Impact of atmospheric coastal jet off central Chile on sea surface temperature from satellite observations (2000-2007)

摘要

The coast of central Chile is characterized by intermittent low-level along-shore southerly wind periods, called coastal jets (CJs). In this study, we take advantage of longterm satellite data to document the CJs characteristics over 2000-2007 and investigate its impact on upwelling. The CJ structure has a core some 100 km from the shore and a cross-shore scale of -160 km, and it usually lasts for several days (3-10). Its period of occurrence ranges from weekly to a few months. On the basis of covariance analyses between wind stress and sea surface temperature (SST) anomalies, it is found that CJ activity is seasonally phase locked with SST, with a peak season in August—October. 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. However, case studies of two events suggest a significant sensitivity of the dominant upwelling forcing mechanisms to the background conditions. For instance, the upward Ekman pumping associated with cyclonic wind stress curl is enhanced for the event with the CJ located more to the south. Although there are limitations associated with both the formulation of the heat budget and the data sets, the results illustrate the complexity of the upwelling forcing mechanisms in this region and the need for realistic high-resolution forcing fluxes. A CJ activity index is also proposed that takes into account the coastal upwelling variability, which can be used for teleconnection studies.