The presence of coarse mineral dust in the atmosphere has been substantiated in several recent measurement campaigns, which include observations of particles up to and above 100 μm in diameter. Yet, atmospheric dust models either do not include particles larger than 20 μm or severely underestimate their concentrations. One possibility for the underestimated concentrations is that models do not represent enhancements of particle transport due to subgrid-scale topography. Here, large-eddy simulations are used in combination with Lagrangian particle tracking to assess the impact of gentle two-dimensional topography with 50 and 100 m elevation on the vertical transport of coarse dust in neutrally stratified conditions. The presence of topography significantly increases the likelihood that 5 and 20 μm particles reach several hundred meters in altitude. Further, topography increases this likelihood by orders of magnitude for larger 60 μm particles. Three mechanisms are observed to contribute to the increased vertical transport: a strong upward mean flow region on the uphill side of the topography, ejection of particles downwind of the topography crest, and enhanced vertical dispersion in the wake of the crest. The compounding effects of these mechanisms provide a pathway for coarse dust emitted from the surface to reach elevations where they can be further transported into the free atmosphere by large-scale motions such as convective plumes. While these findings are motivated by mineral dust observations, they are generally applicable to other heavy aerosols such as pollen.

中文翻译：

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温和的地形以数量级增加粗尘的垂直输送

最近的几次测量活动都证实了大气中存在粗矿物粉尘，其中包括对直径达 100 微米及以上的颗粒的观察。然而，大气尘埃模型要么不包括大于 20 μm 的颗粒，要么严重低估了它们的浓度。低估浓度的一种可能性是模型不代表由于亚网格尺度地形而导致的粒子传输增强。在这里，大涡模拟与拉格朗日粒子跟踪结合使用，以评估 50 米和 100 米高程的平缓二维地形对中性分层条件下粗尘垂直输送的影响。地形的存在显着增加了 5 和 20 微米粒子到达数百米高度的可能性。此外，对于较大的 60 μm 颗粒，形貌将这种可能性增加了几个数量级。观察到三种机制有助于增加垂直输运：地形上坡侧的强烈向上平均流区域、地形波峰下风向的粒子喷射以及波峰后增强的垂直扩散。这些机制的复合效应为从地表排放的粗尘到达高地提供了一条途径，在那里它们可以通过对流羽流等大规模运动进一步输送到自由大气中。虽然这些发现是由矿物尘埃观察激发的，但它们通常适用于其他重气溶胶，如花粉。观察到三种机制有助于增加垂直输运：地形上坡侧的强烈向上平均流区域、地形波峰下风向的粒子喷射以及波峰后增强的垂直扩散。这些机制的复合效应为从地表排放的粗尘到达高地提供了一条途径，在那里它们可以通过对流羽流等大规模运动进一步输送到自由大气中。虽然这些发现是由矿物尘埃观察激发的，但它们通常适用于其他重气溶胶，如花粉。观察到三种机制有助于增加垂直输运：地形上坡侧的强烈向上平均流区域、地形波峰下风向的粒子喷射以及波峰后增强的垂直扩散。这些机制的复合效应为从地表排放的粗尘到达高地提供了一条途径，在那里它们可以通过对流羽流等大规模运动进一步输送到自由大气中。虽然这些发现是由矿物尘埃观察激发的，但它们通常适用于其他重气溶胶，如花粉。并在波峰后增强了垂直扩散。这些机制的复合效应为从地表排放的粗尘到达高地提供了一条途径，在那里它们可以通过对流羽流等大规模运动进一步输送到自由大气中。虽然这些发现是由矿物尘埃观察激发的，但它们通常适用于其他重气溶胶，如花粉。并在波峰后增强了垂直扩散。这些机制的复合效应为从地表排放的粗尘到达高地提供了一条途径，在那里它们可以通过对流羽流等大规模运动进一步输送到自由大气中。虽然这些发现是由矿物尘埃观察激发的，但它们通常适用于其他重气溶胶，如花粉。