Intensity Variations and Environmental Impact of Subtropical North Atlantic Basin PV Streamers

Subtropical potential vorticity (PV) streamers are elongated filaments of high PV air that can serve as conduits for tropical-extratropical air mass exchange. These PV streamers often originate from anticyclonic Rossby wave breaking (AWB), where upstream low PV air is advected poleward over downstream high PV air in the upper troposphere. This flow evolution results in an elongated, positively tilted PV streamer that also represents a distinct upper-tropospheric trough that modifies the nearby environment. Frequent occurrence of PV streamer formation in conjunction with AWB contributes to the climatologically observed mid-ocean trough (MOT) in the subtropical North Atlantic (NATL) basin, where MOTs govern climatological corridors of environmental high vertical wind shear (VWS), low upper-tropospheric thickness, suppressed extratropical moisture upstream, and enhanced tropical moisture downstream. These environmental flow modifications ultimately impact the frequency of trough-induced extreme precipitation over the Greater Antilles as well as the frequency of tropical cyclogenesis in the NATL basin. An important question this study will address is how these environmental flow reconfigurations are impacted by different intensity subtropical PV streamers, where stronger PV streamers are hypothesized to have greater VWS, more anomalous moisture corridors, and be associated with more robust upstream ridge growth than weaker PV streamers. 

PV streamers are identified from combining prior methodologies in order to link meridional gradient reversals in 350 K PV (defining AWB) to elongated filaments of high PV (defining a PV streamer) using Climate Forecast System Reanalysis data. PV streamer intensity is calculated as a standardized PV anomaly relative to climatology, and the top and bottom 20% of the cumulative intensity distribution of PV streamers will be categorized as the strongest and weakest PV streamers. Composites of these PV streamer categories will be constructed to evaluate how VWS, thickness, and moisture are altered by differences in PV streamer intensity. Finally, these PV streamer categories will be time-lagged before their development to illustrate differences in upstream ridging between the strong and weak PV streamer categories.