Impact of Microstructure on Solar Radiation Transfer Within Sea Ice During Summer in the Arctic: A Model Sensitivity Study

Abstract

The recent rapid changes in Arctic sea ice have occurred not only in ice thickness and extent, but also in the microstructure of ice. To understand the role of microstructure on partitioning of incident solar shortwave radiation within the ice and upper ocean, this study investigated the sensitivity of the optical properties of summer sea ice on ice microstructures such as the volume fraction, size, and vertical distribution of gas bubbles, brine pockets, and particulate matter (PM). The results show that gas bubbles are the predominant scatterers within sea ice. Their effects on the scattering coefficient and ice albedo are 5 and 20 times stronger respectively than the effect of brine pockets. Albedo and transmittance of ice decrease with higher concentration and larger size of PM particles. A 4-cm top layer of ice with high PM concentration (50 g/m3) results in a 10% increase in radiation absorption. The role of ice microstructure in the partitioning of radiation transfer is more important for seasonal than for multiyear ice, and more important for ponded than for snow-covered ice. Varying ice microstructure can obviously alter solar radiation transfer in the ice-ocean system, even with a constant ice thickness. Our results suggest that numerical models should take the variable microstructure of sea ice into account to improve model accuracy and to understand the interaction between internal variations in Arctic sea ice and the ocean, especially in summer.

Modelled variations of the inherent optical properties of summer Arctic ice and their effects on the radiation budget: A case based on ice cores from CHINARE 2008–2016

“…Many distributions are obtained in a cold laboratory, where the ice temperature is not consistent with that in the summer Arctic. As the refractive indices of brines and pure ice were similar, the distribution function of brine pockets had a smaller influence on the ice IOPs than gas bubbles (Yu et al, 2022). Here, we tentatively adjusted the exponent of the distribution function of the gas bubbles from its default value of -1.5 to -1, i.e., the fraction of small bubbles decreases, which coincides with warming ice https://doi.org/10.5194/egusphere-2022-552 Preprint.…”

“…Besides, Q abs and Q sca in the required size range are obtained using their effective radii, which are calculated according to Hansen & Travis (1974). The Delta-Eddington multiple scattering model, where the constant IOPs from Briegleb & Light (2007) were replaced by the modeled IOPs, was employed to estimate the apparent optical properties (AOPs: albedo αλ, tansmittance Tλ, and absorptivity Aλ) of the ice at the sampling sites (Yu et al, 2022). The broadband albedo (αB), transmittance (TB), and absorptivity (AB) were calculated by integrating the spectral values over band of the incident solar radiation, F0 as:…”

“…There are also differences in the IOPs of first-year ice because of different stages of melting (Veyssiè re et al, 2022). Yu et al (2022) carried out a study to investigate the sensitivity of ice IOPs on its microstructures, but they did not show how the ice IOPs change in the real world. Changes in ice microstructure and IOPs are especially important for the Arctic under the general warming climate and decreasing ice age.…”

Light Under Arctic Sea Ice in Observations and Earth System Models

“…For instance, pond fraction is considered, however, the light field also depends on melt pond distribution and geometry (Horvat et al, 2020). Possibly missing physics include the microstructure of snow (crystal size, specific surface area, see Warren, 1982Warren, , 2019 and ice (brine and gas inclusions, see Jin et al, 2022;Light et al, 2004;Warren, 2019;Yu et al, 2022). Snow-related issues may seem important, as the largest relative errors coincide with snow-covered ice.…”

Influence of New Parameterization Schemes on Arctic Sea Ice Simulation

“…It uses just radiation heat flux and temperature to compute sensible and latent heat flux directly. The IOP scheme [24] was developed to describe the effects of ice microstructure on inherent optical properties and used with the dEdd scheme to calculate the apparent optical properties of sea ice. The MPSD scheme [25] is used to determine the sub-grid melt pond size distribution after the melt pond fraction is calculated by melt pond schemes such as the LVL scheme.…”