Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
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DOI：
10.5194/acp-21-16869-2021
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发表时间：
2021-11-19
影响因子：
6.3
通讯作者：
Kok, Jasper F.
中科院分区：
文献类型：
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作者：
Ito, Akinori;Adebiyi, Adeyemi A.;Kok, Jasper F.
矿物尘埃气溶胶通过散射和吸收太阳（短波：SW）和热（长波：LW）辐射来冷却和温暖大气。然而，尘埃辐射效应仍然存在很大的不确定性，这主要是由于地球系统模型模拟的尘埃尺寸分布和光谱光学特性的差异。粉尘模型通常会低估粗粉尘负荷（直径超过 2.5 μm）并假设为球形，这会导致在模型中的粉尘排放按比例缩放以匹配在 550 nm 处观察到的粉尘气溶胶光学深度 (DAOD(550)) 后，会高估细粉尘负荷（小于 2.5 μm）。在这里，我们利用数据集改进了模拟的灰尘特性，这些数据集利用了具有辐射传输模块的耦合全局化学传输模型中的尺寸分辨灰尘浓度、非球面系数和折射率的测量。调整尺寸分辨灰尘浓度和光谱光学特性后，模拟的 DAOD(550) 全球和年平均值从 0.023 增加到 0.029，落在半观测估计的范围内 (0.030 +/- 0.005)。调整后细尘负荷的减少导致大气顶部SW冷却（TOA）减少。为了提高与 TOA 辐射效应效率半观测估计的一致性，我们发现较粗的非球面尘埃需要较低吸收性的 SW 尘埃折射率。因此，TOA 处的全球尘埃净辐射效应估计仅有微小差异（全球范围内-0.08 与-0.00 W m(-2)）。相反，我们的敏感性模拟表明，强尘源区域附近的地表变暖显着增强（全球范围内从-0.60 W m(-2) 冷却到-0.23 的程度较低）。因此，由于较粗尺寸和非球面形状的协同作用增强了地表的长波变暖，估计主要源区附近的大气辐射加热较少（全球范围内的加热从0.59 W m(-2)减少到0.15）。
Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical properties simulated in Earth system models. Dust models typically underestimate the coarse dust load (more than 2.5 mu m in diameter) and assume a spherical shape, which leads to an overestimate of the fine dust load (less than 2.5 mu m) after the dust emissions in the models are scaled to match observed dust aerosol optical depth at 550 nm (DAOD(550)). Here, we improve the simulated dust properties with data sets that leverage measurements of size-resolved dust concentration, asphericity factor, and refractive index in a coupled global chemical transport model with a radiative transfer module. After the adjustment of size-resolved dust concentration and spectral optical properties, the global and annual average of DAOD(550) from the simulation increases from 0.023 to 0.029 and falls within the range of a semi-observationally based estimate (0.030 +/- 0.005). The reduction of fine dust load after the adjustment leads to a reduction of the SW cooling at the top of the atmosphere (TOA). To improve agreement against a semi-observationally based estimate of the radiative effect efficiency at TOA, we find that a less absorptive SW dust refractive index is required for coarser aspherical dust. Thus, only a minor difference is estimated for the net global dust radiative effect at TOA (-0.08 vs. -0.00 W m(-2) on a global scale). Conversely, our sensitivity simulations reveal that the surface warming is substantially enhanced near the strong dust source regions (less cooling to -0.23 from -0.60 W m(-2) on a global scale). Thus, less atmospheric radiative heating is estimated near the major source regions (less heating to 0.15 from 0.59 W m(-2) on a global scale), because of enhanced LW warming at the surface by the synergy of coarser size and aspherical shape.