Argo array observation of ocean heat content changes induced by tropical cyclones in the north Pacific

Abstract

In situ observations from the autonomous Argo float array are used to assess the basin-averaged ocean heat content change driven by tropical cyclones (TCs) in the North Pacific for 2000–2008. A new statistical approach based on pairs of profiles before and after each TC event is employed here to estimate the near-surface and subsurface heat content changes. Previous studies have suggested a dominant role for vertical mixing in the SST cooling response during TC passages. The Argo float observations show that, under strong TCs (greater than or equal to category 4), the subsurface warming expected from vertical mixing occurs with comparable magnitude to near-surface cooling. However, when weak TCs (less than or equal to category 3, which are about 86% of the total of TCs) were also considered, the subsurface warming was not detectable in the Argo data set, while near-surface cooling was still significant. Therefore, these results suggest that air-sea heat exchange and (upward) vertical advection likely play a somewhat greater role in the case of weak TCs. Additionally, Argo observations suggest that the restoring time scale of the near-surface heat content is greater than 30 days, which may be compared with the approximately 10 day time scale for the restoration of sea surface temperature. The mixed layer temperature and mixed layer depth evolutions also estimated from Argo data support the notion that only a thin surface layer is restored quickly to pre-TC conditions, while the rest of the cooled near-surface layer retained the TC-induced response for a good deal longer.