Meteorological context of the onset and end of the rainy season in Central Amazonia during the GoAmazon2014/5

The onset and demise of the rainy season in Amazonia are assessed in this study using meteorological data from the GoAmazon experiment, with a focus on the 2014-2015 rainy season. In addition, global reanalyses are also used to identify changes in circulation leading to the establishment of the rainy season in the region. Our results show that the onset occurred in January 2015, 2-3 pentads later than normal, and the rainy season during the austral summer of 2015 contained several periods with consecutive dry days in both Manacapuru and Manaus, which are not common for the wet season, and resulted in below-normal precipitation. The onset of the rainy season has been strongly associated with changes in large-scale weather conditions in the region due to the effect of the Madden-Julian Oscillation ( MJO). Regional thermodynamic indices and the height of the boundary layer did not present a significant difference between the onset and demise of the wet season of 2015. This suggests that local changes, such as those in the regional thermodynamic characteristics, may not have influenced its onset. Thus, variability of the large-scale circulation was responsible for regional convection and rainfall changes in Amazonia during the austral summer of 2014-2015.