Dynamics of Strombolian ash plumes from thermal video: Motion, morphology, and air entrainment
Dynamics of Strombolian ash plumes from thermal video: Motion, morphology, and air entrainment
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热视频中斯特龙博利火山灰羽流的动力学：运动、形态和空气夹带
DOI：
10.1029/2006jb004387
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发表时间：
2007
影响因子：
--
通讯作者：
M. Patrick
中科院分区：
文献类型：
--
作者：
M. Patrick
[1]对火山羽流进行成像对于为了解和模拟羽流动力学提供观测基础至关重要。2004年6月至7月期间，在意大利的斯特龙博利火山，用前视红外辐射计（FLIR）热摄像机（30 Hz）拍摄了150个斯特龙博利火山灰羽流。其中，25-80羽适合不同程度的定量分析。在这项研究中，一些简单的分析应用于约束Strombolian羽动力学的基本参数在其初始上升（130米）。羽流上升速率包括气体推力（>15 m s-1）和浮力状态（<15 m s-1），这反过来又控制了横向扩展速率和空气夹带速率。羽流前缘横向扩展的半角在气体推力状态下平均为7.3（±1.6）°，在浮力状态下平均为13.5（±1.6）°，相当于气体推力状态下的平均空气卷吸系数为0.06-0.12，浮力状态下的平均空气卷吸系数为0.22（±0.03）。这些因素也与羽流形态有关，包括喷流、初始羽流和热气流。一个“扎根热”的形式被观察到，并假定为中间的起始羽流和离散的热气流。羽流上升可以近似为幂律依赖于时间。根部热气流传播和夹带空气的速度接近离散的热，但上升的速度类似于起始羽流。在前视红外图像中可以看到螺旋运动和沉降现象。这些结果表明，紧急羽行为是渐进的和高度瞬态的。此外，这项研究还提供了经验证据，证明卷吸动力学在（1）气体推力与浮力驱动机制以及（2）羽流前锋与稳定羽流中存在本质上的不同。
[1] Imaging volcanic plumes is essential to provide an observational basis for understanding and modeling plume dynamics. During June-July 2004, ∼150 Strombolian ash plumes were imaged at Stromboli volcano, Italy, with a forward looking infrared radiometer (FLIR) thermal video camera (30 Hz). Of these, 25-80 plumes were suited for different levels of quantitative analyses. In this study some simple analyses are applied to constrain basic parameters for the dynamics of Strombolian plumes during their initial ascent (∼130 m). Plume rise rates covered both gas thrust (>15 m s -1 ) and buoyant regimes (<15 m s -1 ), which in turn controlled lateral spreading rates and air entrainment rates. The half angle of lateral spreading of the plume front averaged 7.3(±1.6)° for gas thrust regimes and 13.5(±1.6)° for buoyant regimes, equating to mean air entrainment coefficients of 0.06-0.12 for gas thrust regimes and 0.22(±0.03) for buoyant regimes. These factors were also linked to plume morphologies, which included jets, starting plumes and thermals. A "rooted thermal" form was observed and presumed as an intermediary between starting plumes and discrete thermals. Plume rise could be approximated by a power law dependence with time. Rooted thermals spread and entrained air at rates approaching those of a discrete thermal but rose at a rate similar to that of a starting plume. Phenomena including helical motion and sedimentation were visible in the FLIR imagery. These results demonstrate that emergent plume behavior is progressive and highly transient. Furthermore, this study offers empirical reinforcement that entrainment dynamics are intrinsically different in (1) gas thrust versus buoyantly driven regimes and (2) plume fronts versus steady plumes.