Gravity currents are ubiquitous geophysical flows that transport everything from sediment to contaminants to buoyancy to snow, and that have important environmental impacts due their roles in diverse fields such as weather, sedimentology, lake and reservoir water quality, building ventilation and ocean circulation. However, the majority of research in this vast field is based on laboratory and model experiments at Reynolds numbers that are orders of magnitude smaller than those of the geophysical flows of interest and there are very few quantitative field measurements that resolve these flows with sufficient detail for direct comparison. A recent pilot study on the Merrimack River plume, a gravity current of great importance to the coastal ecosystem, revealed complex structures along the front associated with frontal instability. The observations were made possible using a new front-following infrared remote sensing platform and will be used to better understand the dynamics of geophysical scale gravity currents.
The video above is created from thermal images of the Merrimack River plume (MA) acquired from an infrared camera suspended 50 m above the ocean and tethered to the boat you see in the image. The boat is being carried seaward at almost 2 km/hr by the plume front. The plume is warmer than the ocean water and shows up as lighter gray tones in the IR images.