The Penetration of Solar Radiation Into Water and Carbon Dioxide Snow, With Reference to Mars

Abstract

The depth to which solar radiation can penetrate through ice is an important factor in understanding surface‐atmosphere interactions for icy planetary surfaces. Mars hosts both water and carbon dioxide ice on the surface and in the subsurface. At high latitudes during autumn and winter carbon dioxide condenses to form the seasonal polar cap. This has been both modeled and observed to, in part, occur as snowfall. As snow accumulates, the thermal properties of the surface are changed, whether the underlying surface was rocky, regolith, or a solid ice sheet. This results in a change (usually increase) in albedo, affecting the proportion of the incident solar energy reflected, or transmitted below the surface of the snow layer. The depth to which light can penetrate through this layer is an important parameter in heat transfer models for the Martian surface and is often quantified using the e‐folding scale. We present the first measurements of the e‐folding scale in pure carbon dioxide snow for the wavelengths 300 to 1100 nm alongside new measurements of water snow.

The Penetration of Solar Radiation Into Granular Carbon Dioxide and Water Ices of Varying Grain Sizes on Mars

“…Water ice was made from deionized water, first boiled and then slowly frozen to minimize air bubbles in the ice. The difference between “snow” (as measured previously in Chinnery et al, 2019) and small granular ice is an important distinction, even though the grain size ranges overlap. Snow samples were made by spraying deionized water droplets into liquid nitrogen, and CO 2 snow was made using an Air Liquide Snowpack maker, connected directly to a liquid CO 2 cylinder, both of which made very fine, near‐spherical droplets that tend to clump together, making grain size determination difficult (other than being sieved to <1.18 mm).…”

“…All these issues were significantly less in the larger ice grain sizes. Due to this, we estimate the data errors on grain sizes <1.18 mm to be ±3 mm, as used for the snow e ‐folding scale measurements by Chinnery et al (2019), but for the larger grains >1.18 mm ±2 mm.…”

“…Top: The average (mean) e ‐folding scale is plotted for each grain size and ice composition. The e ‐folding scale of H 2 O and CO 2 snow is plotted (data from Chinnery et al, 2019), in addition to the results from slab ice experiments, of which the CO 2 slab ice e ‐folding scale was published in Chinnery et al (2018). Vertical error bars show the spread of data ±2 mm for experimental errors, horizontal errors denote the grain size ranges.…”

“…Samples were temporarily stored in a sealed insulated container in the freezer at −86 °C. This material was then treated similarly to snow for the light intensity measurements by Chinnery et al (2019). The sieve sizes used for both the H 2 O and CO 2 granular ice experiments were 0.355, 0.50, 0.60, 0.71, 0.85, 1.00, 1.18, 2.00, 3.35, 4.00, 5.60, and 8.00 mm.…”

“…Previous studies have reported the penetration depth of broad‐spectrum solar irradiation in CO 2 ice in its most massive form (Chinnery et al, 2018) and at its finest, as CO 2 snow (Chinnery et al, 2019), but how do these two measurements relate to each other, and what is the behavior exhibited in between these two end‐members? Is this same behavior also seen for water ice?…”