This paper demonstrates the advantages of three-dimensional (3D) analysis and visualization of weather radar data for studies on the inner structure of eruption columns and their 3D ash-fall distributions. The 3D data were collected using an operational X-band polarimetric radar located ~11 km from the Showa vent of Sakurajima, Japan. Three eruption cases were chosen for the analysis to study the effect of environmental wind conditions on the inner structure of an eruption column and horizontal ash-fall distributions at 1000 m height: a 3677-m-high eruption on 13 June 2013 under calm winds (Case 1), a 3982-m-high eruption on 7 October 2013 under strong winds (Case 2), and a 4520-m-high eruption on 18 August 2013 under moderate winds (Case 3). The Analytical Tools for Three-dimensional Weather Radar Data (ANT3D) package was developed and used for the construction of 3D constant altitude plan position indicator (3D CAPPI) data from eruption columns. The quantitative ash-fall analyses of 3D CAPPI data revealed that the total ash-fall amounts of the Case 1, Case 2, and Case 3 eruptions were 6.24 × 10⁷, 9.99 × 10⁷, and 6.71 × 10⁷ kg, respectively, and the total ash-fall areas at the 1000-m height were 29.7, 151.3, and 107.7 km², respectively. It was shown that the area of the maximum ash-fall amount at the 1000-m height depends on the environmental conditions. The accumulated ash-fall distribution area was limited to over and around the vent in the Case 1 eruption, whereas the ash distribution pattern was elongated to the downwind direction and multiple ash concentration maxima were formed in the Case 2 eruption probably due to the multiple eruptions. The accumulated ash-fall distribution was also elongated to the down wind direction in the Case 3 eruption but a single maximum concentration which was larger than that in the Case 2 eruption was found inland of Sakurajima. The 3D CAPPI data were visualized using techniques such as surface rendering, volume rendering, bird's eye viewing, and cross-sectional analysis. The 3D visualizations suggest that vertical size-sorting and aggregation occurred in the buoyancy-driven regions of the eruption columns in all three cases. The results of this study will contribute to the understanding of volcanic eruption column dynamics and horizontal ash-fall transportation.

本文展示了三维（3D）分析和天气雷达数据可视化在研究喷发柱的内部结构及其3D灰分分布方面的优势。3D数据是使用可操作的X波段极化雷达收集的，该雷达位于距日本樱岛昭和喷口约11公里处。选择了三个喷发案例进行分析，以研究环境风条件对喷发柱内部结构和高度1000 m处的水平灰分分布的影响：2013年6月13日在平静风下喷发高3677 m（案例1），2013年10月7日在强风下喷发高3982米（案例2），2013年8月18日在中等风向喷发高4520 m（案例3）。开发了三维天气雷达数据分析工具（ANT3D）软件包，并将其用于从喷发列构建3D恒定高度计划位置指示器（3D CAPPI）数据。对3D CAPPI数据进行的灰分定量分析显示，案例1，案例2和案例3喷发的总降灰量为6.24×10⁷，9.99×10 ⁷，和6.71×10 ⁷ 公斤，分别与在1000米的高度的总落灰区分别为29.7，151.3，和107.7公里²， 分别。结果表明，最大灰烬沉降量在1000米高度处的面积取决于环境条件。在案例1的爆发中，累积的灰分分布区域仅限于通风口上方和周围，而在案例2的爆发中，灰分分布模式向顺风方向拉长，并且形成了多个灰分浓度最大值，这可能是由于多次爆发造成的。案例3爆发时，累积的灰分分布也沿顺风方向拉长，但在樱岛内陆发现了一个最大浓度大于案例2爆发的最大浓度。使用诸如表面绘制，体积绘制，鸟瞰图和横截面分析之类的技术可视化3D CAPPI数据。3D可视化结果表明，在所有三种情况下，垂直大小的排序和聚集都在喷发列的浮力驱动区域中发生。这项研究的结果将有助于理解火山喷发柱动力学和水平灰分沉降运移。