SAFARI 2000 C-130 AEROSOL AND METEOROLOGICAL DATA, DRY SEASON 2000

The Met Office C-130 research aircraft was based at Windhoek, Namibia between September 5-16, 2000, where it conducted a series of flights over Namibia as part of the SAFARI 2000 Dry Season Aircraft Campaign.The effects of atmospheric aerosols on the Earth's radiation balance are known to be very important, but for many types of aerosols these effects are still poorly understood. In particular, aerosol particles produced from biomass burning (associated with Savanna burning, domestic fuel wood consumption, and certain agricultural practices) are thought to be particularly important because they can both absorb and scatter solar radiation. Understanding the correct balance between absorption and scattering is fundamental to the accurate calculation of aerosol effects on local and global climate.The atmosphere of southern Africa is experiencing significant changes at present, due to the emission of trace gases and aerosols from three distinct sources: the burning of fossil fuels and other industrial activities; biomass burning; and natural processes in the terrestrial and aquatic ecosystems of the regions. Specifically, the burning of fossil fuels in mining, industrial and domestic activities are in part responsible for rising levels of atmospheric aerosols and trace gases (Held et al., 1996), and these emissions, augmented by those from extensive biomass burning areas (Crutzen and Andreae, 1990) and from biogenic sources (Harris et al., 1996), may be altering the biogeochemical cycling of essential nutrients in the region (Garstang et al., 1998).For these reasons, it is important to quantify the relative contributions from the different types of emissions, understand their transport and transformations in the atmosphere, and to determine their influence on regional climate and weather, together with knowledge of the deposition processes and the effects of this deposition on the local ecosystems. SAFARI 2000 was developed as part of an international programme aimed at developing a better understanding of the southern African earth-atmosphere-human system. The aims of the Met Office's research were:1. In-situ measurements of the physical, chemical and optical properties of the aerosol. Size distributions to be measured using PCASP, FSSP and CVI instrumentation. Chemical composition inferred from filter measurements. Optical properties from PSAP and nephelometer data. The data set includes aerosol samples ranging from near source regions to aged plumes several hundreds of kilometres from source, some of which have been cloud processed.2. Investigate the direct radiative impact of aerosol over sea, land and low-level cloud. High-altitude radiation measurements taken from SAFIRE, ARIES, SWS and the broad-band radiometers will be used to infer the direct radiative impact of the aerosol. Low-level orbits and into- and down-sun runs will be used in an attempt to obtain radiative closure. Over land, the ground-based sun photometers may also prove useful for constraining the data.3. In-situ measurements of aerosol properties in conjunction with ground-based sites, in order to validate the ground-based retrievals of, for example, aerosol size distributions.4. In-situ measurements of aerosol properties in conjunction with TERRA overpasses, in order to validate the satellite-based retrievals of aerosol properties.5. In-situ measurements of stratus/stratocumulus cloud of Namibia/Angola in conjunction with TERRA overpasses, in order to validate satellite-based retrievals of cloud properties.

英国气象局（Met Office）的C-130科研飞机于2000年9月5日至16日以纳米比亚温得和克为基地，作为SAFARI 2000旱季航空科考计划的一部分，在纳米比亚上空开展了一系列飞行任务。
大气气溶胶对地球辐射平衡的影响至关重要，但目前对多数类型气溶胶的相关气候效应仍缺乏充分认知。其中，由生物质燃烧（涉及稀树草原焚烧、民用薪柴消耗及特定农业活动）产生的气溶胶颗粒，因其兼具太阳辐射吸收与散射能力，被认为具有尤为显著的气候影响。厘清吸收与散射间的精确平衡，是准确计算气溶胶对局地及全球气候影响的核心前提。
当前南部非洲大气正经历显著变化，其诱因来自三类截然不同的排放源所释放的痕量气体与气溶胶：化石燃料燃烧及其他工业活动、生物质燃烧，以及该区域陆地与水生生态系统的自然过程。具体而言，采矿、工业及民用活动中的化石燃料燃烧是大气气溶胶与痕量气体浓度上升的部分成因（Held et al., 1996）；此类排放叠加大规模生物质燃烧区域的排放（Crutzen and Andreae, 1990）与生物源排放（Harris et al., 1996），可能正在改变该区域关键营养物质的生物地球化学循环（Garstang et al., 1998）。
基于上述原因，量化不同排放类型的相对贡献、厘清其在大气中的传输与转化过程、明确其对局地气候与天气的影响，同时掌握气溶胶沉降过程及其对当地生态系统的效应，均具有重要科学意义。SAFARI 2000作为一项国际研究计划的组成部分，旨在加深对南部非洲地球-大气-人类系统的理解。英国气象局此次科研的目标如下：
1. 开展气溶胶物理、化学与光学特性的原位（in-situ）测量：使用PCASP、FSSP与CVI仪器测定气溶胶粒径分布；通过滤膜采样测量推断其化学组成；基于PSAP与浊度计（nephelometer）数据获取其光学特性。本数据集涵盖从近源区域至距排放源数百公里的老化羽流的气溶胶样本，其中部分样本曾经过云过程处理。
2. 研究气溶胶在海洋、陆地与低云上空的直接辐射效应。将利用SAFIRE、ARIES、SWS与宽带辐射计获取的高空辐射测量数据，推断气溶胶的直接辐射影响；通过低空轨道飞行以及顺光、逆光航线，尝试实现辐射闭合。在陆地区域，地基太阳光度计或也可用于约束数据集的精度。
3. 结合地基观测站点开展气溶胶特性原位测量，以验证气溶胶粒径分布等地基反演结果。
4. 结合泰拉卫星（TERRA）过境时段开展气溶胶特性原位测量，以验证基于卫星的气溶胶特性反演结果。
5. 结合泰拉卫星（TERRA）过境时段，对纳米比亚/安哥拉上空的层云/层积云开展原位测量，以验证基于卫星的云特性反演结果。