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Bimodality of hemispheric winter atmospheric variability via average flow tendencies and kernel EOFs
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology . Finish Meteorological Institute, Finland.
Number of Authors: 22019 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 71, no 1, article id 1633847Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2019. Vol. 71, no 1, article id 1633847
Keywords [en]
large scale flow, bimodality, kernel EOFs, climate change
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-170781DOI: 10.1080/16000870.2019.1633847ISI: 000473733900001OAI: oai:DiVA.org:su-170781DiVA, id: diva2:1338371
Available from: 2019-07-22 Created: 2019-07-22 Last updated: 2019-07-22Bibliographically approved

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Hannachi, AbdelwahebIqbal, Waheed
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