Effects of Arctic sea-ice concentration on turbulent surface fluxes in four atmospheric reanalyses

• Main Authors: Uhlíková, Tereza, Vihma, Timo, Karpechko, Alexey Yu, Uotila, Petteri Juha
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Arctic; Merra; Sea ice
• Online Access: https://doi.org/10.5194/egusphere-2023-1131; https://noa.gwlb.de/receive/cop_mods_00067602; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00066052/egusphere-2023-1131.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1131/egusphere-2023-1131.pdf

A prerequisite for understanding the local, regional, and hemispherical impacts of Arctic sea-ice decline on the atmosphere is to quantify the effects of sea-ice concentration (SIC) on the turbulent surface fluxes of sensible and latent heat in the Arctic. We analyse these effects utilising four global atmospheric reanalyses: ERA5, JRA-55, MERRA-2, and NCEP/CFSR (CFSR and CFSv2), and evaluate their uncertainties arising from inter-reanalysis differences in SIC and in the sensitivity of the turbulent surface fluxes to SIC. The magnitude of the differences in SIC is up to 0.15, but typically around 0.05 in most of the Arctic over all four seasons. Orthogonal-distance regression and ordinary-least-square regression analyses indicate that the greatest sensitivity of both the latent and the sensible heat flux to SIC occurs in the cold season, November to April. For these months, the average sensitivity is 400 W m-2 for the latent heat flux and over 800 W m-2 for the sensible heat flux per unit of SIC (change of SIC from 0 to 1), with the differences between reanalyses as large as 300 W m-2 for the latent heat flux and 600 W m-2 for the sensible heat flux per unit of SIC. The sensitivity is highest for the NCEP/CFSR reanalysis. Comparing the periods 1980–2000 and 2001–2021, we find that the effect of SIC on turbulent surface fluxes has weakened, owing to the increasing surface temperature of sea ice and the sea-ice decline. The results also indicate signs of decadal-scale improvement in the mutual agreement between reanalyses. The effect of SIC on turbulent surface fluxes arises mostly via the effect of SIC on atmosphere-surface differences in temperature and specific humidity, whereas the effect of SIC on wind speed partly cancels out in the turbulent surface fluxes, as the wind speed increases the magnitude of both upward and downward fluxes.