April 2022 : Update of the Kuroshio Extension Index
The Kuroshio Extension is characterized by a strong variability. This variability results in two rather different states of the Kuroshio Extension: an "elongated state" corresponding to a narrow strong steady jet with two clear meanders vs a "contracted state" in which the jet is weaker and more unsteady, spreading on a wider latitudinal band. Between these two main states, the Kuroshio Extension has many neutral states of transition and presents either progressively weakening or strengthening trends. An indicator based on the variability of the high-frequency eddy kinetic energy (EKE) in a specific box well checks these Kuroshio Extension states.
In April 2022, the processing of the Kuroshio Extension Index has been updated to take into account a longer period to estimate the mean high-frequency EKE within the 142-149°E and 32-37°N box, and uses the new version of the altimetry maps (DUACS DT2021, see https://catalogue.marine.copernicus.eu/documents/QUID/CMEMS-SL-QUID-008-032-068.pdf).
The changes are summarized in the table below:
| Previous version | April 2022 version | |
|---|---|---|
| Duacs reprocessing | DT-2018 | DT-2021 |
| Temporal period for the mean | 1993-2013 | 1993-2020 |
Impact on the Kuroshio Extension Index :
The figure below shows the impact on the Kuroshio Extension index timeseries. The green curve represents the previous version and the blue curve the April 2022 version. The differences are small and do not modify strongly the “contracted state” (above the dashed orange dashed line) and the “elongated state” (below the dashed light blue line) temporal periods.
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