Introduction to the Special Issue on NISKINe

Near-inertial internal waves (NIW) constitute a dominant mode of high-frequency variability in the ocean’s interior, comprising about half the kinetic energy in the ocean at most sites (and even more in the winter beneath storm tracks; Alford et al., 2016). Over the last decade there has been a significant focus in the physical oceanographic community on internal tides, which produce large thermocline displacements, affect sound propagation, and control some hotspots of elevated turbulent mixing. Near-inertial internal gravity waves, which are primarily generated not by tides but by winds, are of similar importance, providing comparable kinetic energy and the vast majority of the shear variance, and likely leading to a substantial amount of turbulent mixing. Significant deficiencies remain in our understanding of the physical processes that determine their generation, evolution, and destruction.