Constraining Tephra Aggregation Efficiency with Laboratory Experiments and Numerical Modeling

Leah Courtland博士被授予美国国家科学基金会地球科学博士后奖学金，在乔治亚理工学院开展一项研究和教育计划。这项研究将使用实验室实验和数值模拟相结合的方法来更好地限制火山羽流最上层区域火山灰聚集的速度。实验室实验将利用一个冰成核室来参数化在各种相对湿度和外加电场强度下的碲聚集率。主要目标是提高我们对大气中水蒸气对火山羽流中普遍存在的相对湿度条件的反应的理解，以及这些羽流中电场的存在。实验结果将是不同羽流条件（湿度、温度、电场）下粒径分布预期变化的参数化。如果成功的话，这将允许粒子弥散模型使用近实时气象数据来更好地预测粒子在大气中的停留时间。研究结果将有助于约束在危机应对情景中使用的麻风危害模型。这些模型的改进应最终导致航空安全的提高和更有效的减灾战略，以应对对地面的远场辐射影响。辐射尘是火山爆发影响最深远的危害，能够造成屋顶坍塌，污染供水，破坏关键设施，并威胁到人和牲畜的健康。2010年冰岛Eyjafjallajökull火山喷发，火山灰向大气中喷射了数天，导致欧洲大部分空域关闭，影响了数十万旅客，给航空业造成了数十亿美元的损失。这一事件的全球性质和严重的经济后果表明，迫切需要对大气和地面上的麻风分布进行准确预报。虽然过去四十年来对火山灰的迁移和沉积的研究大大增加了我们对这些过程的理解，并使模拟火山灰扩散的数值模型得以发展，但目前一代的火山灰模型还没有以有意义的方式捕捉到大量细（63微米）火山灰注入大气的过程。模型计算结果与火山灰的真实分布之间的差异反映了大多数模型未能考虑到从大气中迅速除去火山喷出物的细灰部分作为较大聚集物的组成部分的自然过程。为了促进对灰烬聚集的理解，同时培养大学生的模式素养和定量技能，Vhub.org将通过网络平台设计和实施一系列教育模块。VHub.org是一个火山建模和教育的在线资源。从这项工作中得出的灰分聚集的数值参数化最终也将安装在Vhub.org上，以便于更大的科学界使用该模型。

Dr. Leah Courtland has been awarded an NSF Earth Science Postdoctoral Fellowship to carry out a research and education plan at Georgia Institute of Technology. This study will use a combination of laboratory experiments and numerical modeling to better constrain the rate of tephra (volcanic ash) aggregation in the uppermost regions of volcanic plumes. Laboratory experiments will utilize an ice nucleation chamber to parameterize the rate of tephra aggregation under a variety of relative humidities and applied electric field strengths. The main goal is to improve our understanding of the response of tephra in the atmosphere to the relative humidity conditions prevalent in volcanic plumes and the presence of an electric field within these plumes. The result of experiments will be a parameterization of the expected change in particle size distribution for varying plume conditions (humidity, temperature, electrical field). If successful, this will allow tephra dispersion models to use near-real- time meteorological data to better forecast particle residence time in the atmosphere. Research results will help to constrain tephra hazard models used in crisis response scenarios. Improvement in these models should ultimately lead to increased aviation safety and more effective hazard mitigation strategies for far-field tephra impacts on the ground.Tephra fallout is the most far reaching hazard of volcanic eruptions, capable of causing roof collapse, polluting water supplies, damaging critical facilities, and threatening the health of people and livestock. The 2010 eruption of Eyjafjallajökull in Iceland spewed ash into the atmosphere for days, effectively shutting down most of European air space, affecting hundreds of thousands of travelers, and costing the aviation industry billions of dollars. The global nature and high economic consequence of this event expose an urgent need for accurate forecasts of the distribution of tephra in the atmosphere and on the ground. While the study of the transport and sedimentation of volcanic ash over the last forty years has greatly increased our understanding of these processes and enabled the development of numerical models to simulate tephra dispersion, the injection of large volumes of fine (63 um) ash into the atmosphere is not yet captured in a meaningful way by the current generation of tephra models. The discrepancy between model calculations and the true distribution of tephra reflects the failure of the majority of models to account for natural processes that rapidly remove the fine ash fraction of volcanic ejecta from the atmosphere as constituent pieces of larger aggregates. To facilitate understanding of ash aggregation while fostering model literacy and quantitative skills building among university students, a series of educational modules will be designed and implemented via the Vhub.org web platform. VHub.org is an online resource for volcano modeling and education. The numerical parameterization of ash aggregation to result from this work will ultimately be installed on Vhub.org as well, in order facilitate use of the model by the larger scientific community.