Alignment of atmospheric dust observed by high-sensitivity optical polarimetry

Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode showed dichroic extinction, indicating the presence of vertically aligned particles in the atmosphere. It is postulated that the alignment was due to an electric field of the order of 1 kV/m or greater. Two alternative mechanisms for the origin of the field are examined, including the effect of reduced atmospheric conductivity and the presence of charged dust.