A B S T R A C TThis paper provides a description of the wave climate off the Brazilian coast based on an eleven-year time series (Jan/1997-Dec/2007) obtained from the NWW3 operational model hindcast reanalysis. Information about wave climate in Brazilian waters is very scarce and mainly based on occasional short-term observations, the present analysis being the first covering such temporal and spatial scales. To define the wave climate, six sectors were defined and analyzed along the Brazilian shelf-break: South (W1), Southeast (W2), Central (W3), East (W4), Northeast (W5) and North (W6). W1, W2 and W3 wave regimes are determined by the South Atlantic High (SAH) and the passage of synoptic cold fronts; W4, W5 and W6 are controlled by the Intertropical Convergence Zone (ITCZ) and its meridional oscillation. The most energetic waves are from the S, generated by the strong winds associated to the passage of cold fronts, which mainly affect the southern region. Wave power presents a decrease in energy levels from south to north, with its annual variation showing that the winter months are the most energetic in W1 to W4, while in W5 and W6 the most energetic conditions occur during the austral summer. The information presented here provides boundary conditions for studies related to coastal processes, fundamental for a better understanding of the Brazilian coastal zone. R E S U M OO presente trabalho apresenta o clima de ondas da região ao largo da costa brasileira com base em uma série temporal de onze anos (Jan/1997-Dez/2007) obtida através de dados de reanálise do modelo operacional NWW3. Informações sobre o regime de ondas no Brasil são escassas e baseadas em observações ocasionais de curto período, sendo a presente análise inédita na escala espaço-temporal apresentada. Para a definição do clima de ondas foram definidos e analisados seis setores ao longo da quebra da plataforma continental brasileira: Sul (W1), Sudeste (W2), Central (W3), Leste (W4), Nordeste (W5) e Norte (W6). W1, W2 e W3 possuem os regimes de ondas controlados pela Alta Subtropical do Atlântico Sul (ASAS) e pela passagem de frentes frias sinóticas; W4, W5 e W6 são controlados pela Zona de Convergência Intertropical (ZCIT) e sua oscilação meridional. As ondas mais energéticas são de S, geradas por ventos intensos associados à passagem de frentes frias, afetando principalmente a região sul e sudeste do país. A energia das ondas apresenta um decréscimo de sul para norte, com a sua variação anual mostrando que o período de inverno as ondas são mais energéticas nos setores W1 a W4, enquanto que nos setores W5 e W6 as condições mais energéticas ocorrem nos meses de verão do hemisfério sul. As informações aqui apresentadas fornecem condições de contorno para diferentes estudos relacionados a processos costeiros, fundamentais para a melhor compreensão da zona costeira do Brasil.

[1] Several mechanisms can drive vertical velocities in the coastal ocean, including windforcing and through gradients in the vorticity field generated by flow-topography interactions. A two-layer, steady, wind-driven, analytical model is applied to the major upwelling systems of Brazil: Cabo Frio (CF) and Cabo de Santa Marta (CSM) regions. Comparisons are made between the relative roles of wind and flow-topography interaction in inducing upwelling over these regions. Ekman pumping is the weakest mechanism over the shelf, but does influence the along-shelf temperature in the CF area. Away from coastline irregularities, wind-driven upwelling (Ekman transport) dominates over all mechanisms. However, in the vicinity of capes and coastal features, topographically driven upwelling plays a significant role, and its transports may vary from 43% to 94% of winddriven upwelling. Upstream of capes, topographically driven vertical motions are downwelling favorable and act against the wind-driven coastal upwelling, while downstream of capes, they are upwelling favorable, where all mechanisms add up to create strong upwelling. Peaks in total upwelling in the CF region are about twice as large as those in the CSM area because the CF region has stronger winds and larger coastline perturbations than in the CSM region. Observed sea surface temperatures (SST) agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast. Results suggest that on larger scales, the SST variability along the coast is mainly controlled by wind-driven upwelling, while upwelling due to flowtopography interaction is responsible for the smaller scale SST variability.

From 11 April to 11 June 2018 a new type of ocean observing platform, the Saildrone surface vehicle, collected data on a round-trip, 60-day cruise from San Francisco Bay, down the U.S. and Mexican coast to Guadalupe Island. The cruise track was selected to optimize the science team’s validation and science objectives. The validation objectives include establishing the accuracy of these new measurements. The scientific objectives include validation of satellite-derived fluxes, sea surface temperatures, and wind vectors and studies of upwelling dynamics, river plumes, air–sea interactions including frontal regions, and diurnal warming regions. On this deployment, the Saildrone carried 16 atmospheric and oceanographic sensors. Future planned cruises (with open data policies) are focused on improving our understanding of air–sea fluxes in the Arctic Ocean and around North Brazil Current rings.

During fall/winter off the Oregon coast, oceanographic surveys are relatively scarce because of rough weather conditions. This challenge has been overcome by the use of autonomous underwater gliders deployed along the Newport hydrographic line (NH-Line) nearly continuously since 2006. The discharge from the coastal rivers between northern California and the NH-Line reach several thousands of cubic meters per second, and the peaks are comparable to the discharge from the Columbia River. This freshwater input creates cross-shelf density gradients that together with the wind forcing and the large-scale Davidson Current results in strong northward velocities over the shelf. A persistent coastal current during fall/winter, which the authors call the Oregon Coastal Current (OCC), has been revealed by the glider dataset. Based on a two-layer model, the dominant forcing mechanism of the OCC is buoyancy, followed by the Davidson Current and then the wind stress, accounting for 61% (±22.6%), 26% (±18.6%), and 13% (±11.7%) of the alongshore transports, respectively. The OCC average velocities vary from 0.1 to over 0.5 m s−1, and transports are on average 0.08 (±0.07) Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), with the maximum observed value of 0.49 Sv, comparable to the summertime upwelling jet off the Oregon coast. The OCC is a surface-trapped coastal current, and its geometry is highly affected by the wind stress, consistent with Ekman dynamics. The wind stress has an overall small direct contribution to the alongshore transport; however, it plays a primary role in modifying the OCC structure. The OCC is a persistent, key component of the fall/winter shelf dynamics and influences the ocean biogeochemistry off the Oregon coast.

Prolonged events of anomalously warm sea water temperature, or marine heatwaves (MHWs), have major detrimental effects to marine ecosystems and the world's economy. While frequency, duration and intensity of MHWs have been observed to increase in the global oceans, little is known about their potential occurrence and variability in estuarine systems due to limited data in these environments. In the present study we analyzed a novel data set with over three decades of continuous in situ temperature records to investigate MHWs in the largest and most productive estuary in the US: the Chesapeake Bay. MHWs occurred on average twice per year and lasted 11 days, resulting in 22 MHW days per year in the bay. Average intensities of MHWs were 3°C, with maximum peaks varying between 6 and 8°C, and yearly cumulative intensities of 72°C × days on average. Large co-occurrence of MHW events was observed between different regions of the bay (50–65%), and also between Chesapeake Bay and the Mid-Atlantic Bight (40–50%). These large co-occurrences, with relatively short lags (2–5 days), suggest that coherent large-scale air-sea heat flux is the dominant driver of MHWs in this region. MHWs were also linked to large-scale climate modes of variability: enhancement of MHW days in the Upper Bay were associated with the positive phase of Niño 1+2, while enhancement and suppression of MHW days in both the Mid and Lower Bay were associated with positive and negative phases of North Atlantic Oscillation, respectively. Finally, as a result of long-term warming of the Chesapeake Bay, significant trends were detected for MHW frequency, MHW days and yearly cumulative intensity. If these trends persist, by the end of the century the Chesapeake Bay will reach a semi-permanent MHW state, when extreme temperatures will be present over half of the year, and thus could have devastating impacts to the bay ecosystem, exacerbating eutrophication, increasing the severity of hypoxic events, killing benthic communities, causing shifts in species composition and decline in important commercial fishery species. Improving our basic understanding of MHWs in estuarine regions is necessary for their future predictability and to guide management decisions in these valuable environments.