Mitchell David L, Garnier Anne, Pelon Jacques, Erfani Ehsan
Desert Research Institute, Reno, 89512-1095, USA.
Science Systems and Applications, Inc., Hampton, Virginia, USA.
Atmos Chem Phys. 2018;18(23):17325-17354. doi: 10.5194/acp-18-17325-2018. Epub 2018 Dec 6.
A new satellite remote sensing method is described whereby the sensitivity of thermal infrared wave resonance absorption to small ice crystals is exploited to estimate cirrus cloud ice particle number concentration N, effective diameter D, and ice water content IWC. This method uses co-located observations from the Infrared Imaging Radiometer (IIR) and from the CALIOP () lidar aboard the CALIPSO ( polar orbiting satellite, employing IIR channels at 10.6 μm and 12.05 μm. Using particle size distributions measured over several flights of the TC4 (Tropical Composition, Cloud and Climate Coupling) and the mid-latitudes SPARTICUS (Small Particles in Cirrus) field campaigns, we show for the first time that N/IWC is tightly related to β; the ratio of effective absorption optical depths at 12.05 μm and 10.6 μm. Relationships developed from in situ aircraft measurements are applied to β derived from IIR measurements to retrieve N. This satellite remote sensing method is constrained by measurements of β from the IIR and is by essence sensitive to the smallest ice crystals. Retrieval uncertainties are discussed, including uncertainties related to in situ measurement of small ice crystals (D < 15 µm), which are studied through comparisons with IIR β. The method is applied here to single-layered semi-transparent clouds having a visible optical depth between about 0.3 and 3, where cloud base temperature is ≤ 235 K. Two years of CALIPSO data have been analyzed for the years 2008 and 2013, with the dependence of cirrus cloud N and D on altitude, temperature, latitude, season (winter vs. summer) and topography (land vs. ocean) described. The results for the mid-latitudes show a considerable dependence on season. In the high latitudes, N tends to be highest and D smallest, whereas the opposite is true for the tropics. The frequency of occurrence of these relatively thick cirrus clouds exhibited a strong seasonal dependence in the high latitudes, with the occurrence frequency during Arctic winter being at least twice that of any other season. Processes that could potentially explain some of these micro-and macroscopic cloud phenomena are discussed.
本文描述了一种新的卫星遥感方法，该方法利用热红外波共振吸收对小冰晶的敏感性来估算卷云冰粒子数浓度N、有效直径D和冰水含量IWC。此方法使用了来自红外成像辐射计（IIR）和搭载在CALIPSO（极地轨道卫星）上的CALIOP激光雷达的同步观测数据，采用了10.6μm和12.05μm的IIR通道。利用在TC4（热带成分、云和气候耦合）和中纬度地区SPARTICUS（卷云中的小粒子）几次飞行中测量的粒子尺寸分布，我们首次表明N/IWC与β紧密相关；β是12.05μm和10.6μm处有效吸收光学深度的比值。将从飞机原位测量得出的关系应用于从IIR测量得出的β，以反演N。这种卫星遥感方法受到IIR对β测量的限制，本质上对最小的冰晶敏感。讨论了反演不确定性，包括与小冰晶（D < 15μm）原位测量相关的不确定性，通过与IIRβ的比较对其进行了研究。该方法在此应用于可见光光学深度约为0.3至3、云底温度≤235K的单层半透明云。分析了2008年和2013年两年的CALIPSO数据，描述了卷云N和D对海拔、温度、纬度、季节（冬季与夏季）和地形（陆地与海洋）的依赖性。中纬度地区的结果显示出对季节的显著依赖性。在高纬度地区，N往往最高而D最小，而在热带地区则相反。这些相对较厚卷云的出现频率在高纬度地区表现出强烈的季节依赖性，北极冬季的出现频率至少是其他任何季节的两倍。讨论了可能解释其中一些微观和宏观云现象的过程。
