New insights into radiative transfer in sea ice derived from autonomous ice internal measurements

Abstract

Abstract. The radiative transfer of short-wave solar radiation through the sea ice cover of the polar oceans is a crucial aspect of energy partitioning at the atmosphere-ice-ocean interface. A detailed understanding of how sunlight is reflected and transmitted by the sea ice cover is needed for an accurate representation of critical processes in climate and ecosystem models, such as the ice-albedo feedback. Due to the challenges associated with ice internal measurements, most information about radiative transfer in sea ice has been gained by optical measurements above and below the sea ice. To improve our understanding of radiative transfer processes within the ice itself, we developed a new kind of instrument equipped with a number of multispectral light sensors that can be frozen into the ice. A first prototype consisting of a 2.3 m long chain of 48 sideward planar irradiance sensors with a vertical spacing of 0.05 m was deployed at the geographic North Pole in late August 2018, providing autonomous, vertically resolved light measurements within the ice cover during the autumn season. Here we present the first results of this instrument, discuss the advantages and application of the prototype and provide first new insights into the spatiotemporal aspect of radiative transfer within the sea ice itself. In particular, we investigate how measured attenuation coefficients relate to the optical properties of the ice pack, and show that sideward planar irradiance measurements are equivalent to measurements of total scalar irradiance.

Development of a Diffuse Reflectance Probe for In Situ Measurement of Inherent Optical Properties in Sea Ice

“…These ice transformations also increase photosynthetically available radiation, which can result, in given conditions, to higher primary production in and under the ice (Arrigo et al, 2012;Arrigo et al, 2008;Fernández-Méndez et al, 2015). Over the past, the inherent optical properties (IOPs) of sea ice parameterized in climate models have been inverted from apparent optical properties (AOPs) measured above and below sea ice (Briegleb and Light, 2007;Holland et al, 2012;Katlein et al, 2020). However, measuring at top and bottom boundaries can't account for the strong depth dependency of the scattering properties inside sea ice.…”