Low-level coastal jet off central Chile: Climatology, dynamics, and associated cloud/SST properties

We use 4 year of QuikScat satellite-derived winds over the ocean to build a basic climatology of the low-level wind regime off the coast of north and central Chile. The main feature in this climatology is a region of maximum southerly winds between latitudes 30o and 37o S, which is due to the frequent occurrence of coastal jet events. Analysis of in-situ data and model results of a well-defined jet event allows for a preliminary characterization of the jet's three-dimensional structure.

This coastal jet is characterized by a small diurnal cycle and large synoptic-scale variability. Typically, the jet core is about 150 km off the coast and resides at the top of the MBL / base of the inversion layer. Numerical model results show that the jet is in a semi-geostrophic balance, in which only the cross-shore force balance is geostrophic. The coastal jet is a main factor controlling the turbulent and cloudy structure of the coastal MBL.

The surface stress exerted by the southerly winds foster the upwelling of cold, nutrient rich waters, supporting a wealth of fishery resources. Coastal upwelling is significantly enhanced during coastal jet events. Furthermore, correlation between Quikscat winds and GOES-derived cloud fractions show a tendency to have a coastal jet under clear skies, in contrast with an increase in low-level cloudiness downstream of the jet.

Surface meteorological stations at the coast show the hallmark of the coastal jet in a near-meridional wind direction sector having the largest wind speeds. While the afternoon flow near the coast is highly correlated to the intensity of the flow offshore (as derived from Quikscat), the nocturnal flow regime at the coast is much weaker and mostly uncorrelated with the flow farther offshore.