Contribution d'Angélique MELET, Jacques VERRON & Jean-Michel BRANKART:

Glider assimilation in the Solomon sea

In the southwest Pacific, the western boundary currents (WBC) connect the tropics to the equator at thermocline level. Therefore, they may impact the equatorial Pacific heat and transport budgets and play a role in the climate system. Those WBC transit through the Solomon Sea before reaching the equator. As available observations of the region are sparse, modeling provides a useful complementary tool to describe the oceanic circulation is this region, which shows high variability as shown by altimetric and modeling analysis. An integrated view of the circulation combining numerical simulation and available observations, through data assimilation, is probably the way to provide a realistic description of the Solomon Sea. Glider monitoring of the Solomon Sea circulation has been operated since 2007. Those autonomous underwater vehicles provide high temporal and along-trajectory resolution temperature and salinity data down to about 600 m, which are of interest for the control of meso-scale variability of the Solomon Sea WBC. This is the motivation of this work which focuses on the control of the Solomon Sea WBC, the New Guinea Coastal Undercurrent (NGCU), through assimilation of glider and other observational data. At this stage, the objective is rather to assess the capability of existing or expected observing system than to perform realistic data assimilation experiments per se. An observing system simulation experiments (OSSE) strategy is implemented in a twin experiment context to study the ability of glider observations to constrain the NGCU. From a methodological point of view, we performed original data assimilation in a multigrid model through a local reduced order analysis, based on a sequential scheme derived from the SEEK filter. Observations are located in a 1/12 model of the Solomon Sea which is interactively nested in a 1/4 southwest Pacific model, itself embedded through open boundary conditions in a global 1/4 OGCM.

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