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São José dos Campos, Brazil

Pereira Filho A.J.,University of Sao Paulo | Pezza A.B.,University of Melbourne | Simmonds I.,University of Melbourne | Lima R.S.,Brazilian Enterprise of Airport Infra Structure INFRAERO | Vianna M.,VM Oceanica LTDA
Atmospheric Research | Year: 2010

This work explores in detail synoptic and mesoscale features of Hurricane Catarina during its life cycle from a decaying baroclinic wave to a tropical depression that underwent tropical transition (TT) and finally to a Category 2 hurricane at landfall over Santa Catarina State coast, southern Brazil. This unique system caused 11 deaths mostly off the Brazilian coast and an estimated half billion dollars in damage in a matter of a few hours on 28 March 2004. Although the closest meteorological station available was tens of kilometres away from the eye, in situ meteorological measurements provided by a work-team sent to the area where the eye made landfall unequivocally reproduces the tropical signature with category 2 strength, adding to previous analysis where this data was not available. Further analyses are based mostly on remote sensing data available at the time of the event. A classic dipole blocking set synoptic conditions for Hurricane Catarina to develop, dynamically contributing to the low wind shear observed. On the other hand, on its westward transit, large scale subsidence limited its strength and vertical development. Catarina had relatively cool SST conditions, but this was mitigated by favourable air-sea fluxes leading to latent heat release-driven processes during the mature phase. The ocean's dynamic topography also suggested the presence of nearby warm core rings which may have facilitated the transition and post-transition intensification. Since there were no records of such a system at least in the past 30 years and given that SSTs were generally below 26 °C and vertical shear was usually strong, despite all satellite data available, the system was initially classified as an extratropical cyclone. Here we hypothesise that this categorization was based on inadequate regional scale model outputs which did not account for the importance of the latent heat fluxes over the ocean. Hurricane Catarina represents a dramatic event on weather systems in South America. It has attracted attention worldwide and poses questions as whether or not it is a symptom of global warming. © 2009 Elsevier B.V.

Vianna M.L.,VM Oceanica LTDA | Menezes V.V.,Brazilian Navy Research Institute
Journal of Geophysical Research: Oceans | Year: 2011

We present here a study of the mean upper layer structure of the South Atlantic Subtropical Gyre (SASG) and its modes of variability based on Archiving, Validation, and Interpretation of Satellite Oceanographic data sea level anomaly data, Gravity Recovery and Climate Experiment-based mean dynamic topography (MDT) models, Reynolds sea surface temperatures, and two tide gauge time series from Permanent Service for Mean Sea Level. Analysis of the MDTs shows that the SASG mean structure is represented by a double-cell circulation, the southern cell being a narrow quasi-zonal strip centered around 33°S. Its southern limb is limited by the recently discovered Saint Helena Current/Tristan da Cunha Current (StHC/TCC) and the North Subtropical Front around 35°S. This system is shown to be well separated from the South Atlantic Current/South Subtropical Front around 42-45°S. A method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band-passed data sets. The altimeter sea level trend analysis suggests that the SASG pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5-10 mm/yr occurring in the southern cell. Flow intensifications in this period (2-3 cm/s in the South Equatorial Current and North Brazil Undercurrent, 3.5 cm/s in the Benguela Current), and weakening by 4.5 cm/s in the StHC/TCC are recorded. The altimeter-derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges. Copyright 2011 by the American Geophysical Union.

Menezes V.V.,CSIRO | Menezes V.V.,University of Tasmania | Vianna M.L.,VM Oceanica LTDA | Phillips H.E.,University of Tasmania
Journal of Geophysical Research: Oceans | Year: 2014

A new milestone has been reached with the launch of two dedicated satellite missions to routinely measure the sea surface salinity (SSS) fields from space at global and regional scales. In the present work, a thorough analysis of the first 2 years of Aquarius SSS data in the South Indian Ocean is performed. This analysis is focused on three questions: How accurate is Aquarius SSS related to in situ data from the fresh Indonesian Throughflow and salty subtropical waters? Can Aquarius give a spatial context for the data measured by the RAMA mooring system? Are westward propagating annual-period signals described in recent model simulations reproduced by Aquarius-derived SSS? We find Aquarius observations to be highly correlated with those of Argo floats, with small disagreements occurring near oceanic fronts. Aquarius gives fresher SSS than in situ data in the tropical region due to rainfall effects, except in the eastern basin where the freshening seems to be related to sharp localized leakages of very fresh waters from the Indonesian seas that the Aquarius product is not able to properly resolve. Aquarius data are shown to reproduce quite well the annual cycle obtained from RAMA and Argo gridded data sets. The annual cycle in Aquarius is characterized by SSS propagating features with different characteristics west and east of the Ninety East Ridge. These features are strikingly different from sea surface height waves. Our results suggest that SSS annual propagation might be reflecting coupled ocean-atmosphere dynamics and surface-subsurface processes operating over the entire South Indian Ocean. Key Points Aquarius data are highly correlated with those of Argo and RAMA buoys SSS propagation pattern can be interpreted as a superposition of wave modes Annual SSS propagations are strikingly different from SSHA waves © 2014. American Geophysical Union. All Rights Reserved.

Vianna M.L.,VM Oceanica LTDA | Menezes V.V.,VM Oceanica LTDA | Pezza A.B.,University of Melbourne | Simmonds I.,University of Melbourne
Journal of Geophysical Research: Oceans | Year: 2010

The unexpected evolution of the first recorded South Atlantic Hurricane Catarina over waters with homogeneous sea surface temperatures (SST) of 24°C in March 2004 was a challenge to the weather forecast community. This work concentrates on a thorough data-driven comparative analysis to make reliable diagnostics of the role of the ocean in the genesis and evolution of Catarina. We used several high-resolution multisatellite-derived products, including three microwave-based SST data sets, multisatellite collinear data of sea surface height (SSH) anomalies, significant wave heights and wind speeds, four QuikSCAT ocean surface wind vector products (including the 12.5 km resolution swath data), daily fields of absolute objectively analyzed SSH and corresponding geostrophic currents, and Argo floats. The synergic use of these data sets showed that Catarina interacted strongly with four warm core rings (WCRs), forcing upwelling of isotherms and mixed layer waters. These interactions minimized the known negative SST feedback, as attested by the SST differences being less than 1.2°C. Although the SST in the region was around 24°C, below the Palmén threshold, the surface air temperatures were 14°C which still furnished a large air-sea temperature gradient capable of extracting large enthalpy fluxes from the WCRs influenced by Ekman pumping. It is shown here that Catarina achieved category 1 over the ocean on 26 March with its maximum intensity of 34 m/s seen in the 12.5 km swath winds. © 2010 by the American Geophysical Union.

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