The Iceland and Greenland Seas are a crucial region for the climate system, being the headwaters of the lower limb of the Atlantic Meridional Overturning Circulation. Investigating the atmosphere–ocean–ice processes in this region often necessitates the use of meteorological reanalyses—a representation of the atmospheric state based on the assimilation of observations into a numerical weather prediction system. Knowing the quality of reanalysis products is vital for their proper use. Here we evaluate the surface‐layer meteorology and surface turbulent fluxes in winter and spring for the latest reanalysis from the European Centre for Medium‐Range Weather Forecasts, i.e., ERA5. In situ observations from a meteorological buoy, a research vessel, and a research aircraft during the Iceland–Greenland Seas Project provide unparalleled coverage of this climatically important region. The observations are independent of ERA5. They allow a comprehensive evaluation of the surface meteorology and fluxes of these subpolar seas and, for the first time, a specific focus on the marginal ice zone. Over the ice‐free ocean, ERA5 generally compares well to the observations of surface‐layer meteorology and turbulent fluxes. However, over the marginal ice zone, the correspondence is noticeably less accurate: for example, the root‐mean‐square errors are significantly higher for surface temperature, wind speed, and surface sensible heat flux. The primary reason for the difference in reanalysis quality is an overly smooth sea‐ice distribution in the surface boundary conditions used in ERA5. Particularly over the marginal ice zone, unrepresented variability and uncertainties in how to parameterize surface exchange compromise the quality of the reanalyses. A parallel evaluation of higher‐resolution forecast fields from the Met Office's Unified Model corroborates these findings.

中文翻译：

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ERA5再分析中对冰岛和格陵兰海的地表气象和通量的评估：海冰分布的影响

冰岛和格陵兰海是气候系统的关键区域，是大西洋子午线翻转环流下肢的源头。调查该地区的大气-海冰过程通常需要使用气象再分析，这是将观测值同化为数值天气预报系统一样的大气状态表示。了解重新分析产品的质量对于正确使用它们至关重要。在这里，我们评估了冬季和春季的表层气象学和地表湍流，以获取欧洲中距离天气预报中心（ERA5）的最新再分析。气象浮标，研究船的实地观测，冰岛－格陵兰海洋项目期间的一架研究飞机为这一气候重要地区提供了无与伦比的覆盖范围。观察结果独立于ERA5。它们允许对这些亚极海的表面气象学和通量进行全面评估，并且首次特别关注边缘冰区。在无冰的海洋上，ERA5通常可以与表层气象学和湍流通量的观测结果进行比较。但是，在边缘冰带上，对应关系的准确性明显较差：例如，表面温度，风速和表面显热通量的均方根误差明显更高。重新分析质量差异的主要原因是ERA5中使用的表面边界条件下的海冰分布过于平滑。特别是在边缘冰区，如何参数化地表交换的不确定性和不确定性影响了再分析的质量。大都会办公室统一模型对高分辨率预报领域的平行评估证实了这些发现。