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The role of Rossby wave breaking in the formation and maintenance of tropical-extratropical cloud bands over the South Pacific
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DOI：10.5194/wcd-7-857-2026.png)
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Abstract
En 中文
Abstract. Tropical-extratropical cloud bands are elongated cloud structures bridging tropical and midlatitude regions that act as a primary source of regional precipitation. While the role of Rossby wave breaking in the formation of cloud bands is established; the extent to which this dynamic forcing governs cloud band characteristics; their entire lifecycle; their spatial distribution and seasonality has not yet been systematically quantified. In this study; we apply an object-based approach to reanalysis data to investigate how stratospheric potential vorticity (PV) structures; as indicators of Rossby wave breaking; influence cloud band formation and persistence over the South Pacific region. Our climatological analysis confirms a robust statistical link in which cyclonic PV structures steer tropical moisture poleward and eastward; shaping the diagonal orientation of the cloud bands. We also find that cloud band duration is modulated by the properties of PV structures: long-lived cloud bands are distinguished by a systematically higher frequency of upstream PV structures and are sustained by persistent PV structures throughout their lifecycle; which favour a more zonal orientation of the cloud systems. Categorizing by cloud band duration reveals distinct seasonal regimes: while short-lived events occur year-round; persistent cloud bands are strictly confined to the austral warm season. Furthermore; long-lived cloud bands are associated with PV structures that reside significantly farther equatorward prior to genesis compared to those of short-lived events. These findings highlight that breaking Rossby waves create a tropospheric environment favouring not only the formation but also the maintenance of these cloud bands. Consequently; accurately representing Rossby wave dynamics in weather and climate models is critical for simulating cloud band characteristics and their influence on climate variability.
Keywords:
Rossby wave breaking
tropical-extratropical cloud bands
stratospheric potential vorticity
cloud band lifecycle
South Pacific
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