Lifting particles in martian dust devils by pressure excursions

The passage of a dust devil vortex goes along with a pressure reduction above ground. This leads to a sub-soil overpressure. It has been suggested that this enhances the lift on particles and facilitates dust entrainment by dust devils. We quantify the necessary pressure difference to lift fine sand from sand beds with thickness of 50, 150, and 250 mm in laboratory experiments with basalt samples consisting of 63-125 mu m grains. The absolute pressure was varied between 1,300 and 3,600 Pa. In general, a pressure differences of about 30 Pa per mm depth is needed to lift sand grains. With slight systematic variations this is in agreement to simply accounting for the weight of a lifted particle layer. On Mars observed absolute pressure difference are several Pa. This limits particle lift to a layer smaller than 100 mu m. However, it clearly allows Delta p lifting if the top layer has a decreased permeability. This might be the case for dust layers sitting on top of a coarse grained sand bed. These measurements support the idea of enhanced dust entrainment due to the Delta p-effect in Martian dust devils under certain conditions.