Under SAGE project (Sub-Arctic Gyre Experiment), an intensive observation line along the TOPEX/POSEIDON (T/P) orbit 060 had been set to estimate the Oyashio transport. We named this line as OICE (Oyashio Intensive observation line off-Cape Erimo). On the OICE we had been repeating the hydrographic observations and maintaining the mooring systems.
Before comparing the T/P derived sea surface height anomaly (SSHA) with velocity and transport in the Oyashio region, the characteristics of SSHA in that region was invesigated. The de-correlation scale of SSHA was estimated about 80-110 km in the Oyashio regioin. The SSHA also contains horizontal small scale noises and an Gaussian filter was used to eliminate the noises. In the comparison of the SSHA difference across two selected points and subsurface velocity measured by moored ADCP, the highest correlation (0.92) appeared when the smoothing scale is 30km and the horizontal distance is shortened as possible.
For the transport in the Oyashio region, geostrophic transport between 39Z30′N and 42ZN was compared with SSHA difference across the same two points. In this case the highest correlation (0.79, 0.82 and 0.93) is performed when the smoothing scale is 38, 6 and 10 km in 1000, 2000 and 3000 db referenced cases, respectively. The Oyashio transport time series was derive from T/P SSHA data and showed smaller value than that estimated from the Sverdrup balance in 1994-1996 and larger value than it in 1997-2000. This difference was consistent with the baloclinic repsponce suggested by Qiu (2002) |
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