The Antecedents of Subtropical PV Streamer Formation in the North Atlantic Basin

Subtropical potential vorticity (PV) streamers are distinct upper-tropospheric troughs that can serve as conduits for tropical-extratropical air mass exchange. This air mass exchange is initiated when anticyclonic Rossby wave breaking (AWB) occurs, where the upstream poleward advection of low PV air folds over the downstream equatorward advection of high PV air, resulting in a positively tilted PV streamer. Frequent occurrence of PV streamer formation in conjunction with AWB can contribute to the time-mean tropical upper tropospheric trough in the North Atlantic (NATL) basin. Once formed, PV streamers can modulate the synoptic-scale environment of the tropical NATL, which may result in changes to climatological tropical cyclogenesis pathways. The intensity spectrum of PV streamers that extend into the subtropical NATL is also related to the strength of the upstream ridge prior to AWB. We hypothesize that stronger upstream ridges occur in conjunction with flanking upstream poleward-directed corridors of enhanced tropical moisture. Greater latent heat release within these enhanced moisture corridors can then promote greater diabatically driven ridge amplification. In turn, these amplified ridges result in more vigorous AWB, which can enable greater positive PV advection into stronger subtropical PV streamers.

This study will investigate different intensity subtropical PV streamers on the 350-K surface in the NATL using the Climate Forecast System Reanalysis. These PV streamers will be linked to their associated AWB events and stratified by intensity, where intensity is objectively defined by their anomalous cumulative PV embedded in the PV streamer after formation. Conditions related to AWB are investigated from lagged composites, which will be used to evaluate how upstream ridge amplification occurs prior to AWB, and how downstream PV streamers form afterward. We will also investigate the climatological variability of PV streamers in the NATL to illustrate variations in intensity, size, and location. These composite and climatological PV streamer characteristics will be illustrated using representative cases.