Cloud Phase and Relative Humidity Distributions over the Southern Ocean in Austral Summer Based on In Situ Observations and CAM5 Simulations
Cloud Phase and Relative Humidity Distributions over the Southern Ocean in Austral Summer Based on In Situ Observations and CAM5 Simulations
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DOI：
10.1175/jcli-d-18-0232.1
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发表时间：
2019-05-01
影响因子：
4.9
通讯作者：
Stephens, Britton B.
中科院分区：
文献类型：
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作者：
D'Alessandro, John J.;Diao, Minghui;Stephens, Britton B.
通过现场观测和全球气候模拟，比较了南半球夏季南大洋上空-67℃到0℃的云相和相对湿度的分布。使用0.1到50公里的水平平均观测值进行尺度感知比较。水平分辨率对云相频率、相对湿度分布和液体质量分数的影响小于液体和冰水含量(分别为LWC和IWC)、液体和冰数浓度(分别为Nc(Liq)和Nc(冰))和冰过饱和(ISS)频率。在-10摄氏度到0摄氏度，观测显示液体和混合相的比例分别为27%-34%和17%-37%，而模拟结果分别为60%-70%和3%-4%。模拟高估(低估)了液态(混合)相的LWC和Nc(Liq)，高估了混合相的Nc(冰)，低估(高估)了冰和混合相的IWC，低估(高估)了低于(高于)-5℃的液体质量分数，表明不同的云相需要观测约束。在所有数据集中，液体和混合相中的相对湿度经常出现在液体饱和时，但在-20℃到0℃之间，观测到的冰相相对湿度与液体饱和度的偏差可能高达20%-40%，这表明对于低液体质量分数(
Cloud phase and relative humidity (RH) distributions at -67 degrees to 0 degrees C over the Southern Ocean during austral summer are compared between in situ airborne observations and global climate simulations. A scale-aware comparison is conducted using horizontally averaged observations from 0.1 to 50 km. Cloud phase frequencies, RH distributions, and liquid mass fraction are found to be less affected by horizontal resolutions than liquid and ice water content (LWC and IWC, respectively), liquid and ice number concentrations (Nc(liq) and Nc(ice), respectively), and ice supersaturation (ISS) frequency. At -10 degrees to 0 degrees C, observations show 27%-34% and 17%-37% of liquid and mixed phases, while simulations show 60%-70% and 3%-4%, respectively. Simulations overestimate (underestimate) LWC and Nc(liq) in liquid (mixed) phase, overestimate Nc(ice) in mixed phase, underestimate IWC in ice and mixed phases, and underestimate (overestimate) liquid mass fraction below (above) -5 degrees C, indicating that observational constraints are needed for different cloud phases. RH frequently occurs at liquid saturation in liquid and mixed phases for all datasets, yet the observed RH in ice phase can deviate from liquid saturation by up to 20%-40% at -20 degrees to 0 degrees C, indicating that the model assumption of liquid saturation for coexisting ice and liquid is inaccurate for low liquid mass fractions (