Alignment of atmospheric mineral dust due to electric field

[摘要] Optical polarimetry observations on La Palma, Canary Islands, during aSaharan dust episode show dichroic extinction indicating the presence ofvertically aligned particles in the atmosphere. Modelling of the extinctiontogether with particle orientation indicates that the alignment could havebeen due to an electric field of the order of 2 kV/m. Two alternativemechanisms for the origin of the field are examined: the effect of reducedatmospheric conductivity and charging of the dust layer, the latter effectbeing a more likely candidate. It is concluded that partial alignment may bea common feature of Saharan dust layers. The modelling indicates that thealignment can significantly alter dust optical depth. This "Venetian blindeffect" may have decreased optical thickness in the vertical direction byas much as 10% for the case reported here. It is also possible that thealignment and the electric field modify dust transport.

[学科分类] 大气科学