Dissertation Defense
Luis Andrés Rodríguez Flores
Program: Meteorology
Title: "Atmospheric Structure in Normal Modes during the 2013/2014 Summer Drought in Southeastern Brazil"
Advisor: Prof. Dr. Pedro Leite da Silva Dias - IAG/USP
Judging Committee:
- Prof. Dr. Pedro Leite da Silva Dias – Presidente e Orientador - IAG/USP
- Dr. Enver Manuel Amador Ramirez Gutierrez – INPE
- Profa. Dra. Alice Marlene Grimm – UFPR
Alternate Members:
- Prof. Dr. Carlos Frederico Mendonça Raupp - IAG/USP
- Prof. Dr. Tercio Ambrizzi - IAG/USP
- Dr. Caio Augusto dos Santos Coelho – INPE
- Profa. Dra. Ilana Elazari Klein Coaracy Wainer - IO/USP
- Profa. Dra. Michelle Simões Reboita – UNIFEI
Abstract: This study conducted an in-depth dynamic analysis of the extreme drought that affected the Southeast of Brazil during the austral summer of 2013/2014, using the methodology of three-dimensional normal mode decomposition of the atmosphere. The study integrated ERA-5 reanalysis data and precipitation observations from the GPM satellite (IMERG) to examine the vertical and horizontal structure of the atmospheric systems involved during the event. From a synoptic perspective, the study confirms several results already published in other articles. This drought was characterized by an atmospheric blocking system of an almost barotropic nature over the South Atlantic. This pattern consistently inhibited the formation of the South Atlantic Convergence Zone (SACZ) and diverted frontal systems to more southern latitudes. The modal analysis revealed that this blocking was sustained by a planetary-scale Rossby wave train, excited by persistent convection in the Western Pacific and propagated through the subtropical jet waveguide. The normal mode decomposition allowed for the quantification of the specific contribution of different wave types: Rossby waves showed maximum energy in barotropic modes (m=1-3), while Kelvin waves and inertial gravity waves (EIG/WIG) showed a predominant energy signature in baroclinic modes (m=7-9). A significant contribution from the stratosphere to the energy of the upper baroclinic modes was also detected, particularly over tropical regions. The study identified three distinct phases of the event (ET1, ET2, ET3), with the critical phase (ET2) presenting the highest modal energy values and the most defined blocking configuration. Spectral analysis showed energy concentration in the first zonal modes (k=1-4), confirming the large-scale nature of the event. It is concluded that the 2013/2014 drought resulted from the synergistic interaction between remote tropical forcings, Rossby wave-mediated teleconnections, the establishment of persistent atmospheric blocking, and energy transfer between vertical modes. The modal approach proved to be a powerful tool for diagnosing extreme events, offering valuable insights for improving seasonal climate predictability in the region.
Keywords: extreme drought; etmospheric normal modes; etmospheric waves; etmospheric blocking