Estimation of emission mass from an eruption plume for the Aso volcano eruption, on October 8, 2016, using a four-dimensional variational method
Estimation of emission mass from an eruption plume for the Aso volcano eruption, on October 8, 2016, using a four-dimensional variational method
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DOI：
10.1186/s40623-018-0964-8
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发表时间：
2018-12-19
影响因子：
3
通讯作者：
Ishii, Kensuke
中科院分区：
文献类型：
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作者：
Ishii, Kensuke
当爆发性喷发，如普林尼式喷发发生时，为了估计火山周围的火山灰下落和减轻灾害，经常使用数值模型。数值模式模拟需要火山喷发柱的喷发质量，包括火山灰颗粒的垂直分布和粒度分布。因此，喷发柱排放质量的准确性对于准确估计和预测火山灰沉降至关重要。我们开发了一个数据同化系统的基础上的四维变分法（4D-Var）的火山喷发柱作为海拔和灰颗粒大小的函数的排放质量的估计方法。该系统包括一个计算火山灰预测的正演模型和一个用于计算观测值与预测值之间失配的观测算子。它还包括一个伴随模型的前向模型，计算校正的排放质量的失配，和一个算法，以最大限度地减少成本函数作为优化的测量。在这个系统中，观测和先验知识的火山喷发柱的排放质量，如铃木函数，可以同时处理的权重，考虑到观测误差和背景误差。此外，该系统具有可扩展性的额外的意见。也就是说，只有当它们的观测算子是从模型参数到观测值的变换时，才能同时处理各种观测。在本研究中，我们将该系统应用于2016年10月8日日本的阿索火山喷发。此次喷发后，在阿索火山周围进行了火山灰落（包括火山灰）观测，业务气象雷达捕捉到了喷发云回波。使用这两个观测和4D-Var系统，我们估计从喷发羽柱作为海拔和颗粒大小的函数的排放质量，它导致了灰落模拟，这是与观测一致。此外，还估算了火山喷发柱的喷发质量为1.32 × 10（8）kg。
When an explosive eruption, such as a Plinian eruption, occurs, in order to estimate ash fall around the volcano and for hazard mitigation, a numerical model is often used. Simulation by a numerical model needs emission mass from the eruption column including vertical profile and size distribution of ash particles. Hence, the accuracy of the emission mass from the eruption column is vital to estimate and forecast ash fall accurately. We developed a data assimilation system based on the four-dimensional variational method (4D-Var) as an estimation method for emission mass from volcanic eruption columns as a function of altitude and ash particle size. This system includes a forward model which calculates volcanic ash forecast, and an observation operator, which are used for the calculation of misfit between observation and forecast. It also includes an adjoint model of the forward model which calculates the correction of emission mass from the misfit, and an algorithm to minimize the cost function as a measurement of optimization. In this system, observation and prior knowledge about emission mass from the volcanic eruption column, such as the Suzuki function, can be simultaneously treated with weight considering observation error and background error. Furthermore, this system has scalability for additional observations. That is to say, a variety of observations can be treated simultaneously, only if their observation operators which are an transformation from model parameters to observation value are developed. In this study, we applied this system to the October 8, 2016 Aso volcano eruption in Japan. After this eruption, ash fall observation (including lapilli) around Aso volcano was preformed, and operational weather radar captured the eruption cloud echo. Using both of these observations and the 4D-Var system, we estimated emission mass from the eruption plume column as a function of altitude and particle size, and it led to ash fall simulation which was consistent with observations. In addition, the eruption mass which is the sum of emission mass from eruption column was estimated to be 1.32x10(8)kg.