吸附液体和物质密度对跃移阈值的影响：来自实验室和风洞实验的启示
The Effect of Adsorbed Liquid and Material Density on Saltation Threshold: Insight from Laboratory and Wind Tunnel Experiments
摘要：
跃移阈值是泥沙运移的最小风速，是风沙过程的一个基本参数。液体的存在，如地球上的水或泰坦上的甲烷，可能会在很大程度上影响阈值。沉积物密度对确定阈值也至关重要。在这里，我们提供了用于研究地球，泰坦，火星和金星条件的常见风洞材料的密度和水含量的定量数据。低密度材料的测量密度值高于文献值，而对于高密度材料，没有这种差异。我们还发现，低密度的材料有更高的含水量和更长的大气平衡时间尺度相比，高密度的沉积物。在Titan风洞中，我们用标准核桃壳（125-150 μm，质量含水量7.2%）和干燥核桃壳（质量含水量1.7%）进行了阈值实验。两种情况下的阈值结果几乎相同，这表明在本实验制度下，湿度对核桃壳阈值的影响可以忽略不计。当水含量低于11.0%时，颗粒间力由吸附力主导，而在较高值时，颗粒间力由大得多的毛细管力主导。对于具有低平衡水含量的材料，如石英砂，毛细管力占主导地位。当颗粒间力主要由吸附力控制时，阈值不随相对湿度（RH）的增加而增加。只有当颗粒间力主要由毛细管力时，阈值才开始随着RH/水含量的增加而增加。由于托林具有低甲烷含量（饱和时为0.3%，Curtis等人，2008年），我们相信托林会表现出类似的石英砂时，受到甲烷水分。[摘要摘要]
英文摘要：
Saltation threshold, the minimum wind speed for sediment transport, is a fundamental parameter in aeolian processes. The presence of liquid, such as water on Earth or methane on Titan, may affect the threshold values to a great extent. Sediment density is also crucial for determining threshold values. Here we provide quantitative data on density and water content of common wind tunnel materials that have been used to study conditions on Earth, Titan, Mars, and Venus. The measured density values for low density materials are higher compared to literature values, whereas for the high density materials, there is no such discrepancy. We also find that low density materials have much higher water content and longer atmospheric equilibration timescales compared to high density sediments. In the Titan Wind Tunnel, we performed threshold experiments with the standard walnut shells (125-150 μm, 7.2% water by mass) and dried walnut shells (1.7% water by mass). The threshold results for the two scenarios are almost the same, which indicates that humidity had a negligible effect on threshold for walnut shells in this experimental regime. When the water content is lower than 11.0%, the interparticle forces are dominated by adsorption forces, whereas at higher values the interparticle forces are dominated by much larger capillary forces. For materials with low equilibrium water content, like quartz sand, capillary forces dominate. When the interparticle forces are dominated by adsorption forces, the threshold does not increase with increasing relative humidity (RH). Only when the interparticle forces are dominated by capillary forces does the threshold start to increase with increasing RH/water content. Since tholins have a low methane content (0.3% at saturation, Curtis et al., 2008), we believe tholins would behave similarly to quartz sand when subjected to methane moisture. [abridged abstract]
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