This study uses cloud and radiative properties collected from in situ and remote sensing instruments during two coordinated campaigns over the Southern Ocean between Tasmania and Antarctica in January–February 2018 to evaluate the simulations of clouds and precipitation in nudged‐meteorology simulations with the CAM6 and AM4 global climate models sampled at the times and locations of the observations. Fifteen SOCRATES research flights sampled cloud water content, cloud droplet number concentration, and particle size distributions in mixed‐phase boundary layer clouds at temperatures down to −25°C. The 6‐week CAPRICORN2 research cruise encountered all cloud regimes across the region. Data from vertically pointing 94 GHz radars deployed was compared with radar simulator output from both models. Satellite data were compared with simulated top‐of‐atmosphere (TOA) radiative fluxes. Both models simulate observed cloud properties fairly well within the variability of observations. Cloud base and top in both models are generally biased low. CAM6 overestimates cloud occurrence and optical thickness while cloud droplet number concentrations are biased low, leading to excessive TOA reflected shortwave radiation. In general, low clouds in CAM6 precipitate at the same frequency but are more homogeneous compared to observations. Deep clouds are better simulated but produce snow too frequently. AM4 underestimates cloud occurrence but overestimates cloud optical thickness even more than CAM6, causing excessive outgoing longwave radiation fluxes but comparable reflected shortwave radiation. AM4 cloud droplet number concentrations match observations better than CAM6. Precipitating low and deep clouds in AM4 have too little snow. Further investigation of these microphysical biases is needed for both models.

中文翻译：

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利用南大洋观测资料评估CAM6和AM4中的云层和降水模拟

这项研究使用了在塔斯马尼亚岛和南极洲之间于2018年1月至2月在南大洋进行的两次协调运动中从现场和遥感仪器收集的云和辐射特性，以评估利用CAM6和AM4进行的轻推气象模拟中的云和降水模拟在观测时间和地点采样的全球气候模型。十五次SOCRATES研究飞行在低至-25°C的温度下对混合相边界层云中的云水含量，云滴数浓度和粒径分布进行了采样。为期6周的CAPRICORN2研究航行遇到了该地区的所有云状况。将来自部署的垂直指向的94 GHz雷达的数据与两个模型的雷达模拟器输出进行了比较。将卫星数据与模拟的大气层顶（TOA）辐射通量进行了比较。两种模型都在观测值的变异性内很好地模拟了观测到的云特性。两种模型的云底和云顶通常偏低。CAM6高估了云的出现和光学厚度，而云滴数浓度偏低，导致TOA反射的短波辐射过多。通常，CAM6中的低云以相同的频率沉淀，但与观测值相比更加均匀。可以更好地模拟深云，但会经常下雪。AM4低估了云的发生，但比CAM6高估了云的光学厚度，从而导致过多的长波辐射通量，但反射的短波辐射却相当。AM4云滴数量浓度比CAM6更好地符合观察结果。在AM4中，低云和深云的降雨很少。这两个模型都需要进一步研究这些微物理偏差。