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The magnitude, spectral composition, and variability of the Arctic sea ice surface albedo are key to understanding and numerically simulating Earth’s shortwave energy budget. Spectral and broadband albedos of Arctic sea ice were spatially and temporally sampled by on-ice observers along individual survey lines throughout the sunlit season (April–September, 2020) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The seasonal evolution of albedo for the MOSAiC year was constructed from spatially averaged broadband albedo values for each line. Specific locations were identified as representative of individual ice surface types, including accumulated dry snow, melting snow, bare and melting ice, melting and refreezing ponded ice, and sediment-laden ice. The area-averaged seasonal progression of total albedo recorded during MOSAiC showed remarkable similarity to that recorded 22 years prior on multiyear sea ice during the Surface Heat Budget of the Arctic Ocean (SHEBA) expedition. In accord with these and other previous field efforts, the spectral albedo of relatively thick, snow-free, melting sea ice shows invariance across location, decade, and ice type. In particular, the albedo of snow-free, melting seasonal ice was indistinguishable from that of snow-free, melting second-year ice, suggesting that the highly scattering surface layer that forms on sea ice during the summer is robust and stabilizing. In contrast, the albedo of ponded ice was observed to be highly variable at visible wavelengths. Notable temporal changes in albedo were documented during melt and freeze onset, formation and deepening of melt ponds, and during melt evolution of sediment-laden ice. While model simulations show considerable agreement with the observed seasonal albedo progression, disparities suggest the need to improve how the albedo of both ponded ice and thin, melting ice are simulated.
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Brighter Ocean: Arctic sea ice solar partitioning
This dataset contains the partitioning of the surface downwelling radiative fluxes by the Arctic sea ice by reflection, absorption, and transmission. The dataset covers the period from 1984 to 2022 and was provided on 25 km resolution on the NSIDC EASE2 grid. # Brighter Ocean: Arctic sea ice solar partitioning Dataset DOI: [10.5061/dryad.n02v6wxb5](https://doi.org/10.5061/dryad.n02v6wxb5) ## Description of the data and file structure Our focus is on the large-scale partitioning of the incident solar radiation between reflection to the atmosphere (albedo, *a*), absorption in the ice (absorptance, *A*) and transmission to the ocean (transmittance, *T*). These parameters were determined every day from 1984 to 2024 at every point on the Equal Area Scalable Earth 2.0 (EASE2) grid, within the sea ice extent boundary. The basis for the analysis relies on several satellite and model products. These include geophysical variables of shortwave radiation, surface melt and freeze onset dates, as well as sea ice concentration, age, and thickness. Sea ice albedo is estimated using a multiphase albedo evolution determined for first year ice (Perovich and Polashenski, 2012) and multiyear ice (Perovich et al., 2002; Light et al., 2022). Distinct albedo evolutions for first-year and multiyear sea ice are computed using Version 4 of the EASE-grid Sea Ice Age product by Tschudi et al. (2019). The dates of melt and freeze-up book-end the Arctic melt season and govern the seasonal evolution of surface albedo of sea ice. For the onset dates of continuous melt and continuous freeze, we use passive microwave retrievals at 25-km resolution produced by Markus et al. (2009). The ice concentration is a key parameter in determining the solar partitioning. We use passive microwave retrievals from the NASA Bootstrap algorithm (Comiso, 1986), which are available in the NOAA/NSIDC Climate Data Record (Meier et al., 2021). The product is provided at daily 25-km gridded resolutions. In some instances, temporal gaps in the data exist due to inconsistent satellite coverage. Transmittance through the ice is defined by an exponential decay law of the form and corrected for the near infrared light absorbed by the snow and ice and not transmitted. The correction ratio is estimated to vary from about 0.55 for clear skies to 0.62 for complete cloud cover. An average value of 0.58 is used in this study. The ice extinction coefficient for visible light. Based on field observations (Light et al., 2008, 2015), we use 1.0 m-1 for an ice cover dominated by bare ice (0.5 < *a~i~* < 0.7), 3.0 m-1 for a cover dominated by snow (*a~i~* > 0.7), and 0.7 m-1 for an ice cover dominated by melt ponds (*a~i~* < 0.5). *S*ea ice thickness and is determined using the simulated thickness from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) (Zhang and Rothrock, 2003). ### Files and variables #### File: BO_EASE2_gridded_25km_YYYY.nc **Description:** for year YYYY. **Variables:** dimensions: X = 263, Y = 263, time=365 or 366. insol (time,Y,X): surface downwelling solar radiative flux sic (time,Y,X): sea ice concentration sith (time,Y,X): sea ice thickness iceage (time,Y,X): sea ice age emelt, efreeze, fmelt, ffreeze (Y,X): Early ('e')/full ('f') melt/freeze onset date, in day-of-year. alb_yyy (time,Y,X): ice albedo using albedo scheme yyy. The albedo scheme include MYI (using multi-year ice scheme), FYI (using first-year ice scheme), and AGE (combined multi-year and first-year albedo depending on ice age). h_xxx_yyy (time,Y,X): heat flux on xxx surface type using albedo scheme yyy, with unit of W/m^2^. The xxx surface types include nIC (assuming fully ice covered), ice (ice portion of the gridbox), ocn (open water portion of the gridbox). The yyy albedo scheme include MYI (using multi-year ice scheme), FYI (using first-year ice scheme), and AGE (combined multi-year and first-year albedo depending on ice age). An exemption is h_ocn_SIC, the heat input to the open water portion of the gridbox using the sea ice concentration. accu_h_xxx_yyy (time,Y,X): the accumulated heat input into the gridbox, with unit of MJ/m^2^. hthr_ice_xxx_KAPPA0 (time,Y,X): the heat through ice portion of the gridbox, using albedo scheme xxx and constant ice extinction coefficient kappa of 1, with unit of W/m^2^. hthr_ice_xxx_KAPPA_ALB (time,Y,X): the heat through ice portion of the gridbox, using albedo scheme xxx and ice extinction coefficient kappa depending on ice albedo value, with unit of W/m^2^. accu_hthr_ice_xxx_KAPPA0 (time,Y,X): the accumulated heat through ice portion of the gridbox, using albedo scheme xxx and constant ice extinction coefficient kappa of 1, with unit of MJ/m^2^. accu_hthr_ice_xxx_KAPPA_ALB (time,Y,X): the accumulated heat through ice portion of the gridbox, using albedo scheme xxx and ice extinction coefficient kappa depending on ice albedo value, with unit of MJ/m^2^. ## Code/software The software for processing and analyze this dataset is published on Zenodo: [10.5281/zenodo.17675721](https://doi.org/10.5281/zenodo.17675721) The developmental package is hosted o GitHub: [https://github.com/liuzheng-arctic/BrighterOcean](https://github.com/liuzheng-arctic/BrighterOcean)
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- Award ID(s):
- 2325430
- PAR ID:
- 10677844
- Publisher / Repository:
- Dryad
- Date Published:
- Edition / Version:
- 12
- Subject(s) / Keyword(s):
- FOS: Earth and related environmental sciences FOS: Earth and related environmental sciences Arctic Ocean Sea ice Solar radiation
- Format(s):
- Medium: X Size: 28341289723 bytes
- Size(s):
- 28341289723 bytes
- Sponsoring Org:
- National Science Foundation
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