Twomey effect observed from collocated microphysical and remote sensing measurements over shallow cumulus
Twomey effect observed from collocated microphysical and remote sensing measurements over shallow cumulus
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DOI：
10.1002/2013jd020131
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发表时间：
2014-02
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通讯作者：
F. Werner;F. Ditas;H. Siebert;M. Simmel;B. Wehner;P. Pilewskie;T. Schmeissner;R. Shaw;S. Hartmann
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文献类型：
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作者：
F. Werner;F. Ditas;H. Siebert;M. Simmel;B. Wehner;P. Pilewskie;T. Schmeissner;R. Shaw;S. Hartmann
给出了巴巴多斯附近浅层信风积云的图米效应的明显实验证据。从直升机载光谱云反射辐射测量中反演的有效液滴半径(REF)和云光学厚度(τ)以及光谱云反射率(γλ)与来自云下层(N)的气溶胶颗粒数浓度的配置现场观测相关联。N表示直径大于80 nm的颗粒的浓度，并且表示处于激活模式的颗粒。利用机载云湍流观测系统(ACTOS)现场采集了云微物理参数和气溶胶参数。光谱云反射辐射数据由光谱模块化航空辐射测量系统(SMART-HELIOS)采集。随着N的增加，τ和γλ的概率密度函数向更大的值移动，而反演的REF的平均值和观测范围减小。对于液水路径恒定的料箱，推导了Reff、τ和γλ对N的相对磁化率(RS)。对于Reff和τ，RS的结果值在0.35的范围内，对于γλ，RS的值在0.27的范围内。这些结果接近理论上可能的最大极化率。总体而言，巴巴多斯附近采集的浅层积云显示出均匀的、平面平行的云的特征。由现场测量的Reff得到的RS与从微物理地块模型得到的RS的比较是非常一致的。
Clear experimental evidence of the Twomey effect for shallow trade wind cumuli near Barbados is presented. Effective droplet radius (reff) and cloud optical thickness (τ), retrieved from helicopter‐borne spectral cloud‐reflected radiance measurements, and spectral cloud reflectivity (γλ) are correlated with collocated in situ observations of the number concentration of aerosol particles from the subcloud layer (N). N denotes the concentration of particles larger than 80 nm in diameter and represents particles in the activation mode. In situ cloud microphysical and aerosol parameters were sampled by the Airborne Cloud Turbulence Observation System (ACTOS). Spectral cloud‐reflected radiance data were collected by the Spectral Modular Airborne Radiation measurement sysTem (SMART‐HELIOS). With increasing N a shift in the probability density functions of τ and γλ toward larger values is observed, while the mean values and observed ranges of retrieved reff decrease. The relative susceptibilities (RS) of reff, τ, and γλ to N are derived for bins of constant liquid water path. The resulting values of RS are in the range of 0.35 for reff and τ, and 0.27 for γλ. These results are close to the maximum susceptibility possible from theory. Overall, the shallow cumuli sampled near Barbados show characteristics of homogeneous, plane‐parallel clouds. Comparisons of RS derived from in situ measured reff and from a microphysical parcel model are in close agreement.