Seismometer Detection of Dust Devil Vortices by Ground Tilt

TL;DR

This study demonstrates that seismic ground tilt measurements can detect dust devils and vortices on desert surfaces, providing a sensitive method for identifying such atmospheric phenomena through modeling and analysis.

Contribution

It introduces a simple quasi-static point-load model to interpret seismic signals caused by dust devils, highlighting ground tilt as a sensitive detection method.

Findings

Seismic signals correlate with dust devil presence and pressure drops.

Tilt signals can be modeled with a point-load approximation of vortex pressure.

Large dust devils produce signals comparable to small vehicle weights.

Abstract

We report seismic signals on a desert playa caused by convective vortices and dust devils. The long-period (10-100s) signatures, with tilts of ~10$^{-7}$ radians, are correlated with the presence of vortices, detected with nearby sensors as sharp temporary pressure drops (0.2-1 mbar) and solar obscuration by dust. We show that the shape and amplitude of the signals, manifesting primarily as horizontal accelerations, can be modeled approximately with a simple quasi-static point-load model of the negative pressure field associated with the vortices acting on the ground as an elastic half space. We suggest the load imposed by a dust devil of diameter D and core pressure {\Delta}Po is ~({\pi}/2){\Delta}PoD$^2$, or for a typical terrestrial devil of 5 m diameter and 2 mbar, about the weight of a small car. The tilt depends on the inverse square of distance, and on the elastic properties of the ground, and the large signals we observe are in part due to the relatively soft playa sediment and the shallow installation of the instrument. Ground tilt may be a particularly sensitive means of detecting dust devils. The simple point-load model fails for large dust devils at short ranges, but more elaborate models incorporating the work of Sorrells (1971) may explain some of the more complex features in such cases, taking the vortex winds and ground velocity into account. We discuss some implications for the InSight mission to Mars.