Location of Argo profiles (red triangles) during 2004-2012 and of XBT profiles along PX30 on 2010.
Even though Argo accumulates many profiles in WBC regions, High Density XBT transects (HRX) obtain observations at much higher spatial resolution along selected lines. Also, the sampling along HRX extends farther shoreward than Argo (in strong EAC shear).
Gray line - number of XBT profiles along PX30 during 1991-2012. Black line - number of XBT profiles along PX30 during the Argo period (2004-2012). Red line - number of Argo profiles during 2004-2012 within 1.5 latitudinal degrees from PX30.
Between the shelf break and the offshore edge of the EAC at 155°E, there are about 700 XBT profiles (from 34 transects, 2004-2012), compared with about 100 Argo profiles and trajectories.
Transports across PX30
Cumulative transport between 0-800 m from Argo (Red line) and XBTs (Black line). The reference level at 800 m is used for this computation.
For estimating geostrophic shear across the given track in the upper 800 m, HRX transects have less random error and sampling/coverage bias (from along-current averaging and near-shore data) than Argo.
Adjusted cumulative transport from XBTs.
Then, (not shown) altimetric sea surface height is used (i) to adjust deep Argo shear (800-2000 m) to the same mean time period as HRX, (ii) to estimate time variability in transport (correct for temporal aliasing of HRX data) and reduce the error of the mean transport.