Katy M. Christensen, Alison R. Gray, Stephen C. Riser

Published in Journal of Geophysical Research, January 2024

Global estimates of mesoscale vertical velocity remain poorly constrained due to a historical lack of adequate observations on the spatial and temporal scales needed to measure these small magnitude velocities. However, with the wide-spread and frequent observations collected by the Argo array of autonomous profiling floats, we can now better quantify mesoscale vertical velocities throughout the global ocean. We use the underutilized trajectory data files from the Argo array to estimate the time evolution of isotherm displacement around a float as it drifts at 1,000 m, allowing us to quantify vertical velocity averaged over approximately 4.5 days for that depth level. The resulting estimates have a non-normal, high-peak, and heavy-tail distribution. The vertical velocity distribution has a mean value of (1.9 ± 0.02) × 10⁻⁶ m s⁻¹ and a median value of (1.3 ± 0.2) × 10⁻⁷ m s⁻¹, but the high-magnitude events can be up to the order of 10⁻⁴ m s⁻¹. We find that vertical velocity is highly spatially variable and is largely associated with a combination of topographic features and horizontal flow. These are some of the first observational estimates of mesoscale vertical velocity to be taken across such large swaths of the ocean without assumptions of uniformity or reliance on horizontal divergence.

Christensen, K. M., Gray, A. R., & Riser, S. C. (2024). Global estimates of mesoscale vertical velocity near 1,000 m from Argo observations. Journal of Geophysical Research: Oceans, 129, e2023JC020003. https://doi.org/10.1029/2023JC020003