Analysis of different intraseasonal patterns of large-scale circulation over the Amazon

Abstract:

It is well known that the large-scale equatorial circulation known as the Madden-Julian Oscillation (MJO) has an important impact on the convective activity over South America. The Bolivian high is an upper-level (200 hPa) anticyclone that develops during the summer over the Bolivian Altiplano, a high plateau region of the Central Andes. The position and intensity of this high-pressure cell has been related to the seasonal variation in Amazonian rainfall. This study used the Real-time Multivariate MJO index created by Wheeler and Hendon to examine the impacts and intensification of Bolivian high using daily rainfall data from Tropical Rainfall Measuring Mission (TRMM) and 6-hourly atmospheric fields from the ECMWF Interim reanalysis (ERA Interim). Enhance of precipitation filtered for 20-100-day during 3 to 6 MJO phase is accompanied by a significant suppression of high level zonal winds near northern South Atlantic coast and vice versa, i.e., suppressed precipitation for the same filtered data is associated with an enhancement of the wind near South Atlantic coast, for 8 to 1 phase. Intensification and positioning slightly more southwest of the Bolivian high was observed when there was an increase in convection associated with MJO. This convection enhancement increases the magnitude of the divergence at high levels that consequently favored convection.