The Intrinsic 150‐Day Periodicity of the Southern Hemisphere Extratropical Large‐Scale Atmospheric Circulation

Journal Article · Wed May 31 00:00:00 UTC 2023 · AGU Advances

DOI:https://doi.org/10.1029/2022AV000833· OSTI ID:1975903

Lubis, Sandro W. ^[1]; Hassanzadeh, Pedram ^[2]

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1. Rice University Houston TX USA, Pacific Northwest National Laboratory Richland WA USA
2. Rice University Houston TX USA

Abstract

The variability of the Southern Hemisphere (SH) extratropical large‐scale circulation is dominated by the Southern Annular Mode (SAM), whose timescale is extensively used as a key metric in evaluating state‐of‐the‐art climate models. Past observational and theoretical studies suggest that the SAM lacks any internally generated (intrinsic) periodicity. Here, we show, using observations and a climate model hierarchy, that the SAM has an intrinsic 150‐day periodicity. This periodicity is robustly detectable in the power spectra and principal oscillation patterns (aka dynamical mode decomposition) of the zonal‐mean circulation, and in hemispheric‐scale precipitation and ocean surface wind stress. The 150‐day period is consistent with the predictions of a new reduced‐order model for the SAM, which suggests that this periodicity is associated with a complex interaction of turbulent eddies and zonal wind anomalies, as the latter propagate from low to high latitudes. These findings present a rare example of periodic oscillations arising from the internal dynamics of the extratropical turbulent circulations. Based on these findings, we further propose a new metric for evaluating climate models, and show that some of the previously reported shortcomings and improvements in simulating SAM's variability connect to the models' ability in reproducing this periodicity. We argue that this periodicity should be considered in evaluating climate models and understanding the past, current, and projected Southern Hemisphere climate variability.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: National Science Foundation (NSF); Office of Naval Research (ONR); USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1975903
• Alternate ID(s): OSTI ID: 1983706; OSTI ID: 1994563
• Report Number(s): PNNL-SA--179277; e2022AV000833
• Journal Information: AGU Advances, Journal Name: AGU Advances Journal Issue: 3 Vol. 4; ISSN 2576-604X
• Publisher: American Geophysical Union (AGU)
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
climate model evaluation
dynamic mode decomposition
eddy-mean flow interaction
periodic oscillation
propagating annular modes
southern annular mode