MSI Seminar

Dust and water ice in the Martian atmosphere

Christopher Lee

University of Toronto

The Martian climate system is dominated by three major component cycles. Each involves the cycling of substances between the surface and atmosphere, with all three cycles coupled through microphysical, thermal, and radiative processes. Carbon dioxide, the main atmospheric gas, freezes onto the polar caps each winter resulting in a large surface pressure cycle, significant seasonal modification of the planetary albedo through surface ice deposition, and vapor-pressure buffering of the atmospheric thermal structure in the winter polar atmosphere.

Particulate mineral dust, lifted from the surface by winds, significantly modifies the atmospheric thermal structure and amplifies the already strong asymmetry between the two solstitial seasons that is driven by a large orbital eccentricity. In extreme cases, radiative feedbacks enhance dust lifting and cause global dust storms that completely obscure the planetary surface. The long term effect of such global events can be found in changing global patterns of surface albedo.

The water cycle interacts strongly with both the dust and carbon dioxide cycles, having a surface source and sink in the polar caps, and in the atmosphere nucleating onto suspended dust to form cloud ice particles. Clouds form in the atmosphere during well defined cloud seasons that are ultimately linked to the preferential availability of water during northern summer and the much cooler state of the atmosphere when the planet is nearer aphelion. As a result, water ice clouds play a key role in the radiative heating and circulation during the Martian summers and in modifying the distribution of atmospheric dust.

Within this context, I will discuss efforts to capture the effect of the dust and water ice in the Martian atmosphere using General Circulation Models (GCMs) as a proxy for the real atmosphere. I will describe the processes responsible for dust lifting and water ice sublimation from the surface and their interaction within the atmosphere. Finally, I will show simulations of the Martian atmosphere using the MarsWRF GCM that includes models of these processes, and I will discuss the combined influence of aerosols on the thermal and dynamical evolution of the Martian climate system.