Surface Thermal Structure and Variability of Upwelling Shadows in the Gulf of Arauco, Chile

Abstract

Enhanced coastal upwelling usually occurs near capes (e.g., Castelao & Barth, 2007), due to vorticity effects along with the acceleration of winds and currents (Largier, 2020). Moreover, the wind shadows and upwelling circulation around capes can also generate upwelling shadows on the side protected from the upwelling jet and alongshore wind. An upwelling shadow has been defined as "a localized region of an active coastal upwelling system within which upwelling is reduced, and a coherent pattern of anomalously high

Upwelling Shadows Driven by the Low‐Level Jet Along the Subtropical West Coast of South America: Gulf of Arauco, Chile

“…The SST pattern was also coherent with the one observed in a previous work (Wong et al, 2021), where the reported mean thermal difference between GA and PL was about 1 °C. The wind intensification in PL and the stronger SST gradient between PL and GA, observed for US days, also agree with the US conditions described by Wong et al (2021). The analysis of composites and the study of two cases allows us to connect well-studied synoptic-scale atmospheric phenomena with the occurrence of US events in the GA.…”

“…US days inside GA were defined using an index developed by Wong et al. (2021). An US event was set as three or more consecutive US days, finding 40 events during the austral summer from January 2011 to September 2019.…”

“…An USI was defined by Wong et al. (2021) and is calculated as follows: $$$USI=\left({T}_{GA}-{T}_{PL}\right)\ast {m}_{f}$$$ where T GA = mean SST in the GA (red box in Figure 1). T PL = mean SST west of SMI (blue box in Figure 1).…”

“…In general, equator-facing bays along the Chilean upwelling region, such as Tongoy Bay (∼30°S) and Mejillones Bay (∼23°S), seem to play a similar role (Castilla et al, 2002;Marín et al, 2001Marín et al, , 2003 as the GA (Letelier et al, 2009). Wong et al (2021) constructed an index to identify the US in GA and, through statistical analysis, established the frequency and duration of events and also found that the multiple correlations between US and wind stress curl and solar radiation resulted in a higher percentage (r 2 = 40-80%) for some summer months. Wong et al (2021) also analyzed the response of the US to short and long wind relaxation periods finding a low correlation, which suggests that there are other processes involved in the formation and development of the US inside the GA. Delving into the processes that explain the development of the US in this area is the primary motivation of this work.…”

Seasonal and interannual variability of sea surface temperature around the gulf of the Farallones, California

“…During upwelling events, surface waters in upwelling centers are advected equatorward and alongshore until encountering topographic features that alter surface flow (Graham & Largier, 1996;Woodson et al, 2012;Mazzini and Barth, 2013;Wong et al, 2021). In the lee (equatorward) of topographic features, where wind-forcing is reduced, the upwelling plume may bifurcate, with a portion of the plume continuing equatorward along the coast, and the remaining recirculating poleward.…”