Re: One front or two fronts?

Subject:

Comments:
: Dear Bo, : Thank you for your helpful comments! : Regarding the 3 time series, although the signal of the Northern Branch in the SSH field is weak, we could determined its location and that of the Kuroshio Extension by using indicative isotherms. From the model we obtained an upper layer thickness defined to go from the sea surface to the depth of the 9°C isotherm. The location of the 9°C isotherm at 500 m depth, associated with the KE front and validated with hydrographic data at 144°E, was used as indicative of the KE at the first crest; and the location of the 9°C isotherm at 250 m depth, associated with the Kuroshio Bifurcation front and validated with hydrographic data at 165°E, was used as indicative of the Northern Branch. The bifurcation longitude was determined from the distance between both indicative isotherms, assuming that they are associated with the KE front west of the bifurcation, and with two different fronts (KEF and KBF) east of the bifurcation. : The transport values shown in our study are mean values for the total period of the "upper layer transport" (from the sea surface to the depth of 9°C), not absolute transports. Peaks of over 60 SV in the first crest agrees with those obtained from observations for the same layer. : Thank you again! : Susana. : : Susana, : : I read your poster with great interest. I am particularly intrigued : : by your 3 time series, indicating that when the KE's 1st crest : : moves northward, the KE's volume transport decreases and its bifurcation : : latitude shifts eastward. : : Lack of subsurface in-situ measurements, I assume that this conclusion : : of yours is based on the T/P data analysis. Although the double frontal : : structure of the KE is discernible in some T(y,z) observations downstream : : of the Shatsky Rise, my experience with the T/P (and the Geosat ERM) data : : is that this double-front structure is very difficult to detect in the : : SSH measurements. (In your response to Randy's comment, you seem to : : agree with this point.) Given this, I wonder how you have determined the : : the time series for the northern branch and the bifurcation latitude? : : Both Randy and Bruce raised the issue on whether the Oyashio variability : : can affect the KE path signals. My thought on this is close to yours, namely, : : at least in the region between 140E and the Shatsky Rise (~160E), the KE's : : inertia and the nearly right-angled coastal geometry of Japan cause a : : "buffer" zone (the so-called Mixed Water Region) in between the eastward : : flowing KE and Oyashio. As such, the upstream KE path variability is : : dictated more likely by the Kuroshio state south of Japan (via inflow : : condition), its interaction with the Izu Ridge, and the presence of the : : recirculation gyre (through nonlinearity). : : With regard to the transport values, I am a little surprised that the : : numbers shown in your map are so small (e.g., 35Sv for the KE just east : : of Japan). A recent WOCE survey with CTD, LADCP, and ship-board ADCP : : showed that the eastward KE transport at this location reaches 130Sv : : (see Fig.6 of Wijffels et al., JGR, 1998, 12,985-). The inflated : : eastward transport of the KE is due to the presence of the southern : : recirculation gyre. Interestingly, the survey by Wijjfels et al. shows : : that the recirculation has a transport of ~80 Sv, rendering the net : : eastward transport of the KE to 50 Sv, a value very close to the : : interior Sverdrup transport. : : My final comment is that because the KE and its recirculation gyre : : have very different vertical structures, the 1.5-layer approach may be : : difficult to distinguish the volume transport changes due to the KE : : itself or its recirculation gyre. : : Cheers, Bo