SGER: Documenting the Transient Nature of Natural Free Convection in Groundwater

2008年阿拉伯联合酋长国（UAE）极端降水事件后的sabkha的地球物理成像显示了自然地下水环境中自由对流流动过程的第一个令人信服的证据。成像模式与降水引起的岩盐壳再溶解和预先存在的对流模式相一致；这些手指的分布与在实验室实验和数值模拟中观察到的相似。自然自由对流对热和溶质在一系列水文地质环境中的传输很重要，人们对它的研究已经有一个多世纪了，但几乎完全是在理论、数值模型和实验室实验中进行的。目前，对对流不稳定性的增长和衰减知之甚少，因为大多数研究都假设了稳态条件。为了解决对流起源和持续的关键问题，以及它们相关的空间和时间尺度，解决不同相互作用机制的瞬态性质是至关重要的。我们的阿联酋现场站点是解决这些知识差距的理想地点。降水记录表明，这个地点的指状活动可能每十年才开始一次，在干旱的年份里，盐岩地壳会逐渐形成。我们的试点数据展示了监测密度指法动态性质的独特机会。我们建议将延时地球物理、水文和地球化学测量与初步水文建模相结合。探索性研究将为这一重要领域提供变革性的进展。研究结果将通过研究论文和会议报告进行传播，并将为包括全面建模工作在内的后续研究计划奠定基础。

Geophysical imaging of a sabkha in the United Arab Emirates (UAE) following an extreme precipitation event in 2008 shows the first compelling evidence of free convection flow processes in a natural groundwater setting. The imaged pattern is consistent with fingering caused by precipitation-induced redissolution of a halite crust and a pre-existing convection pattern; the distribution of these fingers is similar to those observed in lab experiments and numerical simulations. Natural free convection, which is important for heat and solute transport across a range of hydrogeologic settings, has been studied for over a century but almost entirely in theory, numerical models, and laboratory experiments. Currently, very little is known about the growth and decay of convective instabilities because most research assumes steady state conditions. In order to resolve key questions about origins and persistence of convection, as well as their associated spatial and temporal scales, it is vital to resolve the transient nature of different interacting regimes.Our UAE field site is an ideal location to address some of these knowledge gaps. Precipitation records suggest that fingering at this site may only be initiated once every decade with a halite crust building up during dryer years. Our pilot data demonstrate the unique opportunity to monitor the dynamic nature of density fingering. We propose to integrate time-lapse geophysical, hydrological, and geochemical measurements with preliminary hydrological modeling. The exploratory research will provide a transformative advance for this important field. The results will be disseminated through research papers and conference presentations and will form the foundation for a continued research program including a full-scale modeling effort.