Intraseasonal and Interannual Mechanisms of Summer Rainfall over Northeast Brazil Using a Hidden Markov Model

A hidden Markov model (HMM) with four hidden states is used to describe the daily precipitation occurrence and wet day intensities of a gridded precipitation dataset over the Northeast Brazil (NEB) for 35 austral summer seasons (1980/81–2014/15). Results show that States 1 and 3 correspond to the wet versus dry conditions associated with the interplay between the Intertropical Convergence Zone (ITCZ) and South American Monsoon System (SAMS). States 2 and 4 feature a southwest-northwest seesaw of precipitation occurrence, associated with antisymmetric conditions between the ITCZ and South Atlantic Convergence Zone (SACZ). The Madden Julian Oscillation (MJO) seems to affect the development of the SACZ in States 3 and 4. In State 4, the MJO influenced the convection in the northwest NEB during phases 8-1-2. During easterly Quasi-Biennial Oscillation (EQBO), the convective activity in the SACZ regions is intensified in States 3 and 4 during MJO phase 1, and weakened in State 4 during phases 1, 3, and 4. In the interannual timescales, States 1 and 3 are preconditioned by a positive and a negative South Atlantic Ocean Dipole (SAOD), respectively. State 2 is modulated by a long and positive El Niño-Southern Oscillation (ENSO) that triggered extratropical teleconnection patterns in both hemispheres. State 4 is preconditioned by a negative ENSO that produces changes in the Walker and Hadley circulations. These findings enhance the understanding of the dynamic processes of summer rainfall over the NEB and their association with potentially predictable intraseasonal and interannual teleconnections on seasonal timescales.