Estimating the direct radiative effect of absorbing aerosols overlying marine boundary layer clouds in the southeast Atlantic using MODIS and CALIOP
Estimating the direct radiative effect of absorbing aerosols overlying marine boundary layer clouds in the southeast Atlantic using MODIS and CALIOP
复制标题
使用 MODIS 和 CALIOP 估计东南大西洋海洋边界层云上吸收气溶胶的直接辐射效应
DOI：
10.1002/jgrd.50449
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Dongmin Lee
中科院分区：
文献类型：
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作者：
K. Meyer;S. Platnick;L. Oreopoulos;Dongmin Lee
吸收性气溶胶（如烟雾）强烈吸收太阳辐射，特别是紫外线和可见光/近红外（VIS/NIR）波长的辐射，它们在云层上方的存在可能会产生相当大的影响。以前的研究表明，当它们覆盖在明亮的云层上时，它们具有积极的（即变暖的）直接气溶胶辐射效应（DARE）。此外，在依靠VIS/NIR波长推断下垫云的云光学厚度（COT）和有效半径（re）的技术中，它们可能导致有偏差的被动仪器卫星检索，从而产生有偏差的云上DARE估计。本文研究了正交偏振云气溶胶激光雷达（CALIOP）观测到的上覆吸收气溶胶造成的中分辨率成像光谱仪（MODIS）云光学特性检索偏差，并研究了这些偏差对云上DARE估计的影响。调查集中在8月和9月（2006-2011年）东南大西洋的一个地区，非洲南部生物质燃烧产生的烟雾覆盖在持续的海洋边界层层积云上。对云上气溶胶衰减进行调整后，区域平均液体COT（所有仅面向海洋的液体云的平均值）增加了大约6%；平均re增加了大约2.6%，几乎完全是由于在非正交检索空间中的COT调整。研究发现，这两种偏差导致了对DARE的低估。对于CALIOP观测到的云上烟雾的液态云Aqua MODIS像元，当使用偏差校正而不是非校正的MODIS云反演时，观测时间（Aqua高架桥当地中午附近）的区域平均云上辐射强迫效率（单位气溶胶光学深度（AOD）的DARE）从50.9Wm−2AOD−1增加到65.1Wm−2AOD−1。
Absorbing aerosols such as smoke strongly absorb solar radiation, particularly at ultraviolet and visible/near‐infrared (VIS/NIR) wavelengths, and their presence above clouds can have considerable implications. It has been previously shown that they have a positive (i.e., warming) direct aerosol radiative effect (DARE) when overlying bright clouds. Additionally, they can cause biased passive instrument satellite retrievals in techniques that rely on VIS/NIR wavelengths for inferring the cloud optical thickness (COT) and effective radius (re) of underlying clouds, which can in turn yield biased above‐cloud DARE estimates. Here we investigate Moderate Resolution Imaging Spectroradiometer (MODIS) cloud optical property retrieval biases due to overlying absorbing aerosols observed by Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) and examine the impact of these biases on above‐cloud DARE estimates. The investigation focuses on a region in the southeast Atlantic Ocean during August and September (2006–2011), where smoke from biomass burning in southern Africa overlies persistent marine boundary layer stratocumulus clouds. Adjusting for above‐cloud aerosol attenuation yields increases in the regional mean liquid COT (averaged over all ocean‐only liquid clouds) by roughly 6%; mean re increases by roughly 2.6%, almost exclusively due to the COT adjustment in the non‐orthogonal retrieval space. It is found that these two biases lead to an underestimate of DARE. For liquid cloud Aqua MODIS pixels with CALIOP‐observed above‐cloud smoke, the regional mean above‐cloud radiative forcing efficiency (DARE per unit aerosol optical depth (AOD)) at time of observation (near local noon for Aqua overpass) increases from 50.9Wm−2AOD−1 to 65.1Wm−2AOD−1 when using bias‐adjusted instead of nonadjusted MODIS cloud retrievals.