The Pacific decadal oscillation as a modulator of summertime North Atlantic Rossby wave breaking

Abstract

Investigation into the Pacific decadal oscillation’s (PDO’s) role in modulating the intra-basin frequency of North Atlantic Rossby wave breaking (RWB) is carried out utilizing the Community Earth System Model (CESM). Several 15-year simulations are run with the model, each using a unique set of prescribed sea surface temperatures (SSTs) corresponding to different phases and configurations of the PDO regressed on all 12 months of the climatological SSTs. Potential vorticity (PV) maps on the 200 hPa isobaric surface are used to detect anticyclonic RWB events. Results suggest that when the PDO is in its positive (negative) phase, a greater number of anticyclonic RWB events are recorded in the eastern (western) half of the North Atlantic. Additionally, PDO negative regimes are shown to drive more robust intra-basin RWB frequency changes than PDO positive regimes. Analysis of the large-scale circulation and synoptic environment changes imposed by the SST anomalies of each simulation reveals different pathways for Rossby wave train (RWT) development that, in turn, affect North Atlantic RWB statistics. When the PDO signals are divided into different components, the largest changes in RWB statistics are shown to occur whenever positive SST anomalies are present in the North Pacific, as these serve as fuel for high frequency RWT development and more dramatic changes to North Atlantic RWB statistics. Furthermore, the role of atmospheric preconditioning to RWB is explored and uncovered to considerably affect RWB statistics. Results from this study reaffirm the important role played by positive SST anomalies as year-round drivers of teleconnection patterns and inter-basin interactions.