Atmospheric and oceanic mechanisms in precipitation in March 2018 in Ceará, Brazil

Abstract

This study analyzes the atmospheric and oceanic mechanisms that influenced rainfall distribution in Ceará, Brazil during the 2018 rainy season and the impacts of the observed rainfall distribution on agriculture in the region. Special attention is given to the month of March, when precipitation was below the climatological average. Precipitation, wind, omega, specific humidity, outgoing longwave radiation, and oceanic indices from the Pacific and Atlantic data were used in the analyses. The Multivariate Real-Time Madden–Julian Oscillation (MJO) Index was employed to assess the influence of the MJO on precipitation in March 2018. The results indicate that subseasonal variability, through the MJO in phases 4, 5, and 6, played a crucial role in suppressing convective activity. Additionally, a delayed austral summer pattern was found, with the South American Convergence Zone (SACZ) positioned further north and a quasi-stationary trough at altitude. These two atmospheric factors inhibited the more intense rainfall activity in the Intertropical Convergence Zone (ITCZ). In the ocean analyses, Sea Surface Temperature (SST) anomalies indicated the presence of La Niña in the equatorial Pacific, although it was in transition from cooling to warming. This, in addition to the neutrality of the interhemispheric gradient of the Tropical Atlantic SST anomalies, may have also contributed to negative precipitation anomalies and influenced the MJO displacement. MJO phases associated with suppression contributed to economic losses for the agricultural sector.