Topographic Rossby Waves in the Arctic Ocean's Beaufort Gyre

Abstract

AbstractA 5‐year long time series of temperature and horizontal velocity in the Arctic Ocean's Beaufort Gyre is analyzed with the aim of understanding the mechanism driving the observed variability on timescales of tens of days (i.e., subinertial). We employ a coherency/phase analysis on the temperature and horizontal velocity signals, which indicates that subinertial temperature variations arise from vertical excursions of the water column that are driven by horizontal motions across the sloping seafloor. The vertical displacements of the water column (recorded by the temperature signal) show a bottom‐intensified signature (i.e., decay toward the surface), while horizontal velocity anomalies are approximately barotropic below the main halocline. We show that the different characteristics in vertical and horizontal velocities are consistent with topographic Rossby wave theory in the limit of weak vertical decay. In essence, a linearly decaying vertical velocity profile implies that the whole water column is stretched/squashed uniformly with depth when water moves horizontally across the bottom slope. Thus, for the uniform stratification of the deep water column, the response in the relative vorticity field (ensuring conservation of potential vorticity) is also uniform with depth, leading to the observed barotropic horizontal velocity changes. The prevalent topographic Rossby wave activity is discussed in context with Beaufort Gyre spin‐up, dissipation, and stabilization.