Saharan dust and biomass burning aerosols during ex-hurricane Ophelia: observations from the new UK lidar and sun-photometer network
Saharan dust and biomass burning aerosols during ex-hurricane Ophelia: observations from the new UK lidar and sun-photometer network
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DOI：
10.5194/acp-19-3557-2019
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发表时间：
2019-03
影响因子：
6.3
通讯作者：
Martin Osborne;F. Malavelle;M. Adam;J. Buxmann;J. Sugier;F. Marenco;J. Haywood
中科院分区：
文献类型：
--
作者：
Martin Osborne;F. Malavelle;M. Adam;J. Buxmann;J. Sugier;F. Marenco;J. Haywood
抽象的。2017年10月15日至16日，前飓风奥菲莉亚经过不列颠群岛以西，带来了来自撒哈拉沙漠的沙尘和葡萄牙森林大火的烟雾，这是肉眼可以观察到的，并在英国全国媒体上进行了报道。我们在这里报告了使用英国运行的激光雷达和太阳光度计网络对这一事件进行的详细观测，该网络是为早期检测航空危险而建立的，包括火山灰。我们还利用ECMWF ERA5风场资料和MODIS图像研究了气溶胶输送。连续30小时的观测显示了一幅复杂的图像，在不同的时间由几个不同的气溶胶层主导，并与与强气旋系统相关的不同气团的通过明显相关。在几个地点也观察到了类似的演变，它们之间的时间延迟是由于它们相对于风暴的不同位置和相关的气象特征。这次事件开始于海拔1-2公里的浅沙尘层，最终形成了一个深而复杂的结构，在英国上空的每个地点持续了12小时，与风暴的温暖部分相关。在大多数时间里，探测到的气溶胶主要是矿物尘埃混合物，去极化测量突出了这一点，但在事件结束时观察到了一个强烈的生物质燃烧气溶胶(BBA)层，在每个地点持续约3小时。整个过程中355 nm处的气溶胶光学厚度(AOD355)在0.2~2.9之间变化，较大的AOD值与较强的BBA层相关。根据AERONET过去20年的记录，如此大的AOD在英国是前所未有的。拉曼激光雷达可以测量355 nm处的气溶胶消光系数、粒子线消偏率(PLDR)和激光雷达比(LR)，并使尘埃(去极化)气溶胶与其他类型的气溶胶分离成为可能。还计算了特定消光系数，以分别估计这两种气溶胶的大气浓度，粉尘的最高浓度为420±200微克m−3，生物质燃烧气溶胶的最高浓度为558±232微克m−3。使用数值大气扩散模拟环境(NAME)计算的后向轨迹被用来确定来源并加强从观测中得出的结论。英国的网络代表着北欧观测能力的显著扩展，仪器均匀分布在从康沃尔的坎伯恩到设得兰群岛的勒威克的大不列颠各地，这项研究是证明其能力和验证使用的方法的首次尝试。其最终目的将是探测和量化火山羽流，但本研究清楚地表明了该网络的先进能力。
Abstract. On 15–16 October 2017, ex-hurricane Ophelia passed to the west of the British Isles, bringing dust from the Sahara and smoke from Portuguese forest fires that was observable to the naked eye and reported in the UK's national press. We report here detailed observations of this event using the UK operational lidar and sun-photometer network, established for the early detection of aviation hazards, including volcanic ash. We also use ECMWF ERA5 wind field data and MODIS imagery to examine the aerosol transport. The observations, taken continuously over a period of 30 h, show a complex picture, dominated by several different aerosol layers at different times and clearly correlated with the passage of different air masses associated with the intense cyclonic system. A similar evolution was observed at several sites, with a time delay between them explained by their different location with respect to the storm and associated meteorological features. The event commenced with a shallow dust layer at 1–2 km in altitude and culminated in a deep and complex structure that lasted ∼12 h at each site over the UK, correlated with the storm's warm sector. For most of the time, the aerosol detected was dominated by mineral dust mixtures, as highlighted by depolarisation measurements, but an intense biomass burning aerosol (BBA) layer was observed towards the end of the event, lasting around 3 h at each site. The aerosol optical depth at 355 nm (AOD355) during the whole event ranged from 0.2 to 2.9, with the larger AOD correlated to the intense BBA layer. Such a large AOD is unprecedented in the UK according to AERONET records for the last 20 years. The Raman lidars permitted the measurement of the aerosol extinction coefficient at 355 nm, the particle linear depolarisation ratio (PLDR), and the lidar ratio (LR) and made the separation of the dust (depolarising) aerosol from other aerosol types possible. A specific extinction has also been computed to provide an estimate of the atmospheric concentration of both aerosol types separately, which peaked at 420±200 µg m−3 for the dust and 558±232 µg m−3 for the biomass burning aerosols. Back trajectories computed using the Numerical Atmospheric-dispersion Modelling Environment (NAME) were used to identify the sources and strengthen the conclusions drawn from the observations. The UK network represents a significant expansion of the observing capability in northern Europe, with instruments evenly distributed across Great Britain, from Camborne in Cornwall to Lerwick in the Shetland Islands, and this study represents the first attempt to demonstrate its capability and validate the methods in use. Its ultimate purpose will be the detection and quantification of volcanic plumes, but the present study clearly demonstrates the advanced capabilities of the network.