Refining an ensemble of volcanic ash forecasts using satellite retrievals: Raikoke 2019
Refining an ensemble of volcanic ash forecasts using satellite retrievals: Raikoke 2019
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DOI：
10.5194/acp-2021-858
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发表时间：
2021-11
影响因子：
6.3
通讯作者：
A. Capponi;N. Harvey;H. Dacre;K. Beven;C. Saint;Cathie A. Wells;M. James
中科院分区：
文献类型：
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作者：
A. Capponi;N. Harvey;H. Dacre;K. Beven;C. Saint;Cathie A. Wells;M. James
抽象的。火山灰咨询由专业预报员制作，他们根据自己的主观专业知识，结合多种观测数据来源和火山灰扩散模型输出。航空业利用这些建议来决定安全飞行的地点。然而，观测和离散模型模拟都受到业务预测中未体现的各种不确定性来源的影响。这些不确定性的量化和沟通对于做出更明智的决策至关重要。在这里，我们开发了一种数据同化技术，结合了卫星检索和火山灰输送和扩散模型（VATDM）输出，并考虑了两个数据源的不确定性。该方法应用于 2019 年 Raikoke 喷发的案例研究。为了表示 VATDM 输出的不确定性，通过同时扰动喷发源参数、气象和内部模型参数（称为先验系综）来执行 1000 次模拟。根据与 Himawari 卫星检索的灰柱载荷的一致程度，对集合成员进行过滤，以产生受卫星数据及其不确定性约束的后验集合。对于 Raikoke 喷发，过滤系综会将质量喷发率的值偏向先前系综中最初使用的更宽参数范围内的较低值（平均值从 1 Tg h−1 减少到 0.1 Tg h−1）。此外，包括随后时代的卫星观测越来越多地限制了后验集合。这些结果表明，先前的集合导致了对灰柱载荷的大小和不确定性的高估。根据之前的总体情况，太平洋上空的飞行运营将受到严重干扰。使用受约束的后验集合，可以减少风险被高估的区域，从而可能减少航班中断。本文开发的数据同化方法很容易推广到其他短期喷发和其他 VATDM 以及从其他卫星检索火山灰。
Abstract. Volcanic ash advisories are produced by specialised forecasters who combine several sources of observational data and volcanic ash dispersion model outputs based on their subjective expertise. These advisories are used by the aviation industry to make decisions about where it is safe to fly. However, both observations and dispersion model simulations are subject to various sources of uncertainties that are not represented in operational forecasts. Quantification and communication of these uncertainties are fundamental for making more informed decisions. Here, we develop a data assimilation technique which combines satellite retrievals and volcanic ash transport and dispersion model (VATDM) output, considering uncertainties in both data sources. The methodology is applied to a case study of the 2019 Raikoke eruption. To represent uncertainty in the VATDM output, 1000 simulations are performed by simultaneously perturbing the eruption source parameters, meteorology and internal model parameters (known as the prior ensemble). The ensemble members are filtered, based on their level of agreement with Himawari satellite retrievals of ash column loading, to produce a posterior ensemble that is constrained by the satellite data and its uncertainty. For the Raikoke eruption, filtering the ensemble skews the values of mass eruption rate towards the lower values within the wider parameters ranges initially used in the prior ensemble (mean reduces from 1 Tg h−1 to 0.1 Tg h−1). Furthermore, including satellite observations from subsequent times increasingly constrains the posterior ensemble. These results suggest that the prior ensemble leads to an overestimate of both the magnitude and uncertainty in ash column loadings. Based on the prior ensemble, flight operations would have been severely disrupted over the Pacific Ocean. Using the constrained posterior ensemble, the regions where the risk is overestimated are reduced potentially resulting in fewer flight disruptions. The data assimilation methodology developed in this paper is easily generalisable to other short duration eruptions and to other VATDMs and retrievals of ash from other satellites.