Influence of the Madden-Julian Oscillation on moisture transport by the Caribbean Low Level Jet during the Midsummer Drought in Mexico

Abstract

Abstract This study aims to improve the understanding of the role of the Madden-Julian Oscillation (MJO) in modulating the midsummer drought (MSD) in Mexico. First, the main moisture sources for the MSD region in Mexico during the summer were identified using the Lagrangian particle dispersion model FLEXPART for the period 1979–2017. From this analysis, the Caribbean Sea was identified as one of the main moisture sources, particularly the area where the core of the Caribbean low-level jet (CLLJ) is located. Second, the water vapour flux transported by the CLLJ to Mexico was then analysed. It was found that the summer seasonal cycle of the CLLJ is associated with the bimodal precipitation pattern in Mexico through the seasonal variability of the moisture contribution from the CLLJ to precipitation over the MSD region, thereby confirming the CLLJ as a key element in the occurrence of the MSD in the Americas. Third, the influence of the MJO on this transport was examined. This analysis showed that the locally dry phases of the MJO decrease the contribution of moisture from the CLLJ core towards the MSD region, while the locally wet phases increase it. Moreover, phases 1 and 2 of the MJO were found to influence the first precipitation peak that occurs in the southwestern region of Mexico by increasing the contribution of moisture from the northeastern tropical Pacific. The study ends by proposing, for the first time, a mechanism by which the MJO modulates the MSD in Mexico.