Modeling interannual and decadal variability in the Humboldt Current upwelling system Combes V., E. Di Lorenzo, F. Gomez, S. Hormazabal, T. P. Strub and D. Putrasahan The Humboldt Current System (HCS) is the one of the world’s most productive regions in fish landings, providing 18 to 20% of the world marine catches despite covering less than 1% of the world’s ocean surface. This high productivity results principally from the upwelling of nutrient-rich water in the photic zone. This study investigates the HCS variability using a free-surface, hydrostatic, eddy resolving primitive equation model combined with a passive tracer advection-diffusion equation. The upwelling variability, important in understanding the ecosystem dynamics, is examined using a model passive tracer, continuously released at the coast in the subsurface between 150 and 250 m depth. The concentration of that tracer observed at the surface can therefore be considered as an index of coastal upwelling. Different model experiments are conducted to explore the sensitivity of the HCS upwelling to different air-sea fluxes of momentum and atmospheric and oceanic teleconnections to ENSO. On average, we find that the model runs forced by ECMWF and QSCAT wind stress compare better with observations than the experiment forced by NCEP wind stress, with strong upwelling off Peru (5°S-16°S) and central Chile (27°S-34°S) and significantly weaker upwelling in the North Chile Region (18°S-24°S), consistent with the strength of coastal upwelling-favorable winds. Temporal variability is nevertheless well reproduced by NCEP, when comparing model and in situ coastal sea surface height data. There is evidence, in this region, that both changes in surface wind and coastally trapped Kelvin waves controlled the variability of the coastal upwelling. The effect of ocean remote forcing, assessed by comparing the output of two model simulations which does and does not include the presence of waves in their boundaries. The passive tracer approach indicates that, off the coast of Peru, the Southern Oscillation strongly modulates the strength of coastal upwelling principally due to the propagation of downwelling equatorial Kelvin waves (particularly strong during El Niño years) rather than changes in local wind stress. Off central Chile, we find that the first mode of coastal upwelling variability is also strongly correlated with the Southern Oscillation with a decadal variability signal that seems to respond to the second mode of sea level pressure in this region. Our results indicate that the central Chile region is also very sensitive to Kelvin wave generated at the equator, reducing for example considerably the upwelling during strong El Niño events, therefore impacting the ecosystem variability. COMBES_PCCS_TABLE_RUN COMBES_PCCS_UPWELLING