Influence of the Madden–Julian Oscillation and Caribbean Low-Level Jet on East Pacific Easterly Wave Dynamics

The east Pacific warm pool in which easterly waves (EWs) exist exhibits basic state variability associated with the Madden-Julian Oscillation (MJO) and Caribbean Low-Level Jet (CLLJ). This study compares and contrasts composite changes in the background environment, eddy kinetic energy EKE budgets, moisture budgets, and EW tracks during MJO and CLLJ events. While previous studies have shown that the MJO influences jet activity in the east Pacific, the influence of the MJO and CLLJ on EWs is not synonymous. The MJO and CLLJ have similar influences along the Central American coast in the northeastern portion of the basin while the MJO has a more expansive westward reach from the coast. The CLLJ is a stronger modulator of the ITCZ than the MJO. Anomalous low-level westerly MJO and CLLJ periods are associated with favorable conditions for EW development along the main EW path paralleling the Central American coast, contrary to previous findings about the relationship of the CLLJ to EWs. Easterly MJO and CLLJ periods support enhanced EW development along the ITCZ, although the CLLJ is a greater modulator of EW tracks in this region, likely associated with stronger changes to the background state and their influence on the EKE budget. EW growth in the ITCZ during easterly MJO periods is more reliant on barotropic conversion as an energy source than for strong CLLJ period waves, when EAPE to EKE conversion associated with ITCZ convection is more important. A moisture budget analysis for ITCZ waves shows that strong CLLJ period waves have stronger horizontal advection in front of the wave axis relative to easterly MJO periods waves. These differences in horizontal advection are interpreted in the context of a linearized horizontal advection budget. Thus, the influence of these phenomena on east Pacific EWs should be considered distinct.