Roles of SST anomalies on winter turbulent heat fluxes in the eastern Kuroshio-Oyashio Confluence Region: Influences of Kuroshio bifurcation
| A03-K9. Roles of SST anomalies on winter turbulent heat fluxes in the eastern Kuroshio-Oyashio Confluence Region: Influences of Kuroshio bifurcation | |
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| PI | Shusaku SUGIMOTO*(Assistant Professor, Tohoku University) |
[Doctral degree: *Oceanography]
Introduction
The Kuroshio/Kuroshio-Oyashio Confluence (KOC) region is characterized by vigorous heat release related to turbulent heat flux (THF; sum of sensible and latent heat fluxes) from ocean to atmosphere during winter (Fig. 1) and one of extremely large THF-release regions in the world’s oceans. Numerous authors have shown their interest in variable THF, and they have reported that the heat flux exchanges between ocean and atmosphere over the KOC region affect various atmospheric phenomena such as storm-track activity and cloud distributions.
The previous statistical studies have presented that the surface wind is primarily responsible for the determination of THF over the extratropical ocean. On the other hand, a few authors pointed a positive correlation between winter sea surface temperature (SST) and upward THF in the KOC region; more active upward heat fluxes on the warmer SST area. Recent study by Sugimoto and Hanawa (2011) showed that the THF in the western part of KOC (wKOC, displayed in Fig. 2) was determined by the SST, formed thorough activities of warm eddies detached northward from the Kuroshio Extension; SSTs takes positive (negative) anomalies when more (less) warm eddies are distributed there, associated with a more convoluted (straight) Kuroshio Extension path. Figure 2 displays the THF averaged for December 2004/February 2005. Vigorous heat is released over the eastern part of KOC (east of 150E; eKOC), but the value in wKOC is small. It is expected that the THF variations in the KOC region are different in west and east.
Purpose
We investigate the THF variations in the eKOC, and assess a role of SST for the determination of THF, by using observed dataset. In addition, we try to reveal the SST variations in the eKOC, by using the temperature-salinity profiles and hindcast model output.Research plan
- (i) Temporal behavior of THF in the eKOC
Firstly, we investigate temporal behavior of THF in the eKOC, by using the objectively analyzed air-sea flux dataset (OAFlux) with a relatively high spatial resolution, the products of which are a combination of observed satellite-derived data and reanalysis data. Then, we clarify the difference between the eKOC of our interest and the wKOC in THF, in terms of its phase and amplitude.
Generally, the THF reflects three variables of SST, surface air temperature, and surface wind speed because the surface specific humidity depends on the local air temperature and saturated specific humidity is a function of SST. We attempt to assess quantitatively which parameters–that is, SST, surface air temperature, and wind speed–contribute in determining THF, by applying a simple experiment; two types of datasets are prepared for bulk parameters. One is raw daily data and the other is daily climatological data. Then, we reveal the role of SST in determining the THF over the eKOC. - (ii) Understanding of SST variations in the eKOC
We expect that the Kuroshio bifurcation (see Fig. 2) has important role in determining the SST in the eKOC. We investigate changes in intensity and location of the Kuroshio bifurcation, by using the satellite-derived altimetry dataset. By performing a composite analysis based on states of Kuroshio bifurcation (strengthening/weakening periods or northward/southward location periods), we explore influences of the Kuroshio Bifurcation to oceanic conditions (temperature, salinity, and density) using the Argo float. Additionally, by using the hindcast model outputs, we quantitatively assess a contribution of the Kuroshio bifurcation for the determination of SST in the eKOC.
References
Sugimoto, S., and K. Hanawa, 2011: Roles of SST Anomalies on the Wintertime Turbulent Heat Fluxes in the Kuroshio–Oyashio Confluence Region: Influences of Warm Eddies Detached from the Kuroshio Extension. Journal of Climate, 24, 6551–6561.
