Ronald Buss de Souza

Atmospheric boundary layer adjustment to the synoptic cycle at the Brazil‐Malvinas Confluence, South Atlantic Ocean

[1] This study analyzes and discusses atmospheric boundary layer vertical profiles of potential temperature, specific humidity, and wind speed at each of the sides of the Brazil-Malvinas Confluence in the southwestern Atlantic Ocean. Such confluence is characterized by the meeting of water masses with very different characteristics: the southern waters of the Malvinas current can be several degrees colder and appreciably less salty than the northern Brazil current waters. At the same time, a synoptic cycle can be identified at the region, marked by the successive passages of frontal systems and extratropical cyclones. The different phases of the synoptic cycle lead to different thermal advections at the confluence, causing respective different patterns of atmospheric boundary layer adjustment to the surface heterogeneity induced by the confluence. In the present study, this adjustment along the synoptic cycle is analyzed using data from five experiments performed across the confluence from 2003 to 2008. In each of the campaigns a number of soundings were launched from a ship at both sides of the confluence. A climatological analysis with respect to the closest frontal passage is presented, and it suggests that the observations collected at each of the years analyzed are referent to a different day of the synoptic cycle. The average profiles at each side of the confluence are in agreement with previous modeling studies of warm and cold thermal advection patterns over an oceanic front. Furthermore, our study shows that peculiar transitional characteristics are also observed between the conditions of well-established warm and cold advection. At many phases of the synoptic cycle a strongly stratified boundary layer occurs at one or both sides of the confluence. Some of the observed characteristics, such as a large moisture accumulation near the surface, suggest that existing sensible and latent heat fluxes parameterizations fail under very strong stratifications, and the consequences of this deficiency are analyzed.

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

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.

Variabilidade das anomalias de temperatura da superfície do mar no oceano atlântico sudoeste e sua relação com o fenomeno El Niño-Oscilação Sul

This work presents a study on the variability of satellite-derived sea surface temperature anomaly (SSTA) fields in regions under the influence of different oceanographic and/or biophysical patterns in the South-western Atlantic Ocean (SWA). In order to accomplish that, time series of SSTA from 1985 to 2006 were investigated over nine sub-areas in the SWA, divided into the subtropical, intermediate and sub Antarctic domains. Spectral analysis applied to the SSTA time series reveled cycles in the interannual period between 1.6 and 3.7 years. Cross correlation analysis was used aiming to establish the relation between the cycles present in the SSTA and the El Nino - Southern Oscillation (ENSO) events, represented here by the Multivariate ENSO Index (MEI). The results show a statistically significant, lagged in time, correlation between the ENSO and thermal anomalies in the SWA, however there is no direct association between the warm (cold) El Nino (La Nina) episodes with positive (negative) SSTAs. Among all distinct study areas, the maximum correlation occurs in the Brazil-Malvinas Confluence region (-0,78), with a time lag of 9 months after the La Nina of May 1988 to May 1989.

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

The Southern Brazilian Continental Shelf (SBCS) is one of the more productive areas for fisheries in Brazilian waters. The water masses and the dynamical processes of the region present a very seasonal behavior that imprint strong effects in the ecosystem and the weather of the area and its vicinity. This paper makes use of the Regional Ocean Modeling System (ROMS) for studying the water mass distribution and circulation variability in the SBCS during the year of 2012. Model outputs were compared to in situ, historical observations and to satellite data. The model was able to reproduce the main thermohaline characteristics of the waters dominating the SBCS and the adjacent region. The mixing between the Subantarctic Shelf Water and the Subtropical Shelf Water, known as the Subtropical Shelf Front (STSF), presented a clear seasonal change in volume. As a consequence of the mixing and of the seasonal oscillation of the STSF position, the stability of the water column inside the SBCS also changes seasonally. Current velocities and associated transports estimated for the Brazil Current (BC) and for the Brazilian Coastal Current (BCC) agree with previous measurements and estimates, stressing the fact that the opposite flow of the BCC occurring during winter in the study region is about 2 orders of magnitude smaller than that of the BC. Seasonal maps of simulated Mean Kinetic Energy and Eddy Kinetic Energy demonstrate the known behavior of the BC and stressed the importance of the mean coastal flow off Argentina throughout the year.

Uma Revisão dos Processos de Interação Oceano-Atmosfera em Regiões de Intenso Gradiente Termal do Oceano Atlântico Sul Baseada em Dados Observacionais

In a general view, the interaction of the ocean with the atmosphere in regions of intense oceanic mesoscale activity (oceanographic fronts, meanders and eddies typical of spatial scales of about 100-500 km and time scales of about 2-3 months) presents a positive correlation between the sea surface temperature (SST) and meteorological variables such as the stability of the Marine Atmospheric Boundary Layer (MABL), the wind intensity and the heat, momentum and gas fluxes between the ocean and the atmosphere. This suggests that the ocean forces the atmosphere at the spatial and temporal scales related to the oceanic mesoscale. Mostly based on observational data, this work presents a brief scientific revision on the impact of the mesoscale structures present in the Southwestern Atlantic Ocean on some components of the coupled ocean-atmosphere system that, in certain aspects, impact the weather and the climate of the adjacent continental regions of South America. It is also included in this article a brief review of the state of the art knowledge about the oceanic part of the South Atlantic Convergence Zone. This paper presents the general oceanographic characteristics of the study area, including some aspects about the South Atlantic circulation and variability. Recalling the fact that the subtropical South Atlantic is a Storm Track region, this paper also discusses the impacts of the SST gradients of the Southwestern Atlantic Ocean on the transient atmospheric systems that frequently cross the region. In addition, the paper discusses novel indications that the oceanographic processes occurring at the southern coast of Brazil in wintertime have a marked impact on the MABL modulation over the southern Brazilian continental shelf. The paper reports past and present indications that the ecological processes caused by the atmospheric and marine climate variability of the southern coast of Brazil impact the spawning and catches of the Brazilian sardine (Sardinella brasiliensis), one of most important renewable marine resources of Brazil. The paper finishes presenting some of the current observational efforts of Brazil aiming the collection of marine meteorology data in the South and Equatorial Atlantic Ocean. These efforts intend to widen our understanding of the ocean-atmosphere coupling at the synoptic and climatic scales as well as the role of the Atlantic Ocean in controlling the heat, momentum and carbon dioxide fluxes to the atmosphere.

Análise do Desempenho do Modelo Weather Research and Forecasting (WRF) com Diferentes Esquemas de Microfísica e Camada Limite Planetária na Ilha Deception, Antártica

Diferentes esquemas de CLP e microfisica do modelo WRF sao comparados em uma pequena ilha na Antartica com um lago com atividade geotermal em seu interior. Dados coletados em uma torre micrometeorologica sao comparados com o modelo para 3 dias de situacoes atmosfericas distintas: nebulosidade baixa, ceu relativamente claro e a passagem de um ciclone sobre a ilha.Para a temperatura do ar, osdiferentes experimentos resultam num ciclo diario de menor amplitude que os observados. A variabilidade entre os esquemas e menor que 1 °C, devido a influencia da TSM e a sua diferente capacidade em reproduzir nebulosidade. Para o dia de ceu claro, a previsao de radiacao de onda curta depende fortemente do esquema microfisico utilizado e pouco dos esquemas de CLP. Para a radiacao de onda longa os esquemas produzem resultados semelhantes, porem quando ha ciclone atuando o esquema THOMPSON tem melhor desempenho que o WSM3.Para o vento zonal, a variabilidade entre os esquemas de CLP e geralmente maior (1 a 3 m/s) que entre os de microfisica (menor que 1 m/s). O esquema WSM3 e, em geral, mais indicado para as previsoes nos dias de ciclone. Para a componente meridional do vento observa-se pouca diferenca entre os esquemas microfisicos e CLP.

ANALYSIS OF THE OCEAN-ATMOSPHERE COUPLING AT THE SYNOPTIC SCALE ALONG 33 °S ON 19 AND 20 JUNE 2012

The southern coast of Brazil is marked during winter by the presence of an oceanographic front between the Brazil Current (BC) and the Brazilian Coastal Current (BCC). The BC/BCC oceanographic front imprints intense thermal gradients between the cold (BCC) waters of the continental shelf and the warm (BC) waters of the deep ocean. This work analyses, for the first time in the known literature, the ocean-atmosphere coupling using observational data taken by ship during 19-20 June 2012 along a transect off the coast of RS State, Brazil. During the period when the data were collected, a cold (post-frontal) air mass penetrated the study region causing an elevation of the atmospheric pressure and a diminution of the air temperature. Data from radiosondes launched in both sides of the oceanographic front indicate an atmospheric boundary layer thicker and more turbulent above the BC in respect to the BCC. The heat fluxes were positive along the entire transect although presenting a big variation in magnitude. Simultaneos in situ observations of both oceanographic and meteorological parameters are necessary for the understanding of the coupled ocean-atmosphere system, having primal importance for the weather prediction.

SIMULAÇÃO EM ALTA RESOLUÇÃO COM WRF UTILIZANDO A PARAMETRIZAÇÃO DE JANJIC NA BAÍA DA ILHA DECEPTION

The WRF model was run using the planetary boundary layer scheme from Janjic (2002), centered in the bay of Deception Island. The air temperature correlation was 0.95, while for the dew point temperature the correlation was 0.73. The surface atmospheric pressure was the better represented variable, with a correlation of 0.99. Finally, the wind intensity showed a lower correlation of 0.62, with a greater tendency of the model to underestimate the observations.

AVALIAÇÃO DO MODELO WRF EM RELAÇÃO À TEMPERATURA DO AR E PRESSÃO ATMOSFÉRICA DEVIDO À PASSAGEM DE UMA FRENTE FRIA SOBRE A ILHA DECEPTION, ANTÁRTICA

Foi verificado que as interacoes fisicas modelo WRF (Weather Research and Forecasting) podem ser comparadas com os dados coletados na Ilha Deception para permitir aprimoramentos das simulacoes. Neste trabalho, foi feito a analise de duas variaveis meteorologicas (temperatura do ar e pressao atmosferica) em situacoes pos e pre-frontal. Em relacao a essas variaveis estudadas, observou-se que o WRF mostrou um melhor desempenho para a pressao atmosferica, pois esta depende dos padroes meteorologicos de grande escala.

INFLUÊNCIA DAS ANOMALIAS DA TEMPERATURA DA SUPERFÍCIE DO MAR EM REGIÕES DE LATITUDES MÉDIAS E ALTAS NA TRAJETÓRIA PREFERENCIAL DOS CICLONES EXTRATROPICAIS SOB CONDIÇÕES CLIMÁTICAS DE AQUECIMENTO GLOBAL

A influencia da anomalia na TSM no deslocamento da dos ST num cenario sob influencia de aquecimento global e investigada em latitudes medias e altas atraves de simulacoes do Modelo de Circulacao Geral Atmosferica (MCGA), ECHAM5/MPI-OM. As variacoes da temperatura da superficie do mar parecem ter grande contribuicao na redistribuicao da atividade ciclonica no cenario climatico futuro evidenciadas pelas maiores anomalias positivas encontradas na regiao da passagem de Drake, confirmando o deslocamento dos Storm Tracks em direcao ao polo. Abstract: The influence of SST anomalies in the displacement of the ST a scenario under the influence of global warming is investigated in middle and high latitudes through simulations of the atmospheric general circulation model (AGCM), ECHAM5/MPI-OM. The variations of the surface temperature of the sea seem to have great contribution in the redistribution of cyclonic activity in future climate scenario evidenced by higher positive anomalies found in the region of the Drake Passage, confirming the shift of the Storm Tracks into the pole.