Dynamic Characteristics of the Circulation and Diurnal Spatial Cycle of Outgoing Longwave Radiation in the Different Phases of the Madden–Julian Oscillation during the Formation of the South Atlantic Convergence Zone

Liviany P Viana,Jhonatan A A Manco,Dirceu Luis Herdies

doi:10.3390/atmos12111399

Liviany P Viana, Jhonatan A A Manco + Show 1 more

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https://doi.org/10.3390/atmos12111399

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Journal: Atmosphere	Publication Date: Oct 25, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: National Institute for Space Research

Abstract

In this work, we verified the formation of the South Atlantic Convergence Zone (SACZ) during the active, unfavorable, and transition phases of the Madden–Julian Oscillation (MJO), as well as the diurnal spatial variability in the estimated Outgoing Longwave Radiation (OLR) data. The real-time multivariate index (RMM) and the composites of meteorological variables were used, along with the temporal average of the estimated OLR data. All the different patterns for the average period of SACZ showed classic behavior: well-organized and with meteorological variables in phases throughout the troposphere. However, some differences were evident in the organization of each phase of the MJO: at 200 hPa, the Bolivian High (BH) was more flattened during the active phase pattern than in the unfavorable and transition phases, being wider and with a wavier trough embedded in the western flow; at medium levels, the subtropical highs appeared more defined and with a very wide trough; the trough supported the frontal systems on the surface and, together with the subtropical highs, concentrated all the moisture in this layer. In the OLR dataset, the formation of the Coast Squall Line (CSL) occurred during SACZ events in the active phase and MJO transition, whereas in the unfavorable phase, this system was not observed.

Highlights

During austral summer, some atmospheric features are striking, such as anticyclonic circulation at high atmospheric levels in South America (SA), known as the Bolivian High (BH), accompanied by a trough in the vicinity of the northeast region of Brazil (TNB), sometimes with an associated cyclonic vortex
The main objective of this study was to verify the behavior of meteorological variables before, during, and after South Atlantic Convergence Zone (SACZ) events that occur in the active, unfavorable, and transition phases of the Madden–Julian Oscillation (MJO) in SA, along with the spatial variability in Outgoing Longwave Radiation (OLR) resulting from these events and phases
The composites of the days prior (Figure 2a) to the formation of the SACZ shows the predominant presence of BH between 10◦ and 20◦ S and a TNB with the associated vortex over the AO—standard circulation found in the southern hemisphere during the summer [50]

Summary

Introduction

Some atmospheric features are striking, such as anticyclonic circulation at high atmospheric levels in South America (SA), known as the Bolivian High (BH), accompanied by a trough in the vicinity of the northeast region of Brazil (TNB), sometimes with an associated cyclonic vortex. Atlantic Convergence Zone (SACZ) appears as a dominant feature of the South American. BH has been discussed in many studies [1,7,8] as a warm-center anticyclone formed the combination of latent heat release by convective activity in Amazonia and radiative warming from the Bolivian altiplano. The TNB, with the associated cyclonic vortex, has a center of pressure cooler than its periphery and mass convergence in the western sector at low levels [9]. The SACZ is configured by a convergence band oriented in the northwest–

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