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Influence of Melt Ponds and Floe Size on Apparent Optical Properties of Sea Ice: An Idealized Modelling Investigation.

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Title: Influence of Melt Ponds and Floe Size on Apparent Optical Properties of Sea Ice: An Idealized Modelling Investigation.
Authors: Zhang, H.1 (AUTHOR), Yu, M.1 (AUTHOR), Lu, P.1 (AUTHOR) lupeng@dlut.edu.cn, Leppäranta, M.2 (AUTHOR), Cheng, B.3 (AUTHOR), Zhou, J.1 (AUTHOR), Wang, Q.1 (AUTHOR), Li, X.1 (AUTHOR), Li, Z.1 (AUTHOR)
Source: Journal of Geophysical Research. Oceans. Mar2025, Vol. 130 Issue 3, p1-20. 20p.
Subject Terms: *Albedo, *Water levels, *Sea ice, Ice floes, Monte Carlo method, Zone melting
Abstract: Melt ponds are usually modeled for light transfer as horizontally infinite water layers on level ice, and the albedo of floe is determined by a linear combination (LC) of melt pond and bare ice albedos weighted by their areal coverages. However, this method does not reflect the actual conditions because ice floes have a limited size. In the present study, an idealized two‐dimensional Monte Carlo (MC) model was employed to investigate the influence of melt ponds and floe size on the apparent optical properties (AOPs) of summer sea ice. The results showed that the albedo and vertical light transmittance of large floes mainly depend on the melt pond fraction and ice thickness, which is consistent to previous results. However, also the floe size plays an important role in the AOPs of small floes. Two parameters were proposed to present the accuracy of the LC method for small floes with lower sea ice concentration: the ratios of sea ice albedo and transmittance determined by the LC (αline,Tline) to the values in the MC model (α, T), Kα = αline/α, and KT = Tline/T, respectively. Due to the lateral transmittance, Kα, KT ≥ 1 and asymptotically approach 1 with floe size increasing to infinity. To reduce the biases in albedo and transmittance due to floe size, new parameterization formulas were provided for Kα and KT with the distance into the marginal ice zone and in different melting stages. The results have potential to be implemented into future sea ice models to correct the AOPs of small sea ice floes obtained via the LC method. Plain Language Summary: A two‐dimensional Monte Carlo model was developed to examine the influence of melt ponds and floe size on the AOPs of the summer sea ice. The results argue that the horizontal size of melt ponds and ice floes pose a very important impact on the ice surface albedo that cannot be ignored in sea ice modeling, especially in the marginal ice zone containing many small floes with lower sea ice concentration. A parameterization scheme to correct the overestimation in floe surface albedo by using the linear combination (LC) method is also proposed, which has potential to be implemented into future numerical models of sea ice. The accuracy of both the plane‐parallel assumption and the LC method were first evaluated, which have been widely employed as determining the AOPs of melt ponds and summer sea ice floes in numerical modeling. Key Points: A Monte Carlo model is developed to explore the influence of melt pond and floe size on apparent optical properties (AOPs) of sea iceThe lateral transmittance of floes causes errors in plane‐parallel assumption and the linear combination (LC) method in modeling the albedoA parameterization scheme is proposed to correct the floe surface albedo calculated by LC with a diameter less than 20 m [ABSTRACT FROM AUTHOR]
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Description
Abstract:Melt ponds are usually modeled for light transfer as horizontally infinite water layers on level ice, and the albedo of floe is determined by a linear combination (LC) of melt pond and bare ice albedos weighted by their areal coverages. However, this method does not reflect the actual conditions because ice floes have a limited size. In the present study, an idealized two‐dimensional Monte Carlo (MC) model was employed to investigate the influence of melt ponds and floe size on the apparent optical properties (AOPs) of summer sea ice. The results showed that the albedo and vertical light transmittance of large floes mainly depend on the melt pond fraction and ice thickness, which is consistent to previous results. However, also the floe size plays an important role in the AOPs of small floes. Two parameters were proposed to present the accuracy of the LC method for small floes with lower sea ice concentration: the ratios of sea ice albedo and transmittance determined by the LC (αline,Tline) to the values in the MC model (α, T), Kα = αline/α, and KT = Tline/T, respectively. Due to the lateral transmittance, Kα, KT ≥ 1 and asymptotically approach 1 with floe size increasing to infinity. To reduce the biases in albedo and transmittance due to floe size, new parameterization formulas were provided for Kα and KT with the distance into the marginal ice zone and in different melting stages. The results have potential to be implemented into future sea ice models to correct the AOPs of small sea ice floes obtained via the LC method. Plain Language Summary: A two‐dimensional Monte Carlo model was developed to examine the influence of melt ponds and floe size on the AOPs of the summer sea ice. The results argue that the horizontal size of melt ponds and ice floes pose a very important impact on the ice surface albedo that cannot be ignored in sea ice modeling, especially in the marginal ice zone containing many small floes with lower sea ice concentration. A parameterization scheme to correct the overestimation in floe surface albedo by using the linear combination (LC) method is also proposed, which has potential to be implemented into future numerical models of sea ice. The accuracy of both the plane‐parallel assumption and the LC method were first evaluated, which have been widely employed as determining the AOPs of melt ponds and summer sea ice floes in numerical modeling. Key Points: A Monte Carlo model is developed to explore the influence of melt pond and floe size on apparent optical properties (AOPs) of sea iceThe lateral transmittance of floes causes errors in plane‐parallel assumption and the linear combination (LC) method in modeling the albedoA parameterization scheme is proposed to correct the floe surface albedo calculated by LC with a diameter less than 20 m [ABSTRACT FROM AUTHOR]
ISSN:21699275
DOI:10.1029/2024JC021434