The simulation of volcanic ash transport and deposition (VATD) for distances within a few kilometres from the vent (proximal region) is challenging owing to a combination of unresolved volcanogenic effects and the impact of the volcano's orography. Due to the urgency of calculations or sometimes lack of access to computational resources or expertise, atmospheric vertical velocity (w) is often underestimated in VATD modelling. The error associated with this underestimation has, however, never been properly quantified. Here, we use a weak vulcanian eruption that occurred at Sakurajima volcano on 1/10/2017 as a first step to addressing this limitation. We combine deposit characteristics observed by disdrometer measurements with high-resolution atmospheric and VATD modelling to validate and illustrate the differences in modelled trajectories when w is either ignored or accounted for. The Weather Research and Forecasting (WRF) model is used to model the orogenic effects down to a resolution of 50 m. Eulerian and Lagrangian VATD models (FALL3D and LagTrack, a newly-developed Matlab code, respectively) are used to describe the particle trajectories. Results confirm the importance of w in the case of low-altitude eruptions for capturing the complex, near-vent trajectory of ash particles: when neglected fall velocities were seen to differ up to 2–5 m s⁻¹ depending on the particle size. Although the impact of w is most notable within 10 km from the vent, the forced sedimentation of low terminal velocity particles can have a significant secondary effect at larger distances.

由于尚未解决的火山成因作用和火山地形的影响相结合，因此模拟距火山口（近端区域）几公里内的火山灰迁移和沉积（VATD）的工作具有挑战性。由于计算的紧迫性或有时无法获得计算资源或专业知识，大气垂直速度（w）在VATD建模中经常被低估。但是，从未正确量化与这种低估有关的误差。在这里，我们使用在2017年1月1日在樱岛火山上发生的微弱的火山喷发，作为解决这一局限性的第一步。我们将通过测风仪测量观察到的沉积物特征与高分辨率大气和VATD建模相结合，以验证和说明当忽略或考虑到w时建模轨迹的差异。天气研究和预报（WRF）模型用于对低至50 m分辨率的造山效应进行建模。欧拉和拉格朗日VATD模型（分别为FALL3D和LagTrack，分别是新开发的Matlab代码）用于描述粒子轨迹。结果证实了w在低空喷发以捕获复杂，近乎通风的烟灰颗粒轨迹的情况下：当被忽略的下降速度视颗粒大小而异，最高达2–5 ms ^-1。尽管w的影响在距通风孔10公里以内最为明显，但低终速度粒子的强迫沉降在较大距离处可能会产生明显的次要影响。