Modeling the hydrological cycle in the atmosphere of Mars: Influence of a bimodal size distribution of aerosol nucleation particles

TL;DR

This paper introduces a new hydrological cycle model for Mars' atmosphere that incorporates bimodal aerosol particle size distribution, improving the accuracy of water vapor and ice cloud simulations compared to previous mono-modal models.

Contribution

The novel implementation of a bimodal aerosol size distribution in a Martian atmospheric model enhances the simulation of water and ice cloud properties and their seasonal variations.

Findings

Bimodal distribution improves ice cloud mass and opacity predictions.

Simulated cloud properties align better with observational data.

Small aerosol particle excess has minimal impact on water vapor distribution.

Abstract

We present a new implementation of the hydrological cycle scheme into a general circulation model of the Martian atmosphere. The model includes a semi-Lagrangian transport scheme for water vapor and ice, and accounts for microphysics of phase transitions between them. The hydrological scheme includes processes of saturation, nucleation, particle growth, sublimation and sedimentation under the assumption of a variable size distribution. The scheme has been implemented into the Max Planck Institute Martian general circulation model (MPI--MGCM) and tested assuming mono- and bimodal log-normal distributions of ice condensation nuclei. We present a comparison of the simulated annual variations, horizontal and vertical distributions of water vapor and ice clouds with the available observations from instruments onboard Mars orbiters. The accounting for bi-modality of aerosol particle distribution improves the simulations of the annual hydrological cycle, including predicted ice clouds mass, opacity, number density, particle radii. The increased number density and lower nucleation rates brings the simulated cloud opacities closer to observations. Simulations show a weak effect of the excess of small aerosol particles on the simulated water vapor distributions.