Bimodality of hemispheric winter atmospheric variability via average flow tendencies and kernel EOFs

The topic of the existence of planetary winter circulation regimes has gone through a long debate. This article contributes to this debate by investigating nonlinearity in a 3-level quasi-geostrophic model and the Japanese JRA-55 reanalysis. The method uses averaged flow tendencies and kernel princi...

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Bibliographic Details
Published in:Tellus. Series A, Dynamic meteorology and oceanography Dynamic meteorology and oceanography, 2019, Vol.71 (1), p.1633847
Main Authors: Hannachi, A., Iqbal, W.
Format: Article
Language:English
Subjects:
Atmospheric forcing
Average flow
bimodality
Climate change
Dynamic height
kernel EOFs
large scale flow
Nonlinearity
Ocean-atmosphere system
Oscillations
Probability theory
Sea level
Sea level pressure
Winter
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Summary:The topic of the existence of planetary winter circulation regimes has gone through a long debate. This article contributes to this debate by investigating nonlinearity in a 3-level quasi-geostrophic model and the Japanese JRA-55 reanalysis. The method uses averaged flow tendencies and kernel principal component (PC) analysis. Within two-dimensional (2D) kernel PCs the model reveals two fixed (or stationary) points. The probability density function (PDF) within this space is strongly bimodal where the modes match the regions of low tendencies in consistency with low-order conceptual models. The circulation regimes represent respectively zonal and blocked flows. Application to daily winter northern hemisphere sea level pressure and 500-hPa geopotential height yields strong bimodal PDFs. The modes represent respectively polar highs and lows with signatures of North Atlantic Oscillation. A clear climate change signal is observed showing a clear reduction (increase) of occurrence probability of polar high (low), translating into an increase of probability of zonal flow. Relation of the climate change signal to the polar amplification hypothesis is discussed.
ISSN:1600-0870
0280-6495
1600-0870
DOI:10.1080/16000870.2019.1633847