Observed equatorward propagation and chimney effect of near-inertial
waves in the mid-latitude ocean
Abstract
The propagation characteristics of near-inertial waves (NIWs) and how
mesoscale and submesoscale processes affect the waves’ vertical
penetration (i.e., the chimney effect) are investigated using
observations from a mooring array located in the northeast Atlantic. The
year-long observations show that near-inertial motions are mainly
generated by local wind forcing and that they radiate predominantly
downward following several strong wind events. Once below the mixed
layer, NIWs preferentially propagate equatorward primarily in the form
of low modes. High-mode NIWs, however, are most likely dissipated
locally near the base of the mixed layer. Enhanced near-inertial kinetic
energy and vertical shear are found only in mesoscale anticyclones with
Rossby number of O(0.1). By contrast, submesoscale motions with order
one Rossby number have little effect on the trapping and vertical
penetration of NIWs, due to their smaller horizontal scales and confined
vertical extent compared to mesoscale eddies.