Convecção profunda na Amazônia Central

Abstract

The Amazon region has the main ingredients for deep convection development: water vapor, instability and convective available potential energy (CAPE). But the march of daytime moist convection in this region is influenced by a complex interation of convective scales ranging from small to large scale. The main objective of this research is to understand the relationship between the moist convective activity and vertical distribution of water vapor in the Central Amazon. For this, precipitation data of four stations, cloud top temperature (CTT) and radiosondes were used. This database includes information from 2006 to 2011. The study area is approximately 4800 km2, centered on the city of Manaus-AM. Analysis is conducted at four sites, two representative of forest area and two representative of urban area. The metodology consisted primarily of evaluating seasonal and diurnal variability of rainfall in terms of intensity and frequency. Subsequently a classification of deep convection events based on the 95 % percentile of rainfall threshold values and CTT was realized. From selected events intensity and time of occurrence of rainfall from deep convection are obtained. Also humidity, temperature and wind profiles as well as the stability of the atmospheric column are analyzed. The results show that precipitation in forest areas is 20 % higher than in urban areas, especially in the early afternoon hours. The frequency of rain events varies with the time of the day, while the average rainfall intensity does not. For all stations, in the rainy season (NOV-MAY) the frequency of rainfall is approximately three times higher than in the dry season (JUNOCT) and the peak of daytime frequency in the afternoon is more pronounced in forest areas. Higher frequencies in the early morning hours near the river are possibly due to the effect of river breeze. Approximately 76.3 % of the intense rain events ( 20 mm/hora) are caused by deep convective events (DCE), which are more frequent in the rainy season and in forest areas. Among the vertical profiles of the atmosphere, humidity showed higher differences between DCE and other types of rain and no-rain events, principally in the 900 to 500 hPa layer. The humidity in this layer is decisive for the occurrence of the transition from shallow to deep convection. Finally, the CAPE analysis showed that the thermodynamic instability is not a limiting factor for the occurrence of deep convection, but for most less deep convective events (LDCE) and DCE it must be greater than 1000 J.kg��1, while for the shallow convective events (SCE) it always showed values less than 2500 J.kg��1.