Abstract. The Hunga volcano violently erupted on January 15th, 2022, and produced the largest stratospheric aerosol layer perturbation of the last 30 years. One notable effect of the Hunga eruption was the significant modification of the size distribution (SD) of the stratospheric aerosol layer with respect to background conditions and other recent moderate stratospheric eruptions, with larger mean particles size and smaller SD spread for Hunga. Starting from satellite-based SD retrievals, and the assumption of pure sulphate aerosol layers, in this work we calculate the optical properties of both background and Hunga-perturbed stratospheric aerosol scenarios using a Mie code. We found that the intensive optical properties of the stratospheric aerosol layer (i.e., single scattering albedo, asymmetry parameter, aerosol extinction per unit mass and the broad-band average Ångström exponent) were not significantly perturbed by the Hunga eruption, with respect to background conditions. The calculated Ångström exponent was found consistent with multi-instrument satellite observations of the same parameter. Thus, the basic impact of the Hunga eruption on the optical properties of the stratospheric aerosol layer was an increase of the stratospheric aerosol extinction (or optical depth), without any modification of the shortwave and longwave relative absorption, angular scattering and broad-band spectral trend of the extinction, with respect to background. This highlights a marked difference of the Hunga perturbation of the stratospheric aerosol layer and those from other larger stratospheric eruptions, like Pinatubo 1991 and El Chichon 1982. With simplified radiative forcing estimations, we show that the Hunga eruption produced an aerosol layer likely 3–10 times more effective in producing a net cooling of the climate system with respect to Pinatubo and El Chichon eruptions, due to more effective shortwave scattering. As intensive optical properties are seldom directly measured, e.g. from satellite, our calculations can support the estimation of radiative effects for the Hunga eruption with climate or offline radiative models.

中文翻译：

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2022年1月15日洪加火山喷发平流层气溶胶层扰动的光学特性


摘要。洪加火山于2022年1月15日猛烈喷发，产生了近30年来最大的平流层气溶胶层扰动。洪加喷发的一个显着影响是平流层气溶胶层的尺寸分布（SD）相对于背景条件和最近其他中度平流层喷发的显着改变，洪加喷发的平均颗粒尺寸更大，SD分布更小。从基于卫星的 SD 反演和纯硫酸盐气溶胶层的假设开始，在这项工作中，我们使用 Mie 代码计算背景平流层气溶胶场景和平流层气溶胶场景的光学特性。我们发现，相对于背景条件，平流层气溶胶层的强光学特性（即单次散射反照率、不对称参数、单位质量气溶胶消光和宽带平均 Ångström 指数）并未受到洪加喷发的显着干扰。计算出的 Ångström 指数与相同参数的多仪器卫星观测结果一致。因此，洪加喷发对平流层气溶胶层光学特性的基本影响是平流层气溶胶消光（或光学深度）的增加，而对短波和长波相对吸收、角散射和宽带光谱没有任何改变。相对于背景而言，灭绝的趋势。这凸显了平流层气溶胶层的洪加扰动与其他较大平流层喷发（例如 1991 年的皮纳图博火山和 1982 年的埃尔奇琼火山）的显着差异。 通过简化的辐射强迫估计，我们表明，由于更有效的短波散射，洪加火山喷发产生的气溶胶层在产生气候系统净冷却方面的效率可能是皮纳图博火山和埃尔奇琼火山喷发的3-10倍。由于密集的光学特性很少直接测量，例如通过卫星，我们的计算可以支持利用气候或离线辐射模型来估计洪加火山喷发的辐射效应。