Air‐sea interaction at the Southern Brazilian Continental Shelf: In situ observations

Abstract

The influence of the cross‐shelf oceanographic front occurring between the Brazil Current (BC) and the Brazilian Coastal Current (BCC) on the local Marine Atmospheric Boundary Layer (MABL) is investigated here. This front is typical of wintertime in the Southern Brazilian Continental Shelf (SBCS) and this is the first time that its effects are investigated over the above MABL. Here we analyze variability, vertical structure, and stability of MABL as well as heat fluxes at air‐sea interface, across five oceanographic transects in the SBCS made during a winter 2012 cruise. Local thermal gradients associated with mixing between distinct water masses, play an essential role on MABL modulation and stability. Although weaker when compared with other frontal regions, the cross‐shelf thermal gradients reproduce exactly what is expected for open ocean regions: Stronger (weaker) winds, lower (higher) sea level pressure, and a more unstable (stable) MABL are found over the warm (cold) side of the oceanographic front between the BC (warm) and coastal (cold) waters. Our findings strongly support the coexistence of both known MABL modulation mechanisms: the static and hydrostatic MABL stability. This is the first time that these modulation mechanisms are documented for this region. Turbulent fluxes were found to be markedly dependent on the cross‐shelf SST gradients resulting in differences of up to 100 W.m−2 especially in the southernmost region where the gradients were more intense.

Regional modeling of the water masses and circulation annual variability at the Southern Brazilian Continental Shelf

“…At this period, a very recent paper by Pezzi et al . [] reported the importance of the typical across‐shore SST gradients present in the study region in winter for the modulation of the marine atmospheric boundary layer and, consequently, for the weather of southern Brazil. This paper describes the major processes responsible for sustaining these across‐shore SST gradients in wintertime as well as their annual variability.…”

“…Future work will be directed to implement and validate a regional coupled ocean‐atmosphere model for the SBCS to better describe the dynamical processes controlling the air‐sea coupling processes recently described by Pezzi et al . []. That can largely improve our knowledge on the coastal ocean's role on modulating the weather of southern Brazil.…”

“…The paper focuses in the year of 2012 when the first research cruise was performed during winter with the objective of studying the ocean‐atmosphere coupling mechanisms in the SBCS region, as recently reported by Pezzi et al . []. These authors attested the importance of the across‐shelf SST gradients occurring in our study area to modulate the marine atmospheric boundary layer (MABL) immediately above, consequently affecting the weather of the coastal regions off southern Brazil.…”

“…This paper makes use of ROMS to present new evidence on how the coastal water masses, associated fronts and circulation vary throughout the year. These variables and processes sustain the local SST gradients recently proved to be as important to the atmospheric circulation and weather [ Pezzi et al ., ] as they are to the local ecosystem.…”

Long‐Term Monitoring of the Brazil Current Transport at 22°S From XBT and Altimetry Data: Seasonal, Interannual, and Extreme Variability

“…Near Cabo Frio (~23°S, 42°W), the BC is characterized by intense meandering and occasional eddy shedding (da Silveira et al, ; Pilo et al, ), and these features of the BC dynamics have been associated to modulations in coastal upwelling (e.g., Calado et al, ; Campos et al, ). The Cabo Frio upwelling, which is stronger during the austral summer, creates a strong sea surface temperature (SST) front by bringing cold central waters to the surface, enhancing the local biological productivity (Gonzalez‐Rodriguez et al, ), decreasing the coastal sea level via Ekman divergence, and forcing the marine boundary layer and surface turbulent fluxes, with potential impact on the weather patterns in the Southeast South America (e.g., Chelton et al, ; Pezzi et al, ; Ribeiro et al, ). Evans and Signorini () described the BC near 23°S as a 400‐ to 500‐m‐deep surface boundary current with a southward volume transport offshore of the shelf break of approximately 6 Sv (1 Sv = 10 6 m 3 /s).…”