In this study, high resolution coupled and uncoupled regional atmospheric (WRF) and oceanic (ROMS) simulations for the Californian Current System are used to assess how air-sea interactions affect upwelling, atmosphere variability and primary production at different time scale. The simulations are done over the 1995-2009 time period including the 1997-1998 El Niño event. As a first step, the CORE bulk formulae has been implemented and tested in uncoupled ROMS simulations using different atmospheric products. Main results show its ability in estimating realistically both momentum and turbulent heat fluxes. However, these first simulations highlight that, due to a poor representation of both solar radiations and coastal surface wind, global product are not reliable to force such oceanic simulations. We then show that our uncoupled and coupled longterm simulations are realistic and contain a wide range of scales from daily to interannual. By coupling Ocean to Atmosphere, the mixed-layer heat balance is impacted through a combination of different solar radiations, turbulent heat fluxes and vertical mixing. The upwelling intensity and structure are also impacted leading to a different biogeochemical response.