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Taking the pulse of pyrocumulus clouds

机译:以焦积云的脉动

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摘要

Large forest fires are a known natural and dominant disturbance factor in high northern latitudes, and form pyrocumulus (pyroCu), and occasionally pyrocumulonimbus (pyroCb) clouds. These clouds can transport emissions into the upper troposphere/lower stratosphere (UT/LS) and produce significant regional and even global climate effects, as is the case with some volcanoes. However, the lack of observational data within pyroCu or pyroCb complicates our ability to investigate pyro-convection and to understand the vertical and cross-isentropic transport mechanisms responsible for UT/LS injection. Here, we report detailed airborne radiation measurements within strong pyroCu taken over boreal forest fires in Saskatchewan, Canada during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) summer field campaign in 2008. We find a prominent smoke core within the pyroCu, which is defined by strong extinction in the UV, VIS and NIR, and high gas-particle concentrations. We also find that the angular distribution of radiance within the pyroCu is closely related to the diffusion domain in water clouds, which is dominated by multiple scattering processes. The radiation field of pyroCu can be described by diffusion approximations that are comprised of simple cosine functions, which can be used to calculate the spatial and temporal characteristics of the radiance field, and applied in cloud resolving models. We demonstrate with Monte Carlo simulations that radiation transport in pyroCu is inherently a 3D problem and must account for particle absorption.
机译:森林大火是北部高纬度地区已知的自然和主要干扰因素,会形成焦积云(pyroCu),并偶尔形成焦积云(pyroCb)云。这些云可以将排放物输送到对流层高空/平流层低层(UT / LS),并产生重要的区域乃至全球气候影响,就像某些火山一样。但是,焦磷酸铜或焦磷酸Cb缺乏观测数据,使我们研究热对流以及了解负责UT / LS注入的垂直和等熵输运机制的能力复杂化。在这里,我们报告了在加拿大萨斯喀彻温省北部森林大火期间进行的强焦火气中的详细空中传播辐射测量,该研究是在2008年飞机和卫星对流层组成的北极研究(ARCTAS)夏季野外活动期间进行的。 pyroCu,其定义是在UV,VIS和NIR中强烈消光,以及高的气体颗粒浓度。我们还发现,pyroCu内辐射度的角分布与水云中的扩散域密切相关,后者由多个散射过程控制。可以通过由简单余弦函数组成的扩散近似来描述pyroCu的辐射场,该余弦函数可用于计算辐射场的时空特性,并应用于云解析模型中。我们用蒙特卡洛模拟证明,pyroCu中的辐射传输本质上是3D问题,必须考虑颗粒吸收。

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