Abstract Preferential particle orientation has been previously reported for desert dust and attributed on atmospheric electricity (Ulanowski et al., 2007). Depending on its strength, the total electric field within the dust layer can: (a) counteract the gravitational settling of large particles and (b) cause a preferential orientation of the non-spherical particles along the vertical direction (Fucks, 1958; Ulanowski et al., 2007). Both effects change the particle aerodynamics and impact radiative transfer. Here, we quantify the electrical and aerodynamic torques on the non-spherical prolate model that is frequently assumed for dust particles. The transport of these particles is assumed to only depend on the influence of electric and gravitational fields. We provide an analytical approximation for the calculation of the mean orientation angle of both charged and uncharged dust particles. We find that electric fields with strength greater than 60 kV/m are required for the alignment of particles up to 20 μ m in diameter, with the electric field lines. If the particles are moving with the same speed and in the same direction with the wind, the aerodynamic torque is zero and particle orientation along the electric field requires 1–2 orders of magnitude lower electric field strengths.

中文翻译：

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地球大气中垂直移动的非球形长颗粒尘埃粒子的方向

摘要 先前已经报道了沙漠尘埃的优先粒子取向，并归因于大气电（Ulanowski 等人，2007 年）。根据其强度，尘埃层内的总电场可以：(a) 抵消大颗粒的重力沉降和 (b) 导致非球形颗粒沿垂直方向优先取向（Fucks，1958；Ulanowski 等等，2007）。这两种效应都会改变粒子的空气动力学并影响辐射传递。在这里，我们量化了非球形扁长模型上的电气和空气动力扭矩，该模型经常为灰尘颗粒假设。假设这些粒子的传输仅取决于电场和引力场的影响。我们为带电和不带电尘埃粒子的平均取向角的计算提供了分析近似。我们发现，直径达 20 μm 的粒子与电场线对齐需要强度大于 60 kV/m 的电场。如果粒子以与风相同的速度和相同的方向移动，则空气动力扭矩为零，粒子沿电场取向需要低 1-2 个数量级的电场强度。