The distinct influence of two Madden-Julian’s trajectory classes on the South American Dipole

The South American Dipole (SAD) is the main mode of rainfall variability at the
intrasesasonal time-scale in South America. Its phases, determined by wet/dry conditions over the SACZ and SESA regions, have been related to extreme precipitation and droughts across South America, but are yet to be fully understood and predicted. In this work, we study the intraseasonal predictability of the SAD in relation with the Madden-Julian Oscillation (MJO) in the DJFM
season. We show that significant predictability windows for the SAD’s extreme states emerge up to 10-20 days after the MJO is found in phase 2. In particular, we introduce a classification of MJO trajectories based on the 𝑅𝑀𝑀 index, defining Long and Intense (𝐿 𝐼𝑇) and Not Long and Intense (𝑁 𝐿 𝐼𝑇) sets of trajectories. These sets bear resemblance to MJO events that are able or unable to propagate beyond the Maritime Continent, respectively. Moreover, we show that they influence differently over the SAD’s predictability. While both sets present similar tropical extratropical teleconnections, the 𝐿 𝐼𝑇 set presents a more intense and persistence tropical-tropical teleconnection. Because of this, there is a set-independent predictability for the SESA region, influenced by both tropical and extratropical teleconnections, and a 𝐿 𝐼𝑇 dependency for the SACZ
predictability, influenced mainly by the presence of the tropical-tropical teleconnection. Overall, our work contributes to the intraseasonal predictability of SAD phases and understanding its relationship with MJO events.