Synoptic variability in the moist margin and its connection to tropical and extratropical weather systems

The moist margin is a sharp gradient of humidity that separates the moist deep tropics from the drier subtropics, and as such its movement is important for describing rainfall variability. In this work, we investigate how weather systems are related to synoptic variability in the moist margin. We use an object-based approach to relate moist margin perturbations to convectively coupled equatorial waves, the Madden-Julian Oscillation (MJO) and monsoon low-pressure systems (LPS). We also consider extratropical interactions with the moist margin, which are defined through upper-level potential vorticity (PV) anomalies. The results indicate that the MJO and equatorial Rossby waves have significant modulating effects on the moist margin. In comparison, monsoon LPS are infrequent but strongly influence the moist margin when they occur. The largest and longest-lived perturbations are commonly related to PV anomalies, and their composite structure reveals a clear wave-like signal, often with anticyclonic PV anomalies near the perturbed margin and cyclonic PV anomalies remotely. Open questions remain regarding the potential two-way interactions and feedback mechanisms between extratropical PV anomalies and the moist margin, which are examined here in some detail.