Ernani de Lima Nascimento

A Multiple-Vortex Tornado in Southeastern Brazil

AbstractDuring the late afternoon hours of 24 May 2005 a severe weather outbreak occurred in the state of Sao Paulo, southeastern Brazil. Severe thunderstorms were observed ahead of a surface cold front, including a (Southern Hemisphere) cyclonic left-moving supercell that produced a multiple-vortex tornado in the outskirts of the town of Indaiatuba, Brazil (23.1°S, 47.2°W). A documentation of the multivortex structure of the tornado and of the cloud-base features is performed using still images from a video that recorded the event. Characteristics of the tornadic thunderstorm and the synoptic-scale environment in which it developed are examined using Doppler radar data, geostationary satellite imagery, surface and upper-air observations, and data from the National Centers for Environmental Prediction’s Climate Forecast System Reanalysis. The cloud base of the thunderstorm displayed morphological features associated with midlatitude tornadic supercells, including a low-level mesocyclone and a “clear slot”...

A New Look at the Identification of Low-Level Jets in South America

AbstractCriteria currently employed in algorithms that identify low-level jets (LLJs) in South America utilizing rawinsonde and gridded model data fail to detect an important number of LLJ events. ...

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.

Some mean atmospheric characteristics for snowfall occurrences in southern Brazil

Snowfall is considered a natural disaster in southern Brazil, where a little infrastructure exists up to prevent against the damage it induces, making snowfall forecast a matter of great interest in this region. The present article aims to describe the mean behavior of low, mid, and high atmospheric levels during snowfall occurrences in southern Brazil. Sea-level pressure (SLP), 1000–500 hPa atmospheric thickness, geopotential height at 500 hPa, and wind speed at 200 hPa have been analyzed. One hundred and ninety-six snowfall records from the conventional surface meteorological stations have been selected for the period from 1979 to 2015. The surface synoptic pattern associated with snowfall occurrences has been obtained from ERA-Interim reanalysis data with horizontal spatial resolution of

Numerical Simulations of the South American Low Level Jet in Two Episodes of MCSs: Sensitivity to PBL and Convective Parameterization Schemes

0.75^\circ \times 0.75^\circ

INFLUENCES ON ATMOSPHERIC BLOCKING REGIMES ON SOUTHERN BRAZIL ON SCENARIOS OF FUTURE CLIMATE CHANGE

0.75∘×0.75∘ and temporal resolution of 12 h. SLP fields show a high-pressure transient system displacement from the Pacific Ocean to northeastern Argentina. In addition, it is possible to relate snowfall with displacement of a low-pressure system on the coast of southern Brazil. Thickness fields indicate shallow cold air mass intrusions one day before snowfall. Such a cold air continues moving towards low latitudes during consecutive snowfall days and it may be responsible for frost events in climatologically warm regions. Finally, mid and high atmospheric levels show an eastward propagating wave amplified by the Andes.

CLIMATOLOGIA DA FUNÇÃO FRONTOGENÉTICA SOBRE A AMÉRICA DO SUL EM UM CENÁRIO DE CLIMA PRESENTE E FUTURO

The present study ivestigated in detail a serie of 184 wind gusts events originally discarded by Ferreira e Nascimento (2015), which presented a behavior not consistent with local convective activity by persist for several hours. This study aims to confirm or not the convective nature of these wind gusts. Using hourly data from automated weather stations maintained by Brazil National Weather Service (INMET), satellite imagery from the Geostationary Operational Environmental Satellite (GOES 12 and 13), weather radars data and final analysis data from the National Centers for Environment Prediction (NCEP) Global Forecast System (GFS-FNL) the 184 intese wind gusts episodes was analysed, some recorded by weather stations located at high elevations and other in the coastal region of brazilian south. After a detailed analysis only 9 wind gusts events were confirmed as convective origin. For the weather stations located in high altitudes the most frequently forcing mechanism to explain intense wind gusts persisting for several hours was not convective activity, but the presence of a flow from north-northeast like a low-level jet (LLJ). In the coastal stations the most wind gusts originated from low pressure systems in synoptic scale located near the coast of southern Brazil, as extratropical cyclones.

SIMULAÇÕES NUMÉRICAS EM ALTA RESOLUÇÃO DE UM COMPLEXO CONVECTIVO DE MESOESCALA COM DIFERENTES CONDIÇÕES INICIAIS E DE CONTORNO

The sensitivity of numerical simulations of the low level jet stream (LLJS) in South America to the choice of parameterization schemes for the planetary boundary layer (PBL) and for cumulus convection using the Advanced Research core of the Weather Research and Forecast (WRF) model was assessed for two cases in which the development of Mesoscale Convective Systems (MCSs) was observed in the La Plata Basin at the exit of the LLJS. The MCSs developed under distinct synoptic forcing. Overall, the general area over the La Plata Basin where the wind profiles met LLJS criteria was larger in the situation with stronger frontal forcing. Regarding the impact of the choice of the PBL parameterization scheme upon the simulated LLJS, the nonlocal Yonsei University (YSU) scheme displayed slightly better results for most simulations regardless of the cumulus parameterization scheme utilized. In fact, the characterization of the LLJS in the simulations exhibited no significant sensitivity to the choice of the cumulus parameterization. In situations under stronger [weaker] frontal forcing, less [more] dispersion among the simulations was found regarding the identification of the LLJS.