Padrões espaço-temporais do ambiente de formação de linhas de instabilidade tropicais amazônicas.

Abstract

The study purpose was to investigate the atmospheric patterns existing in environment with and without Squall Lines (SL) formation over city of Belém-PA. The Principal Component Analysis technique was applied to the days groups with SL (SL) and without SL (wSI), in each quarter, from 2000 to 2016. Correlations and temporal patterns were determined for the quarters of each group, aiming to explain and better understand the atmospheric processes involved in the IL formation environment. From the selected PCA temporal common factors, the zonal and meridional components of the wind vertical mean profiles, and wind flow and specific humidity mean spatial fields in an area covering all of South America and parts of the adjacent oceans. The results showed that the SL formation environment is formed by a moderate shear in the layer closest to the surface, which is more intense in the LI each quarter group. This shear results in low level jet (LLJ) formation and possibly occurs due to the SASH intensification and, consequently, of Northeast trades on the South America north coast, entering the continent in a perpendicular direction to the coast. Therefore, it is a factor responsible for the greater spread of SL, especially in MAM. The patterns observed around the 700 and 500 hPa levels reflect the LLJ characteristics in terms of its best definition. It was observed that the Northeast trades intensification and more southern ITCZ action enhance the transport of moisture from the ocean to the continent, which favors the SL formation. In DJF and MAM quarters, the humidity on South America north coast also comes from Amazon rainforest. In JJA quarter, there is an SASH intensification and, despite the ITCZ being located in more northern latitudes, there is a higher moisture content in the pattern associated with the SL days. In wLI days pattern, the ITCZ is more northward, with discontinuous moisture nuclei. Another striking feature in JJA quarter SL day pattern is the presence of moisture dipole at 700 hPa level. It is confirmed that the ITCZ displaced further to south is the main system that acts directly in the formation of Amazonian SL in all quarters. In addition, the SACZ further north presence of its average position and with greater intensity and the higher frequency of SALLJ in the SON and DJF quarters, help the formation of SL. In JJA, it was also suggested that disturbances in the wind field influenced by the higher frequency of Easterly Wave Disturbances and by the more intense SASH closer to the continent, provide greater instability on South America north coast, favoring the SL formation.