An update on blue snow holes

A simple radiative transfer model, new estimates of the imaginary part of ice's refractive index k, and color matching functions are used to simulate colors, as seen by humans, in holes made in snowpacks. This study was inspired by recent photographs, made under overcast skies, that show a dramatic contrast between the lack‐lustre, near‐gray of holes made in a midlatitude snowpack and the vivid blue of snow holes at the South Pole. While this phenomenon has been studied before, new values of k, which are 1–2 orders of magnitude smaller than the old ones in the violet‐blue region, lead to simulated sRGB color profiles that resemble closely the color photographs. Basically, colors are governed by the dependence of snow grain single‐scattering albedo on snow grain size, spectrally varying k, and the number of times photons are scattered by snow grains. It is demonstrated that profiles of upwelling fluxes within a pure snowpack at wavelengths near 0.75 μm can be used to estimate profiles of effective grain size in the uppermost 20–30 cm.