Direct Observations of Near‐Inertial Wave <i>ζ</i>‐Refraction in a Dipole Vortex
Leif N. Thomas, Luc Rainville, Olivier Asselin, W. R. Young, James B. Girton, Caitlin B. Whalen, Luca Centurioni, Verena Hormann
Abstract
Abstract Generated at large horizontal scales by winds, near‐inertial waves (NIWs) are inefficient at radiating energy without a shift to smaller wavelengths. The lateral scales of NIWs can be reduced by gradients in the Coriolis parameter ( β ‐refraction) or in the vertical vorticity ( ζ ‐refraction) or by strain. Here we present ship‐based surveys of NIWs in a dipole vortex in the Iceland Basin that show, for the first time, direct evidence of ζ ‐refraction. Differences in NIW phase across the dipole were observed to grow in time, generating a lateral wavelength that shrank at a rate consistent with ζ ‐refraction, reaching ∼ 40 km in 1.5 days. Two days later, a NIW beam with an ∼ 13 km horizontal and ∼ 200 m vertical wavelength was detected at depth radiating energy downward and toward the dipole's anticyclone. Strain, while significant in strength in the dipole, had little direct effect on the NIWs.