Abstract This study aimed to classify the homogeneous regions of vegetation cover, which occur in Rio Grande do Sul, formed by clustering of pixels with same pattern of temporal variability of the Normalized Difference Vegetation Index (NDVI) of AVHRR GIMMS and MODIS series and to compare their temporal dynamics. We use K means cluster analysis for defining homogeneous regions, based on the temporal variability of GIMMS (8 km spatial resolution) and MODIS (1 km spatial resolution) NDVI data sets, using monthly images mean from 2000 to 2008 (overlapping period); and we analyzed the annual pattern of NDVI. Accuracy assessment was done with Landsat images. The results show that the temporal variability of GIMMS and MODIS NDVI allows to delimit similar homogeneous regions in order to mapping the main vegetation cover. MODIS series shows a greater detail in the definition of the regions, but with compatibility with those generated by GIMMS. The temporal dynamics show a typical seasonal pattern, with variations of NDVI amplitude between the groups, that allow to monitor phenological changes. The deviations from calibration between times series are linear, which would facilitate a correction in order to construct a long synthetic time series for studies of land cover change.

Abstract Six events of explosive cyclogenesis occurred in the south Atlantic were compared using reanalysis data and satellite water vapor imagery. Cases of different intensities (weak, moderate and strong) occurred during 2014 summer season and 2012 winter season were studied. Despite the similarities the tropopause anomaly was more prominent and vertical movements were stronger in the strong cyclogenesis cases. The tropopause anomalies behind the cold front and ahead of the warm front appear only in the mature stage of the weak and moderate cases while in the strong case it is already evident and more intense behind the cold front since the beginning of the cycle. In all the cases confluence of the jet streams took place at higher levels forming a jet streak with difluence occurring downstream and the cyclone beginning in the exit region. The trajectories of the cyclones were in the southeast direction but longer and more meridional in the strong cases. The results indicated the baroclinicity of the region as the main mechanism for the development of these cyclones as well as the amplitude of the upper level jet stream perturbation. Furthermore, all the explosive cyclones developed following the Shapiro & Keyser cyclone conceptual model.