Moisture Characteristics Distinguishing Transformed From Non‐Transformed Mixed Rossby‐Gravity Waves Over the Western North Pacific

Abstract Mixed Rossby‐gravity (MRG) waves are essential synoptic‐scale variability in the equatorial atmosphere. This study investigates the role of moisture variation in the transition of MRG waves to tropical depression (TD)‐type waves in the western North Pacific. Using ERA5 reanalysis data, an identification algorithm based on the theoretical solution and the K‐means clustering method, MRG wave events were separated into transformed (MRG‐TD) and non‐transformed (MRG) types. Before transforming into a TD‐type disturbance, the MRG waves in the MRG‐TD type exhibit stronger moisture anomalies and embedded convection compared to the MRG type, which favors intensification and the genesis of TD‐type disturbance. Enhanced convection and moisture anomalies caused by a more pronounced anomalous meridional wind are located relatively northward in MRG‐TD type. These northward enhanced humidification facilitates the poleward shifting of the convection and coupled circulation. The background environment also contributes to the observed differences in moisture budgets between these types, with enhanced background moisture exhibited in the lower‐to‐mid troposphere with stronger background ascending motion in the equatorial North Pacific. These findings provide insights into the coupling between moisture, convection, and dynamics of the MRG‐TD transition.