmosphere. As the radiative forcing varies diurnally, so does the Martian turbulence, there exists extreme eddy patterns on both daytime (i.e. especially local afternoon) and nighttime (i.e. local early night) related to the most intense radiative heating and cooling rates respectively. To illustrate, the daytime PBL leads to strong rising thermals and vortices enhancing the convective activity in the boundary layer, reaching up to nearly 10 km. Whereas the nighttime PBL suppresses the convection, instead, generates local wind-shear, characterized by the intermittent turbulence and eddy bursts [1]. As a consequence of the strong radiative cooling, it results in an extremely shallow (up to a few meters) and stably-stratified boundary layer during the nighttime.

Within this context, in order to reveal the diurnal characteristics of the Martian turbulence, we investigate its spectral dynamics in the present study. This is realized by the analysis of the turbulence spectra, inferred from diurnal large-eddy simulations (LES) utilizing the MarsWRF model [2]. Our results demonstrate the particular characteristics of turbulence spectra at different time episodes on Mars, comparing with Kolmogorov’s inertial subrange theory. This analysis is then further extended by investigating the potential implications of dust events on the turbulence energy cascade. Furthermore, in addition to the numerical results, we support our findings on the turbulence spectra with the in situ measurements on Mars.

[1] Mahrt, L. (1989). Intermittency of atmospheric turbulence. Journal of the Atmospheric Sciences, 46(1), 79-95.

[2] Richardson, M. I., Toigo, A. D., & Newman, C. E. (2007). PlanetWRF: A general purpose, local to global numerical model for planetary atmospheric and climate dynamics. Journal of Geophysical Research: Planets, 112(E9).