Detecting and characterizing Ekman currents in the Southern Ocean

• Published in: Journal of Physical Oceanography
• Main Authors: Roach, CJ, Phillips, HE, Bindoff, NL, Rintoul, SR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2015
• Subjects: Earth Sciences; Oceanography; Physical Oceanography; Antarctic; Drake Passage; Kerguelen; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.1175/JPO-D-14-0115.1; http://ecite.utas.edu.au/99058

This study presents a unique array of velocity profiles from Electromagnetic Autonomous Profiling Explorer(EM-APEX) profiling floats in the Antarctic Circumpolar Current (ACC) north of Kerguelen. The authors usethese profiles to examine the nature of Ekman spirals, formed by the action of thewind on the oceans surface, inlight of Ekmans classical linear theory and more recent enhancements. Vertical decay scales of the Ekmanspirals were estimated independently from current amplitude and rotation. Assuming a vertically uniformgeostrophic current, decay scales from the Ekman current heading were twice as large as those from the currentspeed decay, indicating a compressed spiral, consistent with prior observations and violating the classical theory.However, if geostrophic shear is accurately removed, the observed Ekman spiral is as predicted by classicaltheory and decay scales estimated from amplitude decay and rotation converge toward a common value. Nostatistically robust relationship is found between stratification and Ekman decay scales. The results indicate thatcompressed spirals observed in the Southern Ocean arise from aliasing of depth-varying geostrophic currentsinto the Ekman spiral, as opposed to surface trapping of Ekman currents associated with stratification, andextends the geographical area of similar results from Drake Passage (Polton et al. 2013). Accounting for thiseffect, the authors find that constant viscosity Ekman models offer a reasonable description of momentummixing into the upper ocean in the ACC north of Kerguelen. These results demonstrate the effectiveness of anew method and provide additional evidence that the same processes are active for the entire Southern Ocean.