Modelling radiative transfer through ponded first-year Arctic sea ice with a plane-parallel model

Taskjelle, Torbjørn; Hudson, Stephen R.; Granskog, Mats A.; Hamre, Børge

doi:10.5194/tc-11-2137-2017

Cited by 12 publications

(14 citation statements)

References 39 publications

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“…At the ice bottom, the effect of a different transmittance can be seen within a distance of 2–3 times the ice thickness [ Ehn et al ., ; Petrich et al ., ]. A plane parallel model is not able to capture such effects due to its 1‐D nature [ Taskjelle et al ., ]. Hence, while what happens immediately below the ice is likely well captured by AccuRT except for very close to the boundary between surface types, the discussion of what happens further down the water column may only be valid some longer distance from ice with notably different transmittance.…”

Section: Resultsmentioning

confidence: 99%

“…In situ profiles of optical properties were made from a heated tent established on the sea ice several hundred meters away from the ship. Profiles of absorption and attenuation coefficients were measured with two different instruments during the drifts of both Floes 3 and 4 [ Taskjelle et al ., ; Pavlov et al ., ]. An a‐Sphere (HOBI Labs, USA) measured absorption ( a (λ), excluding absorption by pure water) between 350 and 750 nm at 1 nm resolution, and an ac‐9 (WET Labs, Philomath, OR, USA) measured absorption ( a (λ), excluding absorption by pure water) and beam attenuation ( c (λ), excluding attenuation by pure water), which is a sum of absorption and scattering at nine distinct wavelengths: 412, 440, 488, 510, 532, 555, 650, 676, and 715 nm (see full list of symbols and units in Table ).…”

Section: Methodsmentioning

confidence: 99%

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Altered inherent optical properties and estimates of the underwater light field during an Arctic under‐ice bloom of Phaeocystis pouchetii

et al. 2017

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In spring 2015, we observed an extensive phytoplankton bloom of Phaeocystis pouchetii, with chlorophyll a concentrations up to 7.5 mg m−3, under compact snow‐covered Arctic sea ice at 80–81°N during the Norwegian young sea ICE (N‐ICE2015) expedition. We investigated the influence of the under‐ice bloom on inherent optical properties (IOPs) of the upper ocean. Absorption and scattering in the upper 20 m of the water column at visible wavebands increased threefold and tenfold, respectively, relative to prebloom conditions. The scattering‐to‐absorption ratio during the Phaeocystis under‐ice bloom was higher than in previous Arctic studies investigating diatom blooms. During the bloom, absorption by colored dissolved organic matter (at 375 nm), seemingly of autochthonous origin, doubled. Total absorption by particles (at 440 nm), dominated by phytoplankton (>90%), increased tenfold. Measured absorption and scattering in the water were used as inputs for a 1D coupled atmosphere‐ice‐ocean radiative transfer model (AccuRT) to investigate effects of altered IOPs on the under‐ice light field. Multiple scattering between sea ice and phytoplankton in the ocean led to an increase in scalar irradiance in the photosynthetically active radiation range (Eo(PAR)) at the ice‐ocean interface by 6–7% compared to prebloom situation. This increase could have a positive feedback on ice‐algal and under‐ice phytoplankton productivity. The ratio between Eo(PAR) and downwelling planar irradiance (Ed(PAR)) below sea ice reached 1.85. Therefore, the use of Ed(PAR) might significantly underestimate the amount of PAR available for photosynthesis underneath sea ice. Our findings could help to improve light parameterizations in primary production models.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Altered inherent optical properties and estimates of the underwater light field during an Arctic under‐ice bloom of Phaeocystis pouchetii

et al. 2017

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“…The present RTM treats the ice lid, pond water, and underlying ice as parallel layers with uniform IOPs in each layer, which is valid for thin level ice that typically has large and shallow ponds (Webster et al, ). In situ measurements on melt ponds were affected more or less by the uneven pond bottom, and the contrasts at the boundary between ponded and bare ice (Taskjelle et al, ). It departs from the definition of the RTM and contributes to a higher surface albedo in measurements as comparing with the results of the parallel‐layered model.…”

Section: Discussionmentioning

confidence: 99%

Impact of a Surface Ice Lid on the Optical Properties of Melt Ponds

et al. 2018

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To investigate the influence of a surface ice lid on the optical properties of a melt pond, a radiative transfer model was employed that includes four plane‐parallel layers: an ice lid, a melt pond, the underlying ice, and the ocean beneath the ice. The thickness Hs and the scattering coefficient σs of the ice lid are altered. Variations in the spectral albedo αλ and transmittance Tλ due to Hs for a transparent ice lid are limited, and scattering in the ice lid has a pronounced impact on the albedo of melt ponds as well as the vertical distribution of spectral irradiance in ponded sea ice. The thickness of the ice lid determines the amount of solar energy absorbed. A 2‐cm‐thick ice lid can absorb 13% of the incident solar energy, half of the energy absorbed by a 30‐cm‐deep meltwater layer below the lid. This has an influence on the thermodynamics of melting sea ice. The color and spectral albedo of refreezing melt ponds depend on the value of the dimensionless number σs·Hs. Good agreement between field measurements and our model simulations is found. The number σs·Hs is confirmed to be a good index showing that the influence of an ice lid with σs·Hs < 0.5 is negligible. This criterion can be easily performed during field observations through visually judging whether the ice lid has significantly changed the color of liquid melt ponds or not.

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“…Account was taken of the spectral nature of the problem; however to maintain consistency between the treatment of snow and blue ice the optical properties were linked to effective grain size and a spectral extinction coefficient was calculated on this basis. We also note related studies that investigated the spectral albedo of white sea ice or snow, but not the internal radiative field (Malinka et al, 2016;Gardner andSharp, 2010, Ehn et al, 2011;Taskjelle et al, 2017), or considered internal scattering from a purely theoretical perspective (Malinka, 2014).…”

Section: Introductionmentioning

confidence: 91%

Solar radiative transfer in Antarctic blue ice: spectral considerations, subsurface enhancement, and inclusions

Smedley

Evatt

Mallinson

et al. 2019

Preprint

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Abstract. We describe and validate a Monte Carlo model to track photons over the full range of solar wavelengths as they travel into optically thick Antarctic blue ice. The model considers both reflection and transmission of radiation at the surface of blue ice, scattering by air bubbles within it and spectral absorption due to the ice. The ice surface is treated as planar whilst bubbles are considered as spherical scattering centres using the Henyey-Greenstein approximation. Using bubble radii and number concentrations that are representative of Antarctic blue ice, we calculate spectral albedos and spectrally-integrated downwelling and upwelling radiative fluxes as functions of depth and find that, relative to the incident irradiance, there is a marked subsurface enhancement in the downwelling flux and accordingly also in the mean irradiance. This is due to the interaction between the refractive air-ice interface and the scattering interior and is particularly notable at blue and UV wavelengths which correspond to the minimum of the absorption spectrum of ice. In contrast the absorption path length at IR wavelengths is short and consequently the attenuation is more complex than can be described by a simple Lambert-Beer style exponential decay law – instead we present a triple exponential fit to the net irradiance against depth. We find that there is a moderate dependence on the solar zenith angle and surface conditions such as altitude and cloud optical depth. For macroscopic absorbing inclusions we observe both geometry- and size-dependent self-shadowing that reduces the fractional irradiance incident on an inclusion's surface. Despite this, the inclusions act as local photon sinks and are subject to fluxes that are several times the magnitude of the single scattering contribution. Such enhancement may have consequences for the energy budget in regions of the cryosphere where particulates are present near the surface. These results also have particular relevance to measurements of the internal radiation field: account must be taken of both self-shadowing and the optical effect of introducing the detector.

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Modelling radiative transfer through ponded first-year Arctic sea ice with a plane-parallel model

Cited by 12 publications

References 39 publications

Altered inherent optical properties and estimates of the underwater light field during an Arctic under‐ice bloom of Phaeocystis pouchetii

Altered inherent optical properties and estimates of the underwater light field during an Arctic under‐ice bloom of Phaeocystis pouchetii

Impact of a Surface Ice Lid on the Optical Properties of Melt Ponds

Solar radiative transfer in Antarctic blue ice: spectral considerations, subsurface enhancement, and inclusions

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