Banca de QUALIFICAÇÃO: ISAMARA DE MENDONÇA SILVA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : ISAMARA DE MENDONÇA SILVA
DATE: 26/09/2022
TIME: 09:00
LOCAL: AUDITORIO DO CCET
TITLE:

INTRASAZONAL AND INTER-ANNUAL MECHANISMS OF RAIN OCCURRENCE IN NORTHEASTERN BRAZIL USING MARKOV'S HIDDEN MODEL

KEY WORDS:

Northeast of Brazil; Precipitation occurrence; Hidden Markov model; Madden Julian Oscillation; El Niño-Southern Oscillation; Teleconnection patterns 

PAGES: 65
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Meteorologia
SPECIALTY: Climatologia
SUMMARY:

The rainfall over the Northeast Brazil presents a large climate variability and is highly seasonal and intrinsically conditioned to changes in the large-scale atmospheric circulation. A large part of this climate variability is due to teleconnection patterns, such that the perception of dynamic processes of precipitation and the influence of teleconnection patterns becomes important for the study and understanding of the climate of the Northeast Brazil. This work aims to employ the hidden Markov model to describe the occurrence and intensity of daily precipitation over Northeast Brazil for summer, autumn, winter, and spring. Thus, a diagnostic analysis is performed to characterize the large-scale atmospheric circulation for the hidden states in each season separately. Subsequently, the teleconnection patterns of the hidden states are described for the intraseasonal and interannual timescales. A rainfall database interpolated in a regular grid of 0.25°×0.25° longitude/latitude is used to estimate the parameters of the model during the period from 1980 to 2015. The reanalysis data are used to build the atmospheric and oceanic maps. The Bayesian Information Criterion is applied to assess the fit of model concerning the number of hidden states and then generate the most likely daily sequence of hidden states for each season. The results for the summer indicate a hidden Markov model with four hidden states describing the occurrence and intensity of daily precipitation over Northeast Brazil. In this case, states 1 and 3 correspond to wet versus dry conditions associated with the interplays between the Intertropical Convergence Zone and the South American Monsoon System. States 2 and 4 show a southwest-northwest seesaw pattern of precipitation occurrence, related to antisymmetric conditions between the Intertropical Convergence Zone and the South Atlantic Convergence Zone. On the intraseasonal time scale, the influence of the Madden-Julian Oscillation on states differs in intensity but not in the propagation phase. The Madden-Julian Oscillation modulates convective activity over Northeast Brazil, intensifying (suppressing) convection during the wet (dry) phases of this oscillation. On the interannual time scale, state 1 is preconditioned by the positive phase of the South Atlantic Ocean Dipole, which forms as a response to the positive phase of the Antarctic Oscillation. The El Niño-Southern Oscillation preconditions the other states in the Pacific, where states 2 and 3 are associated with the warm phase and state 4 is related to the cold phase. Teleconnection patterns occur via the tropics in state 3. State 2 (State 4) is associated with the positive (negative) phase of Pacific-North America and the first (second) mode of Pacific-South America. All these teleconnection mechanisms can alter the large-scale atmospheric circulation and, consequently, modulate the Intertropical Convergence Zone, the South American Monsoon System, and the South Atlantic Convergence Zone, affecting the occurrence and intensity of precipitation in the summer over Northeast Brazil. These results improve the understanding of the dynamic processes of summer rainfall over Northeast Brazil and their association with potentially predictable intraseasonal and interannual teleconnection patterns on seasonal time scales. It is expected that the hidden Markov model will also select distinct rainfall states during autumn, winter, and spring, which characterize the occurrence and intensity of precipitation over Northeast Brazil.

COMMITTEE MEMBERS:
Presidente - 1858120 - DAVID MENDES
Interno - 1164414 - WEBER ANDRADE GONCALVES
Externo ao Programa - 2352793 - DEUSDEDIT MONTEIRO MEDEIROS - UFRNExterna à Instituição - MEIRY SAYURI SAKAMOTO - FUNCEME