Résumé
In this paper, we first evaluate the ability of the European Centre for Medium Range Forecast operational analysis and the ERA-Interim reanalysis to capture the surface wind signature of tropical cyclones (TCs). In those products, the error on the TC position is typically similar to 150 km, cyclones are too big (similar to 250 km in ERA-Interim and >100 km in the operational analysis against similar to 50 km in observations) and the maximum wind speed is on average underestimated by 15-27 m.s(-1) for strong TCs. These biases are generally reduced with the increase of horizontal resolution in the operational analysis, but remain significant at T1279 (similar to 16 km).
We then assess the TCs oceanic temperature signature in two global eddy-permitting ocean reanalyses (GLORYS1 and GLORYS2) forced by the above atmospheric products. The resulting cold wake is on average underestimated by similar to 50% in the two oceanic reanalyses. This bias is largely linked to the underestimated TCs strength in the surface forcing, and the resulting underestimated vertical mixing. The overestimated TC radius also tends to overemphasize the Ekman pumping response to the cyclone. Underestimating vertical mixing without underestimating Ekman pumping results in the absence of the observed subsurface warming away from the TC tracks in the two reanalyses. Data assimilation only marginally contributes to reducing these errors, partly because cyclone signatures are not well resolved by the ocean observing system. Based on these results, we propose some assimilation and forcing strategies in order to improve the restitution of TC signatures in oceanic reanalyses. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.