Ocean state indicators from MyOcean altimeter products

Abstract

The Sea Level Thematic Assembly Center from the MyOcean project provides observations of the ocean dynamic topography from altimeter measurements. Three specific indicators have been developed, based on altimeter data only, in order to monitor the ocean state. The first ocean indicator observes the positive and negative phases of the ENSO events in the Tropical Pacific, the El Niño/La Niña events since 1992. The second ocean indicator checks the contracted or extended state of the Kuroshio Extension. The last ocean indicator is dedicated to the Ionian basin in the Mediterranean Sea and permits to separate "zonal-cyclonic" state (1998–2005 and since 2011 up to now) from the "anticyclonic" state (1993–1996) usually discussed in the literature. In addition it allows identifying a third state in which both the anticyclonic circulation around the northern part of the basin and the strong zonal Mid-Ionian jet co-exist (2008–2010). Besides providing useful indices to monitor the ocean state, these indicators are a new tool to assess the long-term quality of the SLTAC products

A process study of the Adriatic‐Ionian System baroclinic dynamics

“…This spatial pattern reflects the wind curl spatial variability as pointed out in the previous section (see also the next section for the vorticity budget analysis). In the case of OPWIND (Figures b, d, and f) the period 1993–1997 (Figure 4b) is characterized by a permanent positive SSH anomaly (anticyclonic circulation) occupying the Ionian [ Borzelli et al ., ; Gacic et al ., , Bessières et al ., ] whereas in the 1998–2005 (Figure d) the Ionian Sea is mostly filled by the negative SSH anomaly (cyclonic circulation) with a positive anomaly limited to the southern basin and Sicily Strait [ Borzelli et al ., ; Gacic et al ., ; Bessières et al ., ]. Finally, the period 2006–2008 (Figure f) in OPWIND is characterized by a new positive anomaly (corresponding to an anticyclonic pattern) occupying the whole basin [ Gacic et al ., ; Theocharis et al ., ].…”

“…Our experiments reproduced the different reversals observed in the Ionian Sea in 1997 and 2006 [ Borzelli et al ., ; Gacic et al ., ; Bessières et al ., ; Theocharis et al ., ]. In this framework the wind plays a primary role in the vorticity and kinetic energy budget of the basin [ Korres et al ., ; Demirov and Pinardi , ; Molchard et al ., ] but it is not the primary player driving the variability observed [ Gacic et al ., ; Theocharis et al ., ].…”

“…The variability of the thermohaline circulation in the EMED was further argued as a consequence of the variability in the vorticity of the Northern Ionian Gyre (NIG) which has been observed periodically to reverse from anticyclonic to cyclonic and viceversa [ Gacic et al ., ; Schroeder et al ., ; Bessières et al ., ]. This decadal oscillation affecting the spreading of the AW eastward and LIW westward in the AISys, is able to influence the salinity in the Eastern Basin [ Gacic et al ., ], in the Sicily channel [ Gacic et al ., ] and the advection of nutrients and salt in the Adriatic Sea [ Civitarese et al ., ; Gacic et al ., ].…”

“…This mechanism suggests that internal processes are able to sustain the variability of the circulation in the Ionian independently from external forcings such as wind [ Gacic et al ., ] . After a first transition from an anticyclonic to a cyclonic mode observed during 1997 [ Borzelli et al ., ] altimetric maps have shown a new anticyclonic mode starting in 2006 [ Gacic et al ., ; Bessières et al ., ]. The cyclonic mode started in 2011 and unexpectedly ended in 2012 when a new reversal to anticyclonic conditions was observed [ Gacic et al ., ].…”

Comparison of high resolution hydrodynamic model outputs with in-situ Argo profiles in the Ionian Sea

“…The anticyclonic mode dominated during 2008-2010 period, while a reversion to cyclonic mode occurred in 2011 (Bessières et al, 2013;Gačić et al, 2014). Nevertheless a new anti-cyclonic reversion occurred during 2012 that was associated with the extreme winter conditions in the Adriatic during this year.…”