Observed Equatorward Propagation and Chimney Effect of Near‐Inertial Waves in the Midlatitude Ocean

Abstract

The propagation characteristics of near‐inertial waves (NIWs) and how mesoscale and submesoscale processes affect the waves' vertical penetration 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 equatorward and downward following several strong wind events (wind stress ≳0.5 N m−2). Observational estimates of horizontal group speed typically exceed those of vertical group speed by two orders of magnitude, consistent with predictions from the dispersion relation. 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, shorter time scales, and confined vertical extent compared to mesoscale eddies.

Widespread Intensified Pycnocline Turbulence in the Summer Stratified Yellow Sea

“…It is clear from Figure 9a that the observed strong turbulence was located below the strongest stratification at depths of 30-40 m. Instead, S 2 peaked right in (instead of below) the strongest stratification layer (∼23 m depth, Figure 9b). Previous studies have also documented that the near-inertial shear was most likely quickly dissipated at the base of the mixed layer (e.g., Yu et al, 2022). There was a secondary large shear layer lying below the isopycnal of 25 kg m −3 at depth of ∼40 m during the first 8 hr.…”

“…H08 was characterized by moderate wind speed (∼8 m s −1 ) during the observation period, the wind generally showed a quite intermittent feature during the 1-month period since August 13. The wind energy flux into near-inertial motions can be dominated by such intermittent events with duration of several days (Yu et al, 2022), resulting in prevailing near-inertial responses in the mixed layer (Figure 7b).…”

Can we observe near-inertial waves by using lowered Acoustic Doppler Current Profiler?

“…Four casts within 24 hours are sufficient to resolve the amplitude by 0.05 ms −1 and the phase by π/12 = 1 hour. As demonstrated by mooring observation (Yu et al, 2022), the internal waves below mixed layers are observed in response to wind events. The wave propagates at a speed of 50 to 80 m/day (Yu et al, 2022).…”

“…As demonstrated by mooring observation (Yu et al, 2022), the internal waves below mixed layers are observed in response to wind events. The wave propagates at a speed of 50 to 80 m/day (Yu et al, 2022). It is quite plausible to observe by ship these near-inertial waves at around 500 m depth after 6 to 10 days after a storm.…”

“…One is that these waves occur intermittently in space and time (e.g. Yu et al, 2022). Most of large amplitude nearinertial waves in the upper ocean are observed in response to surface events such as passage of tropical cyclones.…”