Global model reanalyses of temperature and radiation are used for many purposes because of their spatial and temporal homogeneity. However, they use sub-models for lakes that are smaller than the model grid. This paper compares the simplified small-lake model, known as FLake, used in the European Centre global reanalysis known as ERA5, with observations made in and near Lake Champlain in northern Vermont. Lake Champlain is a challenging test for the ERA5 FLake model. The lake, which extends over several grid cells, is the lowest region at 30 m above sea level within complex mountain topography. The smoothing of the adjacent mountain topography means that the ERA5 grid cells containing the lake have higher mean elevations then 30 m, and this contributes to a small cool bias in FLake mid-summer temperatures. The seasonal cycle of FLake temperatures has a sharper peak than the observed lake temperatures. In winter, lake temperatures are close to 3°C, while the 30 m deep FLake mixed layer (ML) is near freezing. In May and June, FLake maintains a deep ML, while lake profiles are generally strongly stratified with peak temperatures near the surface several degrees above the model ML. One possible contributing reason is that inflowing river temperatures that are not considered by FLake are as much as 5°C above the lake surface temperature from April to June. The lake does develop a ML structure as it cools from the temperature peak in August, but the FLake ML cools faster and grows deeper in fall. We conclude that the vertical mixing in the FLake ML is stronger than the vertical mixing in Lake Champlain.

中文翻译：

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ERA5 中尚普兰湖的 FLake 模型评估

温度和辐射的全球模型再分析因其空间和时间的均匀性而被用于许多目的。但是，他们对小于模型网格的湖泊使用子模型。本文将欧洲中心全球再分析 ERA5 中使用的简化小湖模型（称为 FLake）与佛蒙特州北部尚普兰湖及其附近的观测进行比较。尚普兰湖对 ERA5 FLake 模型来说是一项具有挑战性的测试。该湖横跨多个网格单元，是复杂山地地形中海拔 30 m 处的最低区域。相邻山地地形的平滑意味着包含该湖的 ERA5 网格单元的平均海拔高于 30 m，这导致 FLake 仲夏温度的小冷偏差。FLake 温度的季节性周期比观测到的湖泊温度具有更尖锐的峰值。冬季，湖泊温度接近 3°C，而 30 m 深的片状混合层 (ML) 接近结冰。在 5 月和 6 月，FLake 保持着较深的 ML，而湖泊剖面通常强烈分层，地表附近的峰值温度比模型 ML 高几度。一个可能的原因是 FLake 未考虑的流入河流温度比 4 月至 6 月的湖面温度高 5°C。该湖在从 8 月的温度峰值冷却时确实形成了 ML 结构，但 FLake ML 冷却速度更快，并且在秋季增长得更深。我们得出结论，FLake ML 中的垂直混合比尚普兰湖中的垂直混合更强。