A Moisture Mode and Tropical Wave Analysis of Counterintuitive MJO Events

Abstract Recent studies have analyzed the Madden–Julian oscillation (MJO) as a moisture mode over the Indian Ocean region where MJO convection is driven by moisture anomalies. Specifically, the distribution of moist entropy (ME) tendency with negative anomalies to the west of the convective center and positive anomalies to the east is an important factor in MJO propagation. Nonetheless, some MJO events terminate despite being associated with a downstream environment that is becoming more favorable based on ME tendency. This study builds and investigates a climatology of counterintuitive MJOs, i.e., events that behave differently from expectation, based on classifications stemming from the moisture mode framework. The ME tendency east of the convective center and associated budget revealed that counterintuitive continuing events have downstream environments that become more hostile due to negative contributions from longwave radiation and latent heat fluxes that nearly balance positive contributions from the advective terms. Meanwhile, counterintuitive terminating events have environments that become more favorable due to lower magnitude negative contributions from the same terms despite similar positive contributions from advection. The real-time multivariate MJO (RMM) index amplitude and total anomalous ME were used to observe connections between MJO strength and counterintuitive events. Both metrics were unable to discriminate between events that behave similarly, given different evolving downstream environments or events with different outcomes but similarly evolving environments. Tropical wave activity was also analyzed using multiple variables, and higher local power in westward wave activity was observed for events that terminate with higher power in eastward wave modes for continuing events.