Global estimates of mesoscale vertical velocity near 1000 m from Argo
observations
Abstract
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 from the Argo array to
estimate the time evolution of isotherm displacement around a float as
it drifts at 1000 dbar, allowing us to quantify vertical velocity
averaged over approximately 4.5 days for that pressure 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.