Lobe-Cleft Instabilities on a river plume front

Abstract

These data accompany a paper submitted to Geophysical Research Letters. The abstract is below.

Gravity currents represent a broad class of geophysical flows including turbidity currents, powder avalanches, pyroclastic flows, sea-breeze fronts, haboobs and river plumes. A defining feature in many gravity currents is the formation of three-dimensional lobes and clefts along the front and researchers have sought to understand these ubiquitous geophysical structures for decades. The prevailing explanation is based largely on early laboratory and numerical model experiments at much smaller scales, which concluded that lobes and clefts are generated due to hydrostatic instability exclusively in currents propagating over a non-slip boundary. Recent studies suggest that frontal dynamics change as the flow scale increases, but no measurements have been made that sufficiently resolve the flow structure in full-scale geophysical flows. Here, we use thermal infrared and acoustic imaging of a river plume to reveal the three-dimensional structure of lobes and clefts formed in a geophysical gravity current front. The observed lobes and clefts are generated at the front in the absence of a non-slip boundary, contradicting the prevailing explanation. The observed flow structure is consistent with a alternative formation mechanism, which predicts that the lobe scale is inherited from subsurface vortex structures.