Abstract. In order to improve aerosol representation in the NASA Goddard Earth Observing System (GEOS) model, we evaluated simulations of the transport and properties of aerosols from southern African biomass burning sources that were observed during the first deployment of the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) field campaign in September 2016. An example case study of 24 September was analyzed in detail, during which aircraft-based in situ and remote sensing observations showed the presence of a multi-layered smoke plume structure with significant vertical variation in single scattering albedo (SSA). Our baseline GEOS simulations were not able to represent the observed SSA variation or the observed organic aerosol-to-black-carbon ratio (OA : BC). Analyzing the simulated smoke age suggests that the higher-altitude, less absorbing smoke plume was younger (∼4 d), while the lower-altitude and more absorbing smoke plume was older (∼7 d). We hypothesize a chemical or microphysical loss process exists to explain the change in aerosol absorption as the smoke plume ages, and we apply a simple loss rate to the model hydrophilic biomass burning OA to simulate this process. We also utilized the ORACLES airborne observations to better constrain the simulation of aerosol optical properties, adjusting the assumed particle size, hygroscopic growth, and absorption. Our final GEOS model simulation with additional OA loss and updated optics showed better performance in simulating aerosol optical depth (AOD) and SSA compared to independent ground- and space-based retrievals for the entire month of September 2016, including the Ozone Monitoring Instrument (OMI) Aerosol Index. In terms of radiative implications of our model adjustments, the final GEOS simulation suggested a decreased atmospheric warming of about 10 % (∼2 W m−2) over the southeastern Atlantic region and above the stratocumulus cloud decks compared to the model baseline simulations. These results improve the representation of the smoke age, transport, and optical properties in Earth system models.

中文翻译：

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在 ORACLES-I 活动期间，改进了 NASA GEOS 模型中生物质燃烧气溶胶光学特性和寿命的模拟

摘要。为了改善 NASA 戈达德地球观测系统 (GEOS) 模型中的气溶胶表征，我们评估了对来自南部非洲生物质燃烧源的气溶胶的传输和特性的模拟，这些气溶胶是在 NASA ORACLES 首次部署期间观察到的（上面的气溶胶观察结果） 2016 年 9 月的云及其相互作用）现场活动。详细分析了 9 月 24 日的案例研究，在此期间基于飞机的现场和遥感观测显示，存在多层烟羽结构，且垂直变化显着单散射反照率（SSA）。我们的基线 GEOS 模拟无法代表观察到的 SSA 变化或观察到的有机气溶胶与黑碳的比率（OA：BC）。分析模拟烟龄表明，海拔较高、吸收较少的烟羽较年轻（∼4 d），而海拔较低、吸收较多的烟羽较老（∼7 d）。我们假设存在化学或微观物理损失过程来解释烟羽老化时气溶胶吸收的变化，并且我们将简单的损失率应用于亲水生物质燃烧 OA 模型来模拟该过程。我们还利用 ORACLES 机载观测来更好地约束气溶胶光学特性的模拟，调整假设的粒径、吸湿性增长和吸收。与 2016 年 9 月整个月的独立地基和空基检索（包括臭氧监测仪器（OMI） ) 气溶胶指数。就我们模型调整的辐射影响而言，最终的 GEOS 模拟表明，与模型基线模拟相比，东南大西洋地区和层积云层上方的大气变暖减少了约 10% (∼2 W m−2)。这些结果改进了地球系统模型中烟龄、传输和光学特性的表示。