Everson Dal Piva

Energetics of Winter Troughs Entering South America

Abstract The energetics and behavior of midtropospheric troughs over the Southern Hemisphere and their relationship with South America surface cyclogenesis were studied during the winters of 1999–2003. All surface cyclogenesis situations over Uruguay and adjacent areas associated with 500-hPa troughs were analyzed. The atmospheric circulation associated with type-B and type-C cyclones form the basis for two composites: composite B (with 25 cases) and composite C (with 13 cases). The results showed that the midtropospheric troughs were more intense in composite C than in composite B before the surface cyclogenesis and that the opposite occurred during the surface cyclogenesis. The baroclinic conversion was dominant in both composites. In composite B, the ageostrophic flux convergence (AFC) contributed positively to the intensification of the surface cyclone since it imported energy into the area before the cyclogenesis started. But in composite C, the AFC served as a sink because it exported energy. Based ...

Papel dos fluxos de calor latente e sensível em superfície associado a um caso de ciclogênese na Costa Leste da América do Sul

Numeric experiments were run with meteorological regional model with the purpose to verify the impact of both latent and sensible surface heat fluxes (FCL and FCS, respectively) during the development of an intense east cost cyclone over southeastern region of South America from 24 to 26 July, 1998. The intensification rate of the cyclone was reduced by 6 hPa/24 h in the experiment where the FCL and FCS were absents. It was also verified that the absence of FCL presented more impact than without FCS. The intensification rate was reduced by 6 hPa/24h in the experiment without FCL and became unaltered in the experiment without FCS, but in the later the isobar with minimum value around the cyclone center occupied a smaller area. The absence of the FCL and FCS generated a drier and colder layer near the oceanic surface, reducing the environmental potential instability and decreasing the cyclone intensification. With these results it is possible to conclude that the FCL and FCS were important before the phase of most rapid cyclone development, preparing the environment to a more intense cyclogenesis, supplying both energy and moisture to the lower troposphere. In the phase of the most rapid development, the available energy and moisture (inserted in the previous phase) in the lower levels were also important, allowing the cyclone to develop more intensely than it could be in a drier and less thermically unstable environment.

An Objective Study of 500-hPa Moving Troughs in the Southern Hemisphere

Abstract The location and movement of 500-hPa troughs using an automated method are studied with data from a 24-yr period with the objective of determining the trough formation and dissipation regions in the Southern Hemisphere. To identify the 500-hPa mobile troughs, an objective method that uses the Eulerian centripetal acceleration (ECA) is developed. On average, 868 troughs per year were identified by the method, with an increase in trend during the period studied. The troughs have an average lifetime of 4.3 days, being longer (shorter) in subtropical (high) latitudes. The average calculated phase velocity was 13.6 m s−1, being higher (lower) in middle (high) latitudes. The troughs are normally found in the 60°–40°S latitudinal band, with maximum occurrence at 50°S. The longitudinal distribution of trough genesis has three maximum regions: over the Drake Strait and the South Atlantic Ocean, over the Indian Ocean around 50°S, and over the southwestern Pacific Ocean between 150°E and 150°W. The trough d...

MULTI-LAYER ATMOSPHERIC ANALYSIS DURING SNOW EPISODES IN SOUTHERN BRAZIL

A climatology for thickness, temperature, absolute and relative humidities, and vertically-integrated water vapor is presented for a number of distinct atmospheric layers during snow episodes reported in Southern Brazil from January 1979 to March 2011, totaling 64 events. Data from “The Climate Forecast System Reanalysis” (CFSR) were used in the analysis of aforementioned variables for the following atmospheric layers: 850-1000 hPa, 7001000 hPa, 500-1000 hPa, and 700-850 hPa. The snow episodes were subdivided into three sets according to the local surface elevation. The thicknesses of the atmospheric layers found for the snow events in southern Brazil were considerably deeper than the corresponding ones documented in the literature for North America. In addition, analysis of the vertical distribution of water vapor, temperature and relative humidity in the lower troposphere indicated that the atmospheric layer with favorable conditions to snow production is relatively shallow, being below 850hPa. Moreover, the threshold value of thickness for the 850-1000h Palayer during snow occurrence in southern Brazil was around 133 dam, being considerably higher than its counterpart value documented for North America, highlighting the role played by the local topography in setting the conditions that are favorable for snow occurrence in Brazil.

EVALUATION OF DIFFERENT BOUNDARY LAYER SCHEMES FOR FOG EVENTS SIMULATION AND FORECASTING IN RIO GRANDE DO SUL

In this work we used two boundary layer schemes to reproduce numerically a persistent fog event in Santa Maria, Rio Grande do Sul. The model employed was WRF using, as initial and boundary conditions, GFS data. The boundary layer employed schemes were the Mellor-Yamada-Janic (MYJ) and Yonsei University (YSU). Generally, boundary layer overestimate of wind speed values schemes 10m and represent relatively well temperature. However, the relative humidity does not represent the fog condition, not reaching saturation in some cases. When saturation is achieved the same if not properly maintained during the occurrence of the event.

CONVECTIVE PARAMETRIZATION AND EXPICITY SIMULATION: SENSIBILITY TESTS FOR AMAZONIAN CONVECTIVE SYSTEMS

The WRF(Weather Research and Forecastiong Model) is used to simulate Mesoscale Convective Systems occurred between 18-21 june 2014 close to ZF-2/LBA experimental site, Manuas, AM, Brazil. The main objective is to verify the convective parametrization Betts-MillerJanjic, a deep layer controled scheme, and Kain-Fritsch, a low level control scheme in simulations of tropical storms over the Amazon. The simulation least 72h with nested domains of 12 and 3 km. The evolution of convective systems, convective mode, cold pools and outdrafts were observed. The convective scheme Kain-Fritsch reproduced realistics storms with convective mode, propagation and downdrafts which resembles the usual observations.

MEAN WEATHER CHARACTERISTICS ASSOCIATED TO RADIATION FOG AT SANTA MARIA–RS

Central Depression, is region of great importance for different activities in Rio Grande do Sul. This area is also characterizedfor the high frequency of fog formation, specially in Santa Maria. To identify fog occurrence, METAR message were used.Furthermore, automatic stations data have employed to eliminate fog events under rain conditions in day and day before theevent. The synoptic analysis was done with final data analysis by NCEP. It was observed that in colder months the events aremost frequent. Moreover, the fog occurence is correlated with anticyclone postion in relation to Santa Maria.

AVALIAÇÃO DO MODELO WRF COM DIFERENTES PARAMETRIZAÇÕES CONVECTIVAS PARA UM CASO DE CICLOGÊNESE NA BACIA DO PRATA

O impacto da escolha do esquema de parametrizacao convectiva na representacao da precipitacao associada a um caso de ciclogenese e analisado utilizando o modelo WRF. Os indices estatisticos ETS e BIAS score mostraram que para os limiares de chuva fraca a moderada, o esquema de ajuste convectivo de Betts-Miller-Janjic obteve uma melhor representacao da precipitacao.

Redução de escala de dados de vento de modelos regionais para Modelos de Dispersão Atmosférica

This paper discusses the development of a data interpolation scheme applicable to the regional numerical weather prediction models (i.e. BRAMS) output, allowing the coupling of these models with atmospheric dispersion models. To evaluate this tool, the BRAMS wind field is used as input to the Atmospheric Dispersion Model (Zimora) developed by the Laboratorio de Micrometeorologia of the Universidade Federal de Santa Maria (UFSM).

Avaliação do modelo BRAMS na formação de nevoeiro de radiação em ambiente com turbulência pouco desenvolvida

RESUMO Nevoeiro de radiacao e normalmente precedido por forte resfriamento noturno. Em determinados eventos, a magnitude deste resfriamento e tao intensa que os modelos operacionais de previsao de tempo nao conseguem representa-lo adequadamente. Simulacoes foram realizadas com o objetivo de reproduzir a formacao do nevoeiro de radiacao, observado na madrugada do dia 18 de abril de 2007. Foram testados parâmetros e parametrizacoes relacionados a turbulencia disponiveis no modelo BRAMS versao 3.2. Para o calculo do coeficiente de difusao vertical foram testados os esquemas de Mellor-Yamada e Smagorinsky, e para a razao entre os coeficientes de difusao vertical para escalares e para o momentum foram testados os valores 1 e 3. Os melhores resultados foram obtidos com o esquema de Mellor-Yamada e a razao 1 entre os coeficientes. A maxima taxa de resfriamento foi de -5,7 o C/10h e a taxa de umedecimento foi de 27,1%/10h, mas os dados observados indicaram valores de -8,8 o C/10h e 29%/10h, respectivamente. Com relacao aos erros e taxas de resfriamento e umedecimento em superficie, as opcoes testadas geraram apenas pequenas melhoras nos resultados, mas foram suficientes para desenvolver o nevoeiro em superficie. Palavras-Chave: Nevoeiro, modelo regional, previsao de tempo.