Seasonal variability of alongshore winds and sea surface temperature fronts in Eastern Boundary Current Systems

Abstract

Seven years of satellite observations (2003)(2004)(2005)(2006)(2007)(2008)(2009)) are used to describe variability in sea surface temperature (SST) fronts and in the alongshore component of ocean winds, and to investigate their relations in four Eastern Boundary Current Systems (EBCS). The general patterns of SST frontal activity are remarkably similar in all EBCS, with high frontal probabilities along the coast decreasing with distance from the coastline. Results from empirical orthogonal function decompositions reveal that the seasonal evolution of SST fronts and wind stress are significantly correlated, with intensified upwelling favorable winds associated with an increase in frontal probabilities. An offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in EBCS. In all regions, the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes. The width of the region of high frontal activity is relatively broader in the California and Benguela Current Systems, and narrower in the Canary and Humboldt Current Systems. The width of the band of high frontal activity may be influenced by multiple factors, including wind forcing, flow topography interactions, and mesoscale dynamics. While seasonal variability in frontal activity in the California Current System acts to reinforce or weaken the average pattern, they are substantially different in the Canary Current System, where there is little overlap in the areas characterized by persistent and seasonally varying front activity.

Changes in the partial pressure of carbon dioxide in the Mauritanian–Cap Vert upwelling region between 2005 and 2012

“…But during the Chlorophyll a maximum (late spring and summer), most of the CO 2 was consumed and/or exported and, therefore, the rate was strongly reduced. (Wang et al, 2015). The different changes in temperature in the coastal slope and offshore waters are related to the different origins of the waters upwelled from depths of about 100 m to the surface (Mittelstaedt, 1983) that spread off the coastal area.…”

Coastal Upwelling Front Detection off Central Chile (36.5–37°S) and Spatio-Temporal Variability of Frontal Characteristics

“…In those cases, T o f f shore − T nearshore can be approximated by the sum of DT and the SST differences across all these secondary fronts. The occurrence of such secondary SST gradients is enhanced during summer [34], increasing the difference between DT and T o f f shore − T nearshore . Between March and November, the front is also broadened (Figure 8b).…”

“…The algorithm has proved to be robust off Central Chile, where it was able to distinguish the main upwelling front from this strong mesoscale field. Mesoscale SST gradients in this region are particularly strong [34]. Thus, the method can all the more be applied to SST fields presenting less strong SST mesoscale field such as other areas, time-averaged SST maps, or lower resolution products.…”

“…The propagation of coastal-trapped waves (CTW) also plays a role in the SST variability [24,28], in particular during El Niño Southern Oscillation (ENSO) events [29,30]. The imprint of CTWs is strong in the Northern HCS, but off Central Chile (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) • S) their amplitude is largely attenuated so that the SST can be inferred from a one-dimensional model forced by the local wind stress and solar heating [24]. The region off Central-South Chile (35)(36)(37)(38)(39)(40) • S) is characterized by a strong seasonality in the coastal wind stress and the wind stress curl, with upwelling-favorable wind conditions from September to April (e.g., [13,31]).…”

“…Studying a few cases in this area, Letelier et al [7] suggested that the upwelling front position corresponds to that of the coastal jet meander. Just north of Point Lavapie, relative high mean frontal probabilities and an enhancement of frontal activity over the shelf and up to 200 km offshore have been observed [34]. In this area, the characteristics of the main upwelling front and their frequency of variability remain poorly described.…”