Connecting heavy precipitation events to outgoing longwave radiation variability scales: case analysis in Brazil

Abstract

Spatial fields of outgoing longwave radiation (OLR) spectrum variance are analyzed in different time-scales: synoptic, sub-monthly, intra-seasonal, during the 1979-2016 austral summer months in southern Brazil. Variability fields differ both in intensity and location and highlight dominant convection cycles in the study area. The results show that the amplitude of sub-monthly variability is greater than the other scales in the southeastern region of Brazil, while the synoptic scale prevails in the southern region. The above-mentioned scales show higher amplitudes over the western Pacific Ocean where the Madden-Julian Oscillation plays an important role, along the South Pacific Convergence Zone, and over the storm track areas over the South Pacific Ocean. The influence of spectral OLR scale interaction is also analyzed, associated to the occurrence of two intense rainfall events over the southeastern Brazil in the austral summers of 2011 and 2014 when the South Atlantic Convergence Zone was involved in both events. The results obtained suggest that spectral OLR scale interaction takes place in such way that it strengthens the South Atlantic Convergence Zone, since the spatial pattern footprints of the 2 to 8-day timescale (synoptic), 10 to 30-day timescale (sub-monthly) and 30 to 60-day timescale (intra-seasonal) overlap in the study region.