The skill of the diverse-based precipitation products is investigated in comparison with HYBAM raingauge observations. The performance of three remote sensing-based datasets (the Climate Hazards Group InfraRed Precipitation with Station, CHIRPS, the Multi-Source Weighted-Ensemble Precipitation, MSWEP, and the Tropical Rainfall Measuring Mission, TRMM) is evaluated considering different timescales for the Amazon Basin, an area with widely heterogeneous precipitation. The analysis considered seasonal, intraseasonal and diurnal timescales through the computation of the cluster analysis, the seasonality index, the Kling-Gupta E ciency metric, spectral analysis and composing technique. CHIRPS has the lowest performance to represent the rainfall in the northwest portion of the basin, where it underestimated the mean precipitation compared to the other bases. In this region, the other remote sensing-based (TRMM and MSWEP databases) compared to HYBAM also showed considerable variability and misrepresentation of the intraseasonal rainfall. In general, all databases perform better in the north and eastern portions of the basin compared to HYBAM. The comparison of the diurnal rainfall cycle between remote sensing-based data and the eld campaigns of TRMM-LBA and GoAmazon, and the Huayao station in the Andes was also evaluated. At the diurnal timescale, MSWEP predates the time of the rainfall peak, but represents the magnitude of the precipitation well compared with TRMM. This study is necessary to warn about the importance of a more complete and objective assessment of the data before considering it for applications in different precipitation studies, mainly in regions with high rainfall heterogeneity like the Amazon Basin.
A Serra da Mantiqueira localiza-se na região sudeste do Brasil e, devido sua altitude, possui clima apto para cultivos como o café. Portanto, a ocorrência de geadas nessa região causa grandes danos econômicos. Diante do exposto, o objetivo deste estudo é apresentar a frequência dos episódios de geadas em quatro localidades da Serra da Mantiqueira e uma análise das condições atmosféricas propícias a esse fenômeno meteorológico. Dentre os quatro locais estudados, a maior frequência anual de geadas ocorre em Campos do Jordão (SP), com registro de 22 casos, sendo seguido de Maria da Fé (MG) com 12 casos por ano. A condição mais propícia aos eventos de geada está associada com a atuação do setor oeste do Anticiclone Subtropical do Atlântico Sul sobre o sudeste do Brasil. Esse sistema causa condições de céu claro, o que facilita o resfriamento da superfície por perda radiativa noturna.
Instead of using the traditional space-time Fourier analysis of filtered specific atmospheric fields, a normal-mode decomposition method is used to analyze the South American intraseasonal variability (ISV). Intraseasonal variability is examined separately in the 30-90-day band, 20-30-day band, and 10-20-day band. The most characteristic structure in the intraseasonal time-scale, in the three bands, is the dipole-like of convection between the South Atlantic Convergence Zone (SACZ) and the central-east South America (CESA) region. In the 30-90-day band, the convective and circulation patterns are modulated by the large-scale Madden-Julian Oscillation (MJO). In the 20-30-days and 10-20-day bands, the convection structures are primarily controlled by extratropical Rossby wave trains. The normal-mode decomposition of reanalysis data based on 30-90-day, 20-30-day, and 10-20-day ISV show that the tropospheric circulation and CESA--SACZ convective structure observed over South America are dominated by rotational modes (i.e., Rossby waves, mixed Rossby-gravity waves). A considerable portion of the 30-90-day ISV has also been associated with the inertio-gravity (IGW) modes (e.g., Kelvin waves), prevailing mainly during the austral rainy season.The proposed decomposition methodology demonstrated that a realistic circulation can be reproduced, giving a powerful tool for diagnosing and studying the dynamics of waves and the interactions between them in terms of their ability to provide causal accounts of the features seen in observations.
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