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Mixed-Phase Clouds Over the Southern Ocean as Observed From Satellite and Surface Based Lidar and Radar
Journal of Geophysical Research: Atmospheres ( IF 4.4 ) Pub Date : 2021-07-20 , DOI: 10.1029/2021jd034569
Gerald G. Mace 1 , Alain Protat 2, 3 , Sally Benson 1
Affiliation  

This study investigates the occurrence of mixed-phase clouds (MPC, i.e., cloud layers containing both liquid and ice water at sub-freezing temperatures) over the Southern Ocean (SO) using space- and surface-based lidar and radar observations. The occurrence of supercooled clouds is dominated by geometrically thin (<1 km) layers that rarely contain ice. We diagnose layers that are geometrically thicker than 1 km to contain ice ~65% and ~4% of the time from below by surface remote sensors and from above by orbiting remote sensors, respectively. We examine the discrepancy in MPC occurrence statistics as diagnosed from below and above the cloud layer. From above, we find that MPC occurrence has a gradient associated with the Antarctic Polar Front near 55°S with a rare occurrence of satellite-derived MPC south of that latitude. In contrast, surface sensors find ice in 33% of supercooled liquid water layers. We infer using observing system simulation experiments and data analysis that space-based lidar cannot identify the occurrence of MPC except when secondary ice-forming processes operate in convection that is, sufficiently strong to loft ice crystals to cloud tops. We conclude that the CALIPSO phase statistics of MPC have a severe low bias in MPC occurrence. Based on surface-based statistics in the SO, we present a parameterization of the frequency of MPC as a function of cloud top temperature that differs substantially from that used in recent climate model simulations.

中文翻译:

从卫星和地基激光雷达和雷达观测到的南大洋混合相云

本研究使用天基和地基激光雷达和雷达观测,调查了南大洋 (SO) 上空混合相云(MPC,即在低于冰点温度下含有液态和冰水的云层)的发生情况。过冷云的出现主要由极少包含冰的几何薄(<1 公里)层构成。我们分别通过地面遥感器和轨道遥感器从下方诊断出几何厚度超过 1 公里的冰层,其中包含约 65% 的冰层和约 4% 的时间。我们检查了从云层下方和上方诊断出的 MPC 发生统计数据的差异。从上面,我们发现 MPC 的发生具有与 55°S 附近的南极极锋相关的梯度,在该纬度以南很少发生卫星衍生的 MPC。相比之下,表面传感器在 33% 的过冷液态水层中发现了冰。我们通过观测系统模拟实验和数据分析推断,天基激光雷达无法识别 MPC 的发生,除非二次冰形成过程在对流中运行,即足够强以将冰晶吹到云顶。我们得出结论,MPC 的 CALIPSO 相位统计在 MPC 发生中具有严重的低偏差。基于 SO 中基于地表的统计数据,我们提出了 MPC 频率的参数化作为云顶温度的函数,这与最近的气候模型模拟中使用的有很大不同。我们通过观测系统模拟实验和数据分析推断,天基激光雷达无法识别 MPC 的发生,除非二次冰形成过程在对流中运行,即足够强以将冰晶吹到云顶。我们得出结论,MPC 的 CALIPSO 相位统计在 MPC 发生中具有严重的低偏差。基于 SO 中基于地表的统计数据,我们提出了 MPC 频率的参数化作为云顶温度的函数,这与最近的气候模型模拟中使用的有很大不同。我们通过观测系统模拟实验和数据分析推断,天基激光雷达无法识别 MPC 的发生,除非二次冰形成过程在对流中运行,即足够强以将冰晶吹到云顶。我们得出结论,MPC 的 CALIPSO 相位统计在 MPC 发生中具有严重的低偏差。基于 SO 中基于地表的统计数据,我们提出了 MPC 频率的参数化作为云顶温度的函数,这与最近的气候模型模拟中使用的有很大不同。
更新日期:2021-08-11
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