On the Ambiguity of Oceanic Eddy Polarity

Abstract

Polarity is a fundamental feature of oceanic eddies, which defines many aspects of its hydrodynamics and thermodynamics. Polarity ambiguity is a challenging and sometimes puzzling issue for the classification of eddies and analysis of their dynamics. Here, we propose a new methodology combining drifter-measured currents and temperatures to evaluate the validity of altimeter-derived eddy polarity. Different from previous schemes based purely on assessing oceanic temperature ambiguity of eddies from either satellite or Argo observations, our approach integrates the concurrent vector flow and surface temperature measured by drifters riding on altimeter-tracked eddies. The idea is to examine the consistency between the rotation of drifter trajectory and the spinning of eddy motion on the assumption that the looping and circulating directions are identical for a normal eddy and otherwise for an “ambiguous” or “abnormal” one. For a special class of radial drifter trajectory with respect to the eddy centroid, the temperature trend along its path is used to judge its polarity, that is, warmer toward the core for a normal anticyclonic eddy and colder for cyclonic. Our results reveal that many eddies previously classified as “abnormal” are in fact dynamically or thermally ambiguous due to distortions in their upper-layer structures rather than being genuinely misclassified by altimeter. After excluding such ambiguous cases, only ∼3% of eddies show polarity inconsistency in both aspects. These findings suggest that altimeter-derived eddy polarity is highly reliable, and that combining a multi-parameter, Lagrangian-informed approach offers more accurate interpretations of eddy structures by distinguishing intrinsic anomalies from superficial distortions.