North Atlantic Eddy-Driven Jet in interglacial and glacial winter climates

Merz, Niklaus; Raible, Christoph; Woollings, Tim (2015). North Atlantic Eddy-Driven Jet in interglacial and glacial winter climates. Journal of Climate, 28(10), pp. 3977-3997. American Meteorological Society 10.1175/JCLI-D-14-00525.1

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The atmospheric westerly flow in the North Atlantic (NA) sector is dominated by atmospheric waves or eddies generating via momentum flux convergence, the so-called eddy-driven jet. The position of this jet is variable and shows for the present-day winter climate three preferred latitudinal states: a northern, central, and southernposition in the NA. Here, the authors analyze the behavior of the eddy-driven jet under different glacial and interglacial boundary conditions using atmosphere–land-only simulations with the CCSM4 climate model. As state-of-the-art climate models tend to underestimate the trimodality of the jet latitude, the authors apply a bias correction and successfully extract the trimodal behavior of the jet within CCSM4. The analysis shows that during interglacial times (i.e., the early Holocene and the Eemian) the preferred jet positions are rather stable and the observed multimodality is the typical interglacial character of the jet. During glacial times, the jet is strongly enhanced, its position is shifted southward, and the trimodal behavior vanishes. This is mainly due to the presence of the Laurentide ice sheet (LIS). The LIS enhances stationary waves downstream, thereby accelerating and displacing the NA eddy-driven jet by anomalous stationary momentum flux convergence. Additionally, changes in the transient eddy activity caused by topography changes as well as other glacial boundary conditions lead to an acceleration of the westerly winds over the southern NA at the expenseof more northernareas. Consequently, bothstationaryand transient eddiesfoster the southward shift of the NA eddy-driven jet during glacial winter times.

Item Type:

Journal Article (Original Article)

Division/Institute:

10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Physics Institute > Climate and Environmental Physics
08 Faculty of Science > Physics Institute

UniBE Contributor:

Merz, Niklaus and Raible, Christoph

Subjects:

500 Science > 530 Physics
500 Science > 550 Earth sciences & geology

ISSN:

0894-8755

Publisher:

American Meteorological Society

Language:

English

Submitter:

Monika Wälti-Stampfli

Date Deposited:

04 Jun 2015 16:19

Last Modified:

16 Nov 2015 02:30

Publisher DOI:

10.1175/JCLI-D-14-00525.1

BORIS DOI:

10.7892/boris.69027

URI:

https://boris.unibe.ch/id/eprint/69027

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