Uncertainties in Altimetry Observations of Eddy Changes Induced by Tropical Cyclones

Abstract

Abstract The effects of tropical cyclones (TCs) on preexisting eddies are generally quantified by comparing post-TC and pre-TC altimetry-based eddy amplitudes and radii. The dynamical and technical uncertainties in this quantification have been revealed by the altimetry-based and simulated eddy characteristics of five cyclonic ocean eddies (COEs) and two anticyclonic ocean eddies (AOEs). Although demonstrated by eddy cases, both the uncertainties should be universal in principle. The dynamical uncertainty primarily arises from the highly variable eddy characteristics associated with the post-TC quasigeostrophic evolutions driven by the inevitable pattern discrepancy between TC-injection and preexisting eddy’s potential vorticity (PV). The technical uncertainty is due to the artificial smoothness in the altimetry-based eddy characteristics produced by the mismatch between sparse data interpolation and sudden injection of TC-induced effects. Beyond the uncertainties, the amplitudes and radii of both the COEs and AOEs were damped directly by a rectilinear-track TC. After the TC passage, the COEs may strengthen again or remain in the damped state, depending on whether the COEs can absorb the TC-injected PV. By contrast, the AOEs remained in the damped state because the TC-injected positive PV cannot excite them to enhance and enlarge. More importantly, the above damped state of the perturbed COEs and AOEs may be the result of the developing geostrophic turbulence, not meaning the decay of the TC-induced effects. This fact, together with the dynamical and technical uncertainties, implies that the previously used quantification may significantly underestimate the TC-induced effects. Significance Statement Typhoons/hurricanes inject their effects on ocean eddies and further modulate the ocean circulation and climate by the accumulated effects. These effects are generally quantified by altimetry observations. Two uncertainties in this quantification are illustrated by using several eddy cases. The first uncertainty is caused by the eddy evolution, while the second is by the artificial smoothness in the altimetry-based eddy characteristics. These findings suggest that the effects of typhoons/hurricanes may be underestimated due to the two uncertainties and underscore that a new method based on physical understanding is necessary to quantify these effects.