Constraining Tephra Aggregation Efficiency with Laboratory Experiments and Numerical Modeling

利亚考特兰博士已被授予美国国家科学基金会地球科学博士后奖学金，在格鲁吉亚理工学院开展研究和教育计划。这项研究将使用实验室实验和数值模拟相结合的方法，以更好地限制火山灰（火山灰）在火山羽最高区域的聚集速度。实验室实验将利用一个冰成核室，以参数化的火山灰聚合率在各种相对湿度和施加的电场强度。主要目的是提高我们对大气中火山灰对火山羽流中普遍存在的相对湿度条件以及这些羽流中电场存在的响应的理解。实验结果将是不同羽流条件（湿度、温度、电场）下颗粒尺寸分布预期变化的参数化。如果成功，这将使火山灰扩散模型能够使用近实时的气象数据来更好地预测颗粒在大气中的停留时间。研究结果将有助于限制火山灰灾害模型在危机应对方案中使用。这些模型的改进最终将提高航空安全性，并为远场火山灰对地面的影响制定更有效的减灾战略。火山灰沉降物是火山爆发最深远的危害，能够导致屋顶坍塌，污染供水，破坏关键设施，并威胁人和牲畜的健康。2010年冰岛埃亚菲亚德拉冰盖（Eyjafjallajökull）喷发，火山灰连续数天喷入大气层，导致欧洲大部分领空关闭，数十万旅客受到影响，航空业损失数十亿美元。这一事件的全球性质和高经济后果暴露了对火山灰在大气和地面分布的准确预测的迫切需要。虽然在过去的四十年里，对火山灰的运输和沉积的研究大大增加了我们对这些过程的理解，并使数值模型的发展能够模拟火山灰的扩散，但目前这一代火山灰模型还没有以有意义的方式捕捉到大量细小（63微米）的火山灰注入大气。火山灰的模型计算和真实分布之间的差异反映了大多数模型未能解释自然过程，这些自然过程迅速将火山喷出物的细灰部分作为较大聚集体的组成部分从大气中移除。为了促进对火山灰聚集的理解，同时培养大学生的模型素养和定量技能，将通过Vhub.org网络平台设计和实施一系列教育模块。VHub.org是火山建模和教育的在线资源。这项工作产生的火山灰聚集的数值参数化最终也将安装在Vhub.org上，以方便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.