Graphs from the paper
The normalized power spectra of the SAM’s zonal index (solid black lines) with a 90% confidence interval (grey shading) in both (a) the reanalysis data and (b) a comprehensive global climate model shows a clear 150-day peak as predicted from theory (red line). This peak exists in (c) an idealized model with propagating regime but is absent in (d) a model with non-propagating regime. The red-noise spectra are indicated by the solid blue lines. Credit: Lubis and Hassanzadeh [2023], Figure 1
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

The variability of the Southern Hemisphere large-scale atmospheric circulation is dominated by hemispheric-scale north-south fluctuations of the midlatitude jet stream, known as the Southern Annular Mode (SAM). Understanding the dynamics of SAM is of fundamental importance because of its significant impacts on the Southern Hemisphere weather and climate.

Using theory, reanalysis data, and a model hierarchy, Lubis and Hassanzadeh [2023] identify a new intrinsic mode of atmospheric variability, the 150-day periodicity in SAM. The periodicity is associated with a propagating regime in the SAM that arises from the interaction between the two leading modes of the zonal-mean zonal winds. Hence, unlike many other periodic oscillations in the climate system, this newly identified periodicity is internally generated within the extratropical atmosphere. A new metric based on this periodicity is introduced to quantitatively evaluate the climate models. How this periodicity might change under anthropogenic climate change is a topic for future work.

Citation: Lubis, S. W., & Hassanzadeh, P. (2023). The intrinsic 150-day periodicity of the Southern Hemisphere extratropical large-scale atmospheric circulation. AGU Advances, 4, e2022AV000833. https://doi.org/10.1029/2022AV000833

—Sarah Kang, Editor, AGU Advances

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