Evaluation of Six Atmospheric Reanalyses over Arctic Sea Ice from Winter to Early Summer

• Published in: Journal of Climate
• Main Authors: Graham, Robert, Cohen, Lana, Ritzhaupt, Nicole, Segger, Benjamin, Graversen, Rune, Rinke, Anette, Walden, Von P., Granskog, Mats, Hudson, Stephen
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2019
• Subjects: VDP::Mathematics and natural science: 400; VDP::Matematikk og Naturvitenskap: 400; Arctic; Merra; Svalbard; Sea ice
• Online Access: https://hdl.handle.net/10037/17426; https://doi.org/10.1175/JCLI-D-18-0643.1

© Copyright 19 June 2019 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. All AMS journals and monograph publications are registered with the Copyright Clearance Center ( http://www.copyright.com ). Questions about permission to use materials for which AMS holds the copyright can also be directed to [e-mail]. Additional details are provided in the AMS Copyright Policy statement, available on the AMS website ( http://www.ametsoc.org/CopyrightInformation ). This study evaluates the performance of six atmospheric reanalyses (ERA-Interim, ERA5, JRA-55, CFSv2, MERRA-2, and ASRv2) over Arctic sea ice from winter to early summer. The reanalyses are evaluated using observations from the Norwegian Young Sea Ice campaign (N-ICE2015), a 5-month ice drift in pack ice north of Svalbard. N-ICE2015 observations include surface meteorology, vertical profiles from radiosondes, as well as radiative and turbulent heat fluxes. The reanalyses simulate surface analysis variables well throughout the campaign, but have difficulties with most forecast variables. Wintertime (January–March) correlation coefficients between the reanalyses and observations are above 0.90 for the surface pressure, 2-m temperature, total column water vapor, and downward longwave flux. However, all reanalyses have a positive wintertime 2-m temperature bias, ranging from 1° to 4°C, and negative (i.e., upward) net longwave bias of 3–19 W m −2 . These biases are associated with poorly represented surface inversions and are largest during cold-stable periods. Notably, the recent ERA5 and ASRv2 datasets have some of the largest temperature and net longwave biases, respectively. During spring (April–May), reanalyses fail to simulate observed persistent cloud layers. Therefore they overestimate the net shortwave flux (5–79 W m −2 ) and underestimate the net longwave flux (8–38 W m −2 ). Promisingly, ERA5 provides the best estimates of downward radiative fluxes in spring and summer, suggesting improved forecasting of Arctic cloud cover. All reanalyses exhibit large negative (upward) residual heat flux biases during winter, and positive (downward) biases during summer. Turbulent heat fluxes over sea ice are simulated poorly in all seasons.