Impacts of a large extra-tropical cyclonic system in Southern Brazilian Continental Shelf using the COAWST model

The Southern Brazilian Continental Shelf (SBCS) is an area with great ecological and economic importance to Brazil. In this region can be observed the recurrent passage of frontal systems and extra-tropical cyclones, which are more frequent during the winter months of the southern hemisphere. These systems act on the ocean surface layers as direct driving forces, which may change the thermohaline structure of the water column and induce sea level perturbations. This study used the coupled ocean-atmosphere regional model (COAWST) to evaluate the effect of the passage of a frontal system associated with an extra-tropical cyclone. The ROMS oceanic model was configured with two nested grids, in order to solve the hydrodynamic processes at different scales. The parent (20–40° S/40–60° W) and child (25–29.3° S/46.3–50° W) grid comprise the coastal region, with a horizontal resolution of 1/9° and 1/27°, respectively, with 32 vertical levels. The initial conditions are the Global Analysis Forecast from CMEMS and forcing files used the Climate Forecast System v.2 (CFSv2) data, from NCEP. This event took place on the continental shelf of the State of Santa Catarina, in September of 2016. The model results were compared to remote sensing data and to the tide gauges from the City of Imbituba (State of Santa Catarina, Brazil). The comparison showed a correlation higher than 78 % between sea level rise data and the model results. The filtering of sea level data made it possible to identify the meteorological component in the model results. The comparison between the tidal-gauge and the model output presented values under 25 cm. The model was capable of representing the sea level anomalies propagation associated with the passage of the atmospheric frontal system. The model output showed the presence of a sea level anomaly propagating northward along the continental shelf at 480 km day−1, probably associated with the presence of a coastal-trapped wave.

Friagens no Pantanal, Brasil: Ocorrência de Casos Gerais, Intensos e Análise Sinótica do Evento mais Intenso

No Pantanal, a ocorrência de friagem muitas vezes causa prejuízos econômicos e sociais, mas pouco são os estudos que investigaram o fenômeno na região. Portanto, o objetivo deste estudo foi caracterizar os casos gerais e intensos de eventos de friagens na região do Pantanal ocorridos entre 2007 e 2014, e caracterizar o ambiente sinótico do evento mais intenso de friagem. Para tal, utilizou-se dados de boletins do Climanálise, temperatura do ar da cidade de Coxim-MS e reanálises do MERRA-2. Verificou-se 72 eventos de friagens dos casos gerais e 27 casos intensos, sendo a maior frequência o ano de 2010 e os meses de agosto para casos gerias; e 2010 e 2013 e julho e agosto para casos intensos. Ocorreram 9 friagens.ano-1 para caos gerais e 3,4 friagens.ano-1 nos casos intensos. O estudo sinótico mostrou a configuração de um ciclone no oceano Atlântico a leste do sul do continente da América do Sul, relacionado à ampliação da onda baroclínica em altos níveis, com um anticiclone pós-frontal migratório em superfície acompanhado de ômega negativo e gradiente de espessura da camada (camada fria). Pantanal colds, Brazil: Occurrence of general, intense cases and synoptic analysis of the event A B S T R A C TIn the Pantanal, the occurrence of friagem often causes economic and social damages, but few studies have investigated the phenomenon in the region. Therefore, the objective of this study was to characterize the general and intense cases of friary events in the Pantanal region between 2007 and 2014, and to characterize the synoptic environment of the most intense cold event. For that, data of Climanálise bulletins, air temperature of the city of Coxim-MS and reanalysis of MERRA-2 were used. There were 72 friar events of the general cases and 27 intense cases, the highest frequency being the year of 2010 and the months of August for the gerous cases; and 2010 and 2013 and July and August for intense cases. There were 9 friagens.ano-1 for general chaos and 3,3 friagens.ano-1 in intense cases. The synoptic studys howed the configuration of a cyclone in th e Atlantic Oceaneastof the South American continent, related tothe amplification of the baroclinic waveat high levels, with a migratory post-frontal anticyclone on the surface accompanied by omega negative and thickness gradient of the layer (cold layer).Keywords: frontal system, air temperature, air polar, climatology.

Nonclassic Evolution of a Cold-Frontal System across the Western United States during the Intermountain Precipitation Experiment (IPEX)

A cold-frontal passage through northern Utah was studied using observations collected during intensive observing period 4 of the Intermountain Precipitation Experiment (IPEX) on 14–15 February 2000. To illustrate some of its nonclassic characteristics, its origins are considered. The front developed following the landfall of two surface features on the Pacific coast (hereafter, the cold-frontal system). The first feature was a surface pressure trough and wind shift associated with a band of precipitation and rope cloud with little, if any, surface baroclinicity. The second, which made landfall 4 h later, was a wind shift associated with weaker precipitation that possessed a weak temperature drop at landfall (1°C in 9 h), but developed a stronger temperature drop as it moved inland over central California (4°–6°C in 9 h). As the first feature moved into the Great Basin, surface temperatures ahead of the trough increased due to downslope flow and daytime heating, whereas temperatures behind the trough decreased as precipitation cooled the near-surface air. Coupled with confluence in the lee of the Sierra Nevada, this trough developed into the principal baroclinic zone of the cold-frontal system (8°C in less than an hour), whereas the temperature drop with the second feature weakened further. The motion of the surface pressure trough was faster than the posttrough surface winds and was tied to the motion of the short-wave trough aloft. This case, along with previously published cases in the Intermountain West, challenges the traditional conceptual model of cold-frontal terminology, structure, and evolution.

Condições atmosféricas de grande escala associadas a três eventos de tornados ocorridos no Estado do Rio Grande do Sul, Brasil (Large scale atmospheric conditions associated with three tornado events occurred in Rio Grande do Sul State, Brazil)

Os tornados são fenômenos atmosféricos extremos de rápida atuação e desenvolvimento podendo ocasionar prejuízos em diversos setores econômicos e sociais. Com o objetivo de compreender o ambiente favorável para o desenvolvimento de tempestades tornádicas, foram realizadas análises das condições atmosféricas para os episódios de tornados ocorridos nos municípios de Canela, Tapejara e São Miguel das Missões, no Estado do Rio Grande do Sul. Desta forma, foram utilizadas imagens de satélite da Geostationary Operational Environmental Satellite (GOES-13) e dados de reanálise do modelo Modern-Era Retrospective Analysis for Research and Applications (MERRA-2). A partir destes dados foram gerados campos atmosféricos e diagramas Skew-T/Log-P para avaliar a estrutura tridimensional da atmosfera e a eficiência dos índices convectivos na identificação do fenômeno. Entre os resultados obtidos, foi possível identificar que todos os casos estiveram associados a um sistema pré-frontal, a atuação do Jato de Baixos Níveis (JBN), com magnitude de vento superior a 16 m s-1 (850 hPa) e a atuação da corrente de jato (250 hPa) sobre as localidades atingidas. Ressaltando que no caso de Canela foi verificado o acoplamento entre o JBN e a corrente de jato e no caso de Tapejara foi observada a difluência do escoamento em 250 hPa. Outra característica encontrada foi a posição do eixo do cavado no nível de 500 hPa gerando advecção de vorticidade ciclônica e movimento ascendente sobre a região. Isso induziu a convergência de umidade na baixa troposfera (850 hPa), tornando-se uma das principais forçantes que propiciaram a intensificação da atividade convectiva na região. A B S T R A C TTornadoes are extreme atmospheric phenomena of rapid actuation and development and can cause damages in several economic and social sectors. In order to understand the favorable environment for the development of tornadic storms, atmospheric conditions were analyzed for the episodes of tornadoes occurring in the municipalities of Canela, Tapejara and São Miguel das Missões, in Rio Grande do Sul State. Thus, satellite images from the Geostationary Operational Environmental Satellite (GOES-13) and the Modern-Era Retrospective Analysis for Research and Applications – Version 2 reanalysis data were used. From these data atmospheric fields and Skew-T/Log-P diagrams were generated to evaluate the three-dimensional structure of the atmosphere and the efficiency of the convective indexes in the identification of the phenomenon. Among the results, it was possible to identify that all the cases were associated to a pre-frontal system, the performance of the Low Level Jet (LLJ), with a 850 hPa wind magnitude greater than 16 m s-1 and the actuation of the 250 hPa jet stream on the affected localities. Note that in the Canela case the coupling between the LLJ and the jet stream was verified and in the case of Tapejara the flow diffluence was observed at 250 hPa. Another characteristic found was the position of 500 hPa trough axis generating advection of cyclonic vorticity and ascending motion on the region. This induced the convergence of humidity in the lower troposphere (850 hPa), becoming one of the main forcing that led to the intensification of the convective activity in the region.Keywords: Low Level Jet, difluence, frontal system, convective index, severe storm.

Modelling the Effects of Aerosol on Mei-Yu Frontal Precipitation and Physical Processes

The Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the response of aerosols on the Mei-Yu frontal precipitation. The results indicate that increasing droplet concentrations lead to significant precipitation enhancement with the current pollution levels in Mei-Yu frontal system. Under the polluted conditions, the enhanced cold-cloud process is of great importance. Moreover, with the “towing” of active cold-cloud process, cold-cloud and warm-cloud processes developed mutually. These account for the complicated and special microphysical mechanism for aerosol impacts on Mei-Yu frontal system. Furthermore, two types of “microphysical-dynamic positive feedback loop” caused by the interactions of various physical processes and effects (direct dynamic effect, frontogenesis effect, and vapor pump effect) can be found in the Mei-Yu precipitation, which in turn reinforce the microphysical processes. The combined effect is to increase Mei-Yu front precipitation. The interaction of microphysical processes and dynamic processes, and the positive feedback loops they create are the main physical mechanisms behind the significant impacts of aerosol on Mei-Yu frontal precipitation. This may also be an important feature of climate change in eastern Asia.

Phytoplankton response to a plume front in the northern South China Sea

Due to a strong river discharge during April–June 2016, a persistent salinity front, with freshwater flushing seaward on the surface but seawater moving landward at the bottom, was formed in the coastal waters west of the Pearl River estuary (PRE) over the northern South China Sea (NSCS) shelf. Hydrographic measurements revealed that the salinity front was influenced by both the river plume and coastal upwelling. On shipboard nutrient-enrichment experiments with size-fractionation chlorophyll a measurements were taken on both sides of the front as well as in the frontal zone to diagnose the spatial variations of phytoplankton physiology across the frontal system. We also assessed the size-fractionated responses of phytoplankton to the treatment of plume water at the frontal zone and the sea side of the front. The biological impact of vertical mixing or upwelling was further examined by the response of surface phytoplankton to the addition of local bottom water. Our results suggested that there was a large variation in phytoplankton physiology on the sea side of the front, driven by dynamic nutrient fluxes, although P limitation was prevailing on the shore side of the front and at the frontal zone. The spreading of plume water at the frontal zone would directly improve the growth of microphytoplankton, while nano- and picophytoplankton growths could have become saturated at high percentages of plume water. Also, the mixing of bottom water would stimulate the growth of surface phytoplankton on both sides of the front by altering the surface N∕P ratio to make it closer to the Redfield stoichiometry. In summary, phytoplankton growth and physiology could be profoundly influenced by the physical dynamics in the frontal system during the spring–summer of 2016.