Abstract Arctic tundra is undergoing a rapid transition due to global warming and will be exposed to snow-free conditions for longer periods under projected climate scenarios. Regional climate modeling is useful for understanding and predicting climate change in the Arctic tundra, however, the lack of in-situ observations of surface energy fluxes and the planetary boundary layer (PBL) structure hinders accurate predictions of local and regional climate around the Arctic. In this study, we investigate the performance of the Polar-optimized version of the Weather Research and Forecasting model (PWRF) in the Arctic tundra on clear days in summer. Based on simultaneous observations of surface fluxes and the PBL structure in Cambridge Bay, Nunavut, Canada, our validation shows that the PWRF simulates a drier environment, leading to a larger Bowen ratio and a warmer atmosphere compared to observations. Further sensitivity analyses indicate that the model biases are mainly from the uncertainties in physical parameters such as surface albedo and emissivity, the solar constant, and the model top height, rather than structural flaws in the model physics. Importantly, the PWRF reproduces the observations more accurately when the observed soil moisture is fed into the simulation. This indicates that there must be improvements in simulations of the land-atmosphere interaction at the Arctic tundra, not only in the accuracy of the initial soil moisture conditions but also in soil hydraulic properties and drainage processes. The mixing diagram analysis also shows that the entrainment process between the PBL and the overlying atmosphere needs to be improved for better weather and climate simulation. Our findings shed light on modeling studies in the Arctic region by disentangling the model error sources from uncertainties by parameters and physics package options.

中文翻译：

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夏季北极苔原极地 WRF 陆地-大气过程的评估

摘要 由于全球变暖，北极苔原正在经历快速转变，并且在预计的气候情景下将长时间暴露在无雪条件下。区域气候建模有助于理解和预测北极苔原的气候变化，但是，由于缺乏对地表能量通量和行星边界层 (PBL) 结构的现场观测，阻碍了对北极周围局部和区域气候的准确预测。在这项研究中，我们调查了极地优化版本的天气研究和预测模型 (PWRF) 在夏季晴朗的日子里在北极苔原上的性能。基于对加拿大努纳武特剑桥湾的表面通量和 PBL 结构的同时观察，我们的验证表明 PWRF 模拟了较干燥的环境，导致与观测相比更大的鲍温比和更温暖的大气。进一步的敏感性分析表明，模型偏差主要来自地表反照率和发射率、太阳常数、模型顶高等物理参数的不确定性，而非模型物理结构缺陷。重要的是，当将观测到的土壤水分输入到模拟中时，PWRF 会更准确地再现观测结果。这表明北极苔原陆地-大气相互作用的模拟必须有改进，不仅在初始土壤水分条件的准确性上，而且在土壤水力特性和排水过程中。混合图分析还表明，PBL 与上覆大气之间的夹带过程需要改进，以便更好地模拟天气和气候。我们的研究结果通过将模型误差源与参数和物理包选项的不确定性分开，为北极地区的建模研究提供了启示。