Electrostatic fields in dust devils: an analog to Mars

Mars has a dynamic atmosphere with dust devils and global dust storms. It is possible that dust devils on this planet may be electrical in nature. In order to understand the electrical nature of Martian dust storms, terrestrial dust devils are treated as an analog, and measurements of terrestrial dust devil electrostatic fields are obtained. Specifically, the construction of an electrometer designed to measure the anticipated large fields in the convective features is described. The large electric fields (E-fields) in dust devils have saturated previous test instruments, thus foiling previous attempts to obtain internal dust devil E-fields. Once the electrometer was built and calibrated, unique measurements of the horizontal E-field within a well-formed dust devil in the Mojave desert were obtained. It is found that peak horizontal E-field values exceeded 100 kV/m within the dust devils. Each transit through the dust devil (i.e., from outside to the dust devil center and back out) created a consistent "twin-peak" horizontal E-field signature, with E-fields having the distinct minimum in the dust devil center. Using a model, the electric dipole moment of the dust devil was characterized via a comparison of observed and modeled E-fields. The twin-peak signature is also a feature found in the model as well. The electric dipole moment was found to be -0.168 C/spl middot/m, with the negative sign indicative of a downward-directed dipole moment.