LIDAR Studies of Small-Scale Lateral Dispersion in the Ocean

Sponsored in part by ONR award MIPR-N0001411WX21010.

Our long-term goal is to better understand lateral mixing processes in the ocean on scales of 10 m to 10 km (i.e., the submesoscale). We aim to understand the underlying mechanisms and forcing, as well as the temporal, spatial, and scale variability of such mixing. The research will contribute to fundamental knowledge of ocean dynamics at these scales, and to efforts to properly parameterize sub-grid scale mixing and stirring in numerical models. Ultimately our research also will enhance modeling and understanding of upper ocean ecosystems, since the flow of nutrients and plankton depends on stirring and mixing at these scales. One objective of our work is to determine the extent to which shear dispersion -- the interaction of vertical mixing with vertical shear -- can explain lateral dispersion at scales of 10 m to 10 km. A second objective is to determine whether slow but persistent vortices enhance the stirring attributable to shear dispersion. We also share the overall objectives of the Lateral Mixing DRI to try to determine the extent to which submesoscale stirring is driven by a cascade of energy down (in wavelength) from the mesoscale versus a propagation of energy upwards from small mixing events (e.g., via generation of vortices). A key technical goal of our work is to develop the use of airborne LIDAR surveys of evolving dye experiments as a tool for studying submesoscale lateral dispersion. Our approach is to release dye patches on an isopycnal surface in the seasonal pycnocline, and to survey their evolution for periods of 1 to 6 days in collaboration with other investigators in the DRI. Drogues released with the dye not only help with tracking, but also give valuable measurements of the shear/strain field on the outer scale of the patches. Lagrangian floats released with the dye patches give measurements of vertical shear and strain following the patch. The dye patches are sampled not only with towed instruments from ships, but also with airborne LIDAR.