Characterization of westward propagating signals in the South Atlantic from\ud altimeter and radiometer records

Radar altimeter data from TOPEX/Poseidon and Jason-1 and microwave radiometer data from TRMM/TMI are used to investigate the large-scale variability between 10.5°S and 35.5°S in the South Atlantic Ocean. The proposed method for the analysis of the longitude–time diagrams of the cross-correlation between SSH and SST anomalies shows that the variability in mid latitudes is a blend of first-mode baroclinic Rossby waves and propagating mesoscale eddy-like structures. The estimated phase speed of the wave (cp) and propagation speed of the eddies (cv) are similar. In 70% of the cases, the absolute difference between cp and cv is less than 11%. In 40% of the cases this difference is less than 5%. Statistical results indicate that in the case of eddies, as the thermocline deepens the sea surface temperature rises and vice-versa. However, planetary waves show more complex, yet self-consistent results. In lower latitudes (10.5°S–15.5°S), the shallower thermocline and the weak thermal gradients impose a zero phase lag between temperature and height, similar to eddies. Poleward of those latitudes, sea surface temperature and height are in quadrature of phase. This indicates that geostrophic advection of the relatively stronger thermal gradient is performed by Rossby waves

Corrigendum to Characterization of westward propagating signals in the South Atlantic from altimeter and radiometer records ”[Remote Sens. Environ., 134: 367-376]

Radar altimeter data from TOPEX/Poseidon and Jason-1 and microwave radiometer data from TRMM/TMI are used to investigate the large-scale variability between 10.5°S and 35.5°S in the South Atlantic Ocean. The proposed method for the analysis of the longitude–time diagrams of the cross-correlation between SSH and SST anomalies shows that the variability in mid latitudes is a blend of first-mode baroclinic Rossby waves and propagating mesoscale eddy-like structures. The estimated phase speed of the wave (cp) and propagation speed of the eddies (cv) are similar. In 70% of the cases, the absolute difference between cp and cv is less than 11%. In 40% of the cases this difference is less than 5%. Statistical results indicate that in the case of eddies, as the thermocline deepens the sea surface temperature rises and vice-versa. However, planetary waves show more complex, yet self-consistent results. In lower latitudes (10.5°S–15.5°S), the shallower thermocline and the weak thermal gradients impose a zero phase lag between temperature and height, similar to eddies. Poleward of those latitudes, sea surface temperature and height are in quadrature of phase. This indicates that geostrophic advection of the relatively stronger thermal gradient is performed by Rossby wave

Kelps’ long-distance dispersal: role of ecological/oceanographic processes and implications to marine forest conservation

Long-distance dispersal is one of the main drivers structuring the distribution of marine biodiversity. This study reports the first occurrence of Macrocystis pyrifera and Durvillaea antarctica rafts on the southwestern warm temperate coast of the Atlantic Ocean. Our results indicate that an extreme meteo-oceanographic event, characterized by a northward, displacement of cold sub-Antarctic oceanic waters driven by an extratropical cyclone, could account for these unusual occurrences. A niche model based on known current distribution and maximum entropy principle (MAXENT), revealed the availability of suitable habitats at lower latitudes, outside their actual distribution edges. The distributional boundaries, mainly driven by temperature and irradiance, suggest the existence of environmental suitability in warm temperate areas, as well as in the Northern Hemisphere off Atlantic and Asian coasts. These theoretical edges and respective environmental drivers agree with the physiological affinities of both species, supporting the hypothesis that these variables act as limiting factors for their occurrences in tropical or warmer areas. Emerging regions can function as refuges and stepping-stones, providing substrate with adequate habitat conditions for recruitment of propagules, allowing eventual colonization. Long dispersal events reinforce the need for an extensive discussion on selective management of natural dispersion, biological invasions, refuge mapping and conservation initiatives in a transnational perspective.Agência financiadora / Número do subsídio Portuguese Fundacao para a Ciencia e Tecnologia (FCT) SFRH/BPD/111003/2015 PTDC/MAR-EST/6053/2014 Conselho Nacional de Desenvolvimento Cientifico e Tecnológico CNPq 306917/2009-2 Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior CAPES/PNPD 02828/09-0 CAPES/PNADB 2338000071/2010-61 Polito: CNPQ Universal 447109/2014-6 Instituto Nacional de Ciencia e Tecnologia para Mudancas Climaticas (INCT-MC) ProspecMar-Islands-Sustainable prospecting in Ocean Islands: Biodiversity, Chemistry, Ecology and Biotechnology, Boticario Foundation 1051-20152 Rede Coral Vivo, Brazilian Research Network on Global Climate Change REDEALGAS, Brazilian Research Network on Global Climate Change FAPESC-Foundationinfo:eu-repo/semantics/publishedVersio

Global sea surface height trends from altimeter data

Oceanic heat storage variability can be accurately obtained from satellite altimeter measurements of sea surface height anomaly. This study uses the global TOPEX/Jason-1 altimeters time series to estimate the 12-year trend in sea surface height anomaly. One component of the signal variability can be described as basin-scale non-propagating signals that include the seasonal and interannual cycles (e.g. El Niño/La Niña, Indian Ocean Dipole etc.). A second component contains propagating signals characterized as long and short Rossby waves and equatorial Kelvin waves. Meso-scale eddies that do not propagate as waves are treated as the third and last component of the variability. The altimeter signal is decomposed using a chain of 2D finite impulse response filters. For each latitude the zonal mean of the basin-scale signals is calculated, and a smooth spline is is fitted to represent the interannual variability. Furthermore, a linear 12-year trend and its error are estimated from this interannual variability. The propagating and eddy signals are represented by their zonal standard deviation. Again, a smooth spline is is fitted to represent their interannual variability, and a linear fit represents its 12 year trend. A comparison of representative latitudes from the Atlantic, Pacific and Indian Oceans yields provocative results that are focused on the southern hemisphere are summarized next. Basin-scale signals in the equatorial (2.5^oN 2.5^oS) Indian Ocean show no decadal trend; in the Pacific there is a small trend with no statistical significance; in the Atlantic there is a 40 mm increase in height over the studied period. Equatorial Kelvin and Rossby waves in the Pacific and Indian basins show similar amplitudes, indicating an equilibrium between eastward and westward propagating energy. In the Atlantic Rossby waves have almost twice the amplitude of the Kelvin wave and eddy signals. In all basins the amplitude of the wave and eddy signals shows no decadal trend. The northern Indian Ocean shows no decadal trend, while the southern part of the basin shows a trend of approximately 40 mm over 12 years, increasing slightly in higher latitudes. The northern Pacific shows a similar trend between 10.5^oN and 30.5^oN and at 45.5^oN this trend becomes insignificant. Similar observations are made for the southern Pacific except at 45.5^oS, where a very significative trend of approximately 60 mm is observed for the studied period. The north Atlantic shows significative trends of about 30 mm between 10.5^oN and 30.5^oN, while no trend is observed at 45^oN. In the south Atlantic the trends are similar, except for 45^oS, where a very significative trend of approximately 50 mm is observed for the studied period. The relatively high and statistically significant 12 year trend in sea surface height observed at 45^oS suggests that the Southern Ocean, which connects all three basins, is probably experiencing a positive heat flux..Pages: 1329-133

Long-term trend in the oceanic heat storage of the South Atlantic estimated from altimeter and PIRATA data

Changes in the oceanic heat storage (HS) reveal important evidences of climate variability on the ocean heat fluxes. Specifically, long-term variations in the oceanic heat storage is a powerful indicator of climate change as HS represents a balance between the net energy input into the ocean through the surface and the poleward heat fluxes by the ocean currents. Historically, HS has been estimated by integrating the temperature profiles from hydrographic cruises or buoy data. Therefore, the knowledge of its variability is limited by data availability. The use of satellite altimeter data opened up new possibilities to continuously monitor the oceanic HS in a global scale with unprecedented resolution in both space and time. Oceanic heat storage anomalies are estimated from sea surface height anomalies measured from the altimeters TOPEX/Poseidon and Jason 1. To characterize and validate the use of the altimeter based HS in the South Atlantic, we used the data from the Pilot Research Moored Array in the Tropical Atlantic (PIRATA) array. Correlations and rms differences between both time series were calculated to compare the HS estimates. The HS anomaly correlations between the in situ and altimeter data range from 0.56 to 0.86 in the buoys located at the southern part of the array. The rms differences range between 0.37 and 0.47 x 10^7 J m^-2. These results are encouraging and indicate that the altimeter based HS estimates can be used to investigate long term trends in the South Atlantic from 1997 to present. The total HS anomaly signal is decomposed using a series of 2D finite impulse response filters. The signal components are the non-propagating basin-scale and seasonal, westward propagating (Rossby waves), eastward propagating (Kelvin waves), meso-scale eddies, and a small-scale residual. The seasonal and the non-propagating basin-scale components (HST) are in general the dominant signals. The amplitude of the annual cycle of HST varies meridionally from approximately 0.5 x 10^9 J m^-2 at 5.5S to 1.1 x 10^9 J m^-2 at 40.5S. The most striking feature is a decadal trend in HST all over the South Atlantic basin, however the more prominent slopes are found poleward of 40S. The zonally averaged HST component increases by about 1.1 x 10^5 J m^-2 y^-1 within 10o from the equator to 4.7 x 10^5 J m^-2 y^-1 at 50.5S. To corroborate this trend detected on the altimeter data, the HS anomaly estimated from in situ PIRATA data at (10S, 10W) shows a trend of 2.6 x 10^5 J m^-2 y^-1. Oddly, this decadal scale increase in the HST is found only in the South Atlantic ocean stressing its important role in the climate variability of the world oceans..Pages: 1365-137

Construção de perfis de temperatura a partir de dados de Satélites,Climatologia e dados in situ

A aquisição de dados da estrutura termohalina dos oceanos sempre foi limitada pelo alto custo das missões oceanográficas. Sistemas de amostragem in situ menos dispendiosos, como o lançamento de XBTs por navios de oportunidade, a utilização de bóias de deriva, e mais recentemente, de sistemas de observação autõnomos como gliders e flutuadores Argo, foram concebidos como alternativas aos cruzeiros. Estes sistemas são capazes de cobrir vastas porções oceanicas e de fornecer grande quantidade de medições, porem seus dados nem sempre estão disponíveis ou mesmo são adequados `a resolução de um determinado problema ou ao estudo de um fenômeno em questão, devido principalmente à sua falta de sinopticidade e/ou cobertura espacial irregular. Sensores orbitais provaram ser valiosos e comparativamente possuem excelente periodicidade e cobertura espacial, mas suas observações são limitadas apenas à superfície dos oceanos. Assim, a capacidade de se inferir com boa precisão a estrutura termohalina de feições oceanográficas à partir de uma amostragem reduzida e/ou utilizando medições¸ indiretas é desejável e vem sido aprimorada em diversos trabalhos. Métodos clássicos incluem o desenvolvimento de modelos de feição pelo ajuste de curvas paramétricas (e.g. GANGOPADHYAY et al., 1997; CHU et al., 1999) e a reconstrução de perfis utilizando modos EOF (e.g. CARNES et al., 1990; AGARWAL et al., 2007

Identificação de ondas de Rossby a partir de diagramas de Hovmoller da concentração de \ud clorofila entre as latitudes de 25o S e 45o S do Oceano Atlântico

Ondas de Rossby são ondas planetárias oceânicas de ocorrência quase global com comprimentos de onda da ordem de centenas a milhares de quilômetros, períodos da ordem de meses a anos e amplitudes superficiais da ordem de centímetros, causando anomalia da altura da superfície do mar (AASM). Transportando grandes quantidades de energia e influenciando diretamente a circulação de larga escala e o clima global, sua propagação de fase acontece sempre para oeste e sua velocidade é predominantemente uma função da latitude. É sabido que relações entre AASM e concentração de clorofila (CC) podem ser encontradas em todas as bacias oceânicas, \ud evidenciando uma clara influência de fenômenos físicos em fenômenos biológicos. O presente trabalho visa a identificação de ondas de Rossby através da visualização de dados de CC, que, quando comparados a de AASM, apresentaram comprimento, período e velocidade de fase conforme previsto teoricamente para ondas de Rossby baroclínicas do primeiro modo vertical. A região de estudo, entre as latitudes de 25o\ud S e 45o S, é caracterizada pela presença da Corrente do Atlântico Sul, da convergência subtropical e da faixa de rotacional nulo do vento e é, portanto, sede de importantes fenômenos oceanográficos de larga escala. Ambos os conjuntos de dados foram \ud obtidos por sensoriamento remoto e submetidos a uma cadeia de filtros bidimensionais de resposta impulsiva finita (FIR2D) cujo funcionamento de baseia no princípio de convolução entre a série temporal e uma matriz-filtro. Os sinais filtrados foram decompostos em componentes propagantes e não-propagantes e entre os propagantes foi feita a separação das componentes em diversas bandas espectrais definidas por seus períodos centrais. Diagramas de Hovmoller foram confeccionados e as velocidades de fase foram obtidas através da transformada de Radon. A \ud conclusão do trabalho evidenciou uma clara influência das ondas de Rossby sobre a distribuição de clorofila ao longo da região estudada

Observação da variação da frente Brasil-Malvinas por dados de temperatura da superfície do mar

The Brazil-Malvinas Confluence is formed by the encounter of the Brazil Current with the Malvinas Current at the South Atlantic ocean. This is one of the most energetic regions of the world oceans and it is characterized by intense meridional sea surface temperature gradients. Satellite data and in situ observations often reveal the presence of cyclonic and anticyclonic meanders and vortices at the Brazil-Malvinas Confluence region. The sea surface temperature (SST) fields of the Brazil-Malvinas Frontal region can be used to detect the position of the thermal front. However, at energetic regions like Brazil-Malvinas Confluence, the SST is not enough to define the mean position front with some precision. It is necessary to employ the sea surface temperature gradient like additional parameter in the trace of Brazil-Malvinas Front (BMF) in absence of other measures like salinity, for example. Our study involved the determination of the mean BMF and its meridional displacement on an interannual scale using a time series of sixteen years of Advanced Very High Resolution Radiometer (AVHRR) database from Pathfinder version 5 (V5) program. We detected a significant meridional variability of the mean position of the front most probably due to an increase in the Brazil Current flux.Pages: 7153-715

Can the Surface Quasi-Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

International audienceSatellite altimeters provide quasi-global measurements of sea surface height, and from those the vertically integrated geostrophic velocity can be directly estimated, but not its vertical structure. This study discusses whether the mesoscale (30-400 km) dynamics of three regions in the South Atlantic can be described by the surface quasi-geostrophic (SQG) theory, both at the surface and in depth, using outputs from an ocean general circulation model. At these scales, the model surface eddy kinetic energy (EKE) spectra show slopes close to k−5/3 (k−3) in winter (summer), characterizing the SQG and quasi-geostrophic (QG) turbulence regimes. We use surface density and temperature to (a) reconstruct the stream function under the SQG theory, (b) assess its capability of reproducing mesoscale motions, and (c) identify the main parameters that improve such reconstruction. For mixed layers shallower than 100 m, the changes in the mixed-layer depth contributes nine times more to the surface SQG reconstruction than the EKE, indicating the strong connection between the quality of the reconstruction and the seasonality of the mixed layer. To further explore the reconstruction vertical extension, we add the barotropic and first baroclinic QG modes to the surface solution. The SQG solutions reproduce the model density and geostrophic velocities in winter, whereas in summer, the interior QG modes prevail. Together, these solutions can improve surface correlations (>0.98) and can depict spatial patterns of mesoscale structures in both the horizontal and vertical domains. Improved spatial resolution from upcoming altimeter missions poses a motivating scenario to extend our findings into future observational studies