Coupled Ocean/Atmosphere regional simulation of Coastal Jet off Central Chile: A case study for the October 2000 event

Renault L., Dewitte B., Echevin V., Illig S., Vizoso G., Tintore J.


The cool waters off central Chile (26°S-36°S) are principally maintained by coastal upwelling, which is driven by persistent low-level along-shore southerly winds. Satellite data, marine reports, and coastal in situ observations off central Chile indicate that those along-shore winds intensify at intraseasonal timescale leading to Coastal Jets (CJs). The southerly jet events off central Chile occur year round but are more frequent during the upwelling season in summer (over 60% of the time). The jet is characterized by an elongated maximum of surface wind speed (10m s-1) with its axis at about 150 km off the coast and a cross-shore scale of about 500 km. The available observations (essentially remote sensing) show the CJ activity is seasonally phase locked with SST, with a peak season in August–October. They suggests that the statistically dominant forcing mechanisms of the SST cooling during CJ event is a combination of seaward advection of temperature resulting from Ekman transport, air-sea heat exchange, and Ekman-driven coastal divergence.

In this work - using high-resolution ocean (ROMS) and atmosphere (WRF) regional model - focus is given on the October 2000 Coastal Jet event (Garreaud et al., 2005, Renault et al., 2009). Our aim is to document the forcing mechanisms of CJ events. After validating the model variability from the available observations, the main statistical 3D characteristics of the oceanic response to a CJ event are analysed. In particular, taking advantage of the model resolution, an complete heat budget within the mixing layer during this CJ event is estimated, both in the coastal area and in the offshore area (in the vicinity of the CJ core). The results show that coastal upwelling is the main contributor of the observed cooling in the coastal area, whereas, in the neighbourhood CJ core, the ocean temperature cooling is a combination of advection, heat fluxes and mixing layer entrainment.