Abstract. A simulation study on the impact of wildfire smoke (aged organic aerosol particles) on cirrus formation in the central Arctic is presented. The simulations in this part 2 of a series of two articles complement the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) field observations, presented and discussed in part 1. The measurements were performed with lidar and radar aboard the ice breaker Polarstern at latitudes > 85° N during the winter half year 2019–2020. Main goal of the MOSAiC data analysis in part 1 was to gather a consistent set of indications for an impact of the observed aged Siberian wildfire smoke on the formation of embedded ice clouds. The combination of (a) mostly low ice crystal number concentration (ICNC) of 0.1–10 L⁻¹ in almost all of the observed cirrus cloud virga, pointing to heterogeneous ice nucleation, (b) typically high ice saturation ratios in the upper part of the analyzed cirrus systems of around 1.3–1.4, and (c) significantly enhanced levels of smoke pollution characterized by particle surface area concentrations of the order of 5–15 µm² cm⁻³ corroborate our hypothesis that wildfire smoke particles served as ice nucleating particles (INPs) in Arctic cirrus with typical cloud top temperatures of −60 to −75 °C. The observed high ice saturation ratios suggest relatively inefficient ice-active aerosol particles, as expected in the case of wildfire smoke. Main goal of the simulations in part 2 is to gain a deeper insight into the potential smoke influence on cirrus formation as a function of aerosol and meteorological conditions (temperature, relative humidity) and by considering realistic gravity wave characteristics (updraft speed, wave amplitude). The modeling effort uses lidar-derived values of INP number concentration as input and ICNC values retrieved from combined lidar-radar observations for comparison with the simulation results. The model allows us to simulate adiabatic lofting of air parcels triggered by gravity waves, nucleation of ice crystals on smoke particles (deposition ice nucleation), homogeneous freezing of background aerosol particles, the growth of the nucleated ice particles by deposition of water vapor on the crystals, and sedimentation effects. Observations of meteorological state parameters (temperature, relative humidity) with four radiosondes per day and of the aerosol and cirrus properties from continuous lidar and radar profiling permitted a realistic model-based investigation of the smoke influence on Arctic cirrus evolution. The simulations confirm that the smoke INPs were able to suppress homogeneous freezing of background aerosol particles and to trigger ice nucleation at high ice saturation ratios of 1.3–1.5 over the North Pole region at cirrus top temperatures mostly < −60 °C. The simulations further reveal that shallow gravity waves with amplitudes of the order of < 100 m and the comparably low ice nucleation efficiency of the smoke INPs provided favorable conditions for the evolution of thin ice clouds with low ICNC as observed.

中文翻译：

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野火烟雾对北极卷云形成的影响，第 2 部分：MOSAiC 2019−2020 年案例模拟


摘要。提出了关于野火烟雾（老化有机气溶胶颗粒）对北极中部卷云形成影响的模拟研究。两篇文章系列的第二部分中的模拟补充了第 1 部分中介绍和讨论的 MOSAiC（北极气候研究多学科漂流观测站）实地观测。测量是在破冰船 Polarstern 上使用激光雷达和雷达进行的。 2019-2020 年冬半年纬度 > 85° N。第 1 部分 MOSAiC 数据分析的主要目标是收集一组一致的迹象，了解观察到的老化西伯利亚野火烟雾对嵌入式冰云形成的影响。 (a) 几乎所有观测到的卷云 virga 中冰晶数浓度 (ICNC) 大多较低，为 0.1–10 L ⁻¹ ，表明冰核不均匀；(b) 通常较高的冰饱和度所分析的卷云系统上部的比率约为 1.3–1.4，并且 (c) 烟雾污染水平显着增强，其特征是颗粒表面积浓度达到 5–15 µm ² cm ⁻³ 证实了我们的假设，即野火烟雾颗粒在北极卷云中充当冰成核颗粒（INP），典型云顶温度为 -60 至 -75 °C。观察到的高冰饱和比表明冰活性气溶胶颗粒的效率相对较低，正如野火烟雾情况所预期的那样。第 2 部分中模拟的主要目标是更深入地了解烟雾对卷云形成的潜在影响，作为气溶胶和气象条件（温度、相对湿度）的函数，并考虑现实的重力波特征（上升气流速度、波幅） 。 建模工作使用激光雷达导出的 INP 数量浓度值作为输入，并使用从激光雷达-雷达组合观测中检索的 ICNC 值来与模拟结果进行比较。该模型允许我们模拟由重力波触发的气团的绝热放样、烟雾颗粒上冰晶的成核（沉积冰成核）、背景气溶胶颗粒的均匀冻结、通过水蒸气沉积在烟雾颗粒上而形成的成核冰颗粒的生长。晶体和沉淀效应。每天使用四台无线电探空仪观测气象状态参数（温度、相对湿度），并通过连续激光雷达和雷达剖面观测气溶胶和卷云特性，从而可以对烟雾对北极卷云演化的影响进行基于模型的真实调查。模拟证实，烟雾 INP 能够抑制背景气溶胶颗粒的均匀冻结，并在北极地区卷云顶部温度大多 < -60 °C 的高冰饱和比 1.3-1.5 下触发冰成核。模拟进一步表明，振幅<100 m量级的浅层重力波和烟雾INP相对较低的冰成核效率为观察到的低ICNC薄冰云的演化提供了有利条件。