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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-6
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-6
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Feb 2020

Submitted as: research article | 19 Feb 2020

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This preprint is currently under review for the journal WCD.

Future Meridional Wind Trends Through the Lens of Subseasonal Teleconnections

Dor Sandler and Nili Harnik Dor Sandler and Nili Harnik
  • Geosciences Department, Tel Aviv University, Tel Aviv, Israel

Abstract. Large-scale atmospheric circulation is expected to change dramatically in the upcoming decades, and with it, the interaction between Rossby waves and the jet stream. A common feature of midlatitude wintertime variability is upper tropospheric quasi-stationary number-5 wave packets, which often propagate zonally along the jet. These are collectively referred to as the Circumglobal Teleconnection Pattern (CTP). Their likeness surprisingly emerges as a robust signal in future meridional wind trend projections in the Northern Hemisphere.

We attempt to elucidate this link across timescales, focusing on wave propagation in the jet waveguide in observations and a 36-member ensemble of CMIP5 models. Using EOF analysis on 300 hPa subseasonal V anomalies, we first establish the ensemble's skill in capturing the pattern. Then, by investigating EOF phase space, we characterize the CTP's behavior in present day climatology and how it is projected to change. Under RCP8.5 forcing, most models develop a gradual preference for monthly-mean waves with certain longitudinal phases. The ensemble is thus divided into subgroups based on region of increased wave activity. This categorization strongly corresponds to the ensemble spread in local trend magnitude. Additionally, in two test-case models, this coincides with an increasing number of preferably phased wave packets at the synoptic scale. Some signs suggest that differences in CTP dynamics might stem from mean flow biases, while no evidence was found for the role of tropical diabatic forcing.

Thus, we conclude that this hemisphere-wide climate change signature is actually comprised of several regional effects, partly related to shifts in CTP phase distributions. The strong dynamical disagreement in the ensemble then manifests as significantly different circulation trends, which in turn might affect projected local temperature and precipitation patterns.

Dor Sandler and Nili Harnik

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Dor Sandler and Nili Harnik

Dor Sandler and Nili Harnik

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Latest update: 07 Apr 2020
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Short summary
The Circumglobal Teleconnection Pattern (CTP) is a wavy pattern of wintertime midlatitude subseasonal flow. It is also linked to various extreme weather events. The CTP is predicted to play a prominent role in the future climate. We find that for future projections, most CMIP5 models predict that the CTP will develop a “preferred” phase. Our work establishes that the CTP-like climate change signature is in fact comprised of several regional effects, partly due to shifts in phase distributions.
The Circumglobal Teleconnection Pattern (CTP) is a wavy pattern of wintertime midlatitude...
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