The Pacific decadal oscillation as a modulator of summertime North Atlantic Rossby wave breaking
- PDF / 3,976,574 Bytes
- 19 Pages / 595.276 x 790.866 pts Page_size
- 38 Downloads / 170 Views
The Pacific decadal oscillation as a modulator of summertime North Atlantic Rossby wave breaking Breanna L. Zavadoff1 · Ben P. Kirtman1 Received: 28 March 2020 / Accepted: 2 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
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. Keywords Rossby wave breaking · Pacific decadal oscillation · Rossby wave train · Atmospheric preconditioning
1 Introduction Over the past few decades, Rossby wave breaking (RWB) in the upper troposphere/lower stratosphere has been extensively studied due to its wide ranging impacts on regional and large-scale weather events. First identified by McIntyre and Palmer (1983, 1984), RWB is described as the “rapid and irreversible deformation of potential vorticity (PV) contours on isentropic surfaces” and is characterized by a quasi-horizontal mixing of stratospheric and tropospheric air (Holton et al. 1995; Scott and Cammas 2002). Breaking occurs when Rossby waves encounter critical lines in regions * Breanna L. Zavadoff [email protected] Ben P. Kirtman [email protected] 1
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA
of weak time-mean winds and/or reach a threshold amplitude, which forces a nonlinear transformation of ambient PV contours into a meridionally elongated, zonally confined pattern (McIntyre and Palmer 1983; Thorncrof
Data Loading...
