Optical properties of sea ice doped with black carbon – an experimental and radiative-transfer modelling comparison

Abstract

Abstract. Radiative-transfer calculations of the light reflectivity and extinction coefficient in laboratory-generated sea ice doped with and without black carbon demonstrate that the radiative-transfer model TUV-snow can be used to predict the light reflectance and extinction coefficient as a function of wavelength. The sea ice is representative of first-year sea ice containing typical amounts of black carbon and other light-absorbing impurities. The experiments give confidence in the application of the model to predict albedo of other sea ice fabrics.Sea ices, ∼ 30 cm thick, were generated in the Royal Holloway Sea Ice Simulator (∼ 2000 L tanks) with scattering cross sections measured between 0.012 and 0.032 m 2 kg −1 for four ices. Sea ices were generated with and without ∼ 5 cm upper layers containing particulate black carbon. Nadir reflectances between 0.60 and 0.78 were measured along with extinction coefficients of 0.1 to 0.03 cm −1 (efolding depths of 10-30 cm) at a wavelength of 500 nm. Values were measured between light wavelengths of 350 and 650 nm. The sea ices generated in the Royal Holloway Sea Ice Simulator were found to be representative of natural sea ices.Particulate black carbon at mass ratios of ∼ 75, ∼ 150 and ∼ 300 ng g −1 in a 5 cm ice layer lowers the albedo to 97, 90 and 79 % of the reflectivity of an undoped "clean" sea ice (at a wavelength of 500 nm).

The Roland von Glasow Air-Sea-Ice Chamber (RvG-ASIC): an experimental facility for studying ocean/sea-ice/atmosphere interactions

“…similar to (Marks et al, 2017). Equation 9 represents a light field decaying exponentially with depth.…”

“…Smaller tanks are cheaper to build and run and have better controlled boundary conditions. The cooling method used to form artificial sea ice ranges from cold plates (Cox and Weeks, 1975;Eide and Martin, 1975;Wettlaufer et al, 1997) through the controlled atmosphere of a coldroom (Tison et al, 2002;Style and Worster, 2009;Naumann et al, 2012;Marks et al, 2017) to the outdoors (Rysgaard et al, 2014;Hare et al, 2013). Coldplates provide the tightest control over the upper boundary condition but preclude the study of many processes at the upper interface because the experimental system has no atmosphere.…”

“…Glass and plastic allow the sea ice to be observed through the tank sides. Lighting may be placed above a sea-ice tank to provide illumination for radiative transfer experiments (Perovich and Grenfell, 1981;Marks et al, 2017). Finally, sea-ice tanks are either cuboid (e.g.…”

“…Rysgaard et al, 2014;Nomura et al, 2006;Wettlaufer et al, 1997), cylindrical (e.g. Cox and Weeks, 1975;Perovich and Grenfell, 1981;Loose et al, 2009;Marks et al, 2017), or quasi two-dimensional Hele-Shaw cells (Eide and Martin, 1975;Middleton et al, 2016). Wave generation is easier in a cuboid tank whereas cylindrical tanks will have simpler edge effects.…”

“…Zhou et al, 2014;Notz and Worster, 2008). Laboratory sea ice has helped develop our understanding of radiative transfer in sea ice (Perovich and Grenfell, 1981;Marks et al, 2017), frost flower formation (Style and Worster, 2009;Perovich and Richter-Menge, 1994), the thermodynamics of grease ice and nilas (Naumann et al, 2012;De La Rosa et al, 2011), and many other fields.…”