New airborne retrieval approach for trade wind cumulus properties under overlying cirrus
New airborne retrieval approach for trade wind cumulus properties under overlying cirrus
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DOI：
10.1002/jgrd.50334
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发表时间：
2013-05
期刊：
影响因子：
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通讯作者：
F. Werner;H. Siebert;P. Pilewskie;T. Schmeissner;R. Shaw;M. Wendisch
中科院分区：
文献类型：
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作者：
F. Werner;H. Siebert;P. Pilewskie;T. Schmeissner;R. Shaw;M. Wendisch
提出了一种新的反演浅积云光学厚度τ和有效液滴半径Reff的方法。这种新的方法允许在没有覆盖卷云的微物理和光学属性的先验知识的情况下进行检索。这种反演适用于巴巴多斯附近的信风积云上方的光谱模块化航空辐射测量系统(SMART-HELIOS)收集的直升机上的太阳光谱反射率测量。通过安装在机载云湍流观测系统(ACTOS)上的现场仪器，测量了配置的微物理积云特性(液态水含量、有效液滴半径、液滴数浓度)。云的不均匀性导致对检索到的τ的低估高达114%，而Reff的偏差高达27%。此外，对上覆卷云的错误描述可能会导致对经典提取的积云Reff的高估高达50%，而对τ的低估高达6%。新的反演有效地校正了覆盖卷云的影响，使得能够可靠地估计光学薄的、阴天的卷云条件下的积云的τ，并将积云的Reff的反演误差降低近50%。现场实测值与反演值的一致性在±1μm范围内，并能较大范围地再现由于不同飞行日的气溶胶负荷和云顶高度不同而产生的大范围的实测值(7-18μm)。观测到的τ范围在5到36之间。
A new retrieval method is presented to derive the optical thickness τ and effective droplet radius reff of shallow cumulus in the presence of overlying thin cirrus. This new approach allows for a retrieval without a priori knowledge of the microphysical and optical properties of the overlying cirrus. The retrieval is applied to helicopter‐borne solar spectral reflectivity measurements gathered by the Spectral Modular Airborne Radiation measurements sysTem (SMART‐HELIOS) above trade wind cumuli near Barbados. Collocated microphysical cumulus properties (liquid water content, effective droplet radius, droplet number concentration) were measured by in situ instruments installed on the Airborne Cloud Turbulence Observation System (ACTOS). Cloud inhomogeneities lead to an underestimation of retrieved τ of up to 114%, while reff is biased by up to 27%. Moreover, misrepresentation of the overlying cirrus may cause an overestimation of the classically retrieved cumulus reff of up to 50% and an underestimation of τof up to 6%. The new retrieval, effectively correcting for the influence of overlying cirrus, enables reliable estimates of τ of the cumuli for optically thin, overcast cirrus conditions and reduces the retrieval error for reff of the cumuli by almost 50%. Agreement between in situ measured and retrieved reff is in the range of ±1 μm. The retrieval can also reproduce the wide range of in situ measured mean reff (7–18 μm), which is a result of different aerosol load and cloud top heights on the different flight days. The observed τ ranges between 5 and 36.