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Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2012 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 38, no 5-6, 1249-1262 p.Article in journal (Refereed) Published
Abstract [en]

This study examines the mutual interaction between topographically-forced atmospheric stationary waves and continental-scale ice sheets using a thermomechanical ice-sheet model coupled to a linear as well as a fully-nonlinear dry atmospheric primitive equation model. The focus is on how the stationary-wave induced ablation feeds back on the ice sheet. Simulations are conducted in which an embryonal ice mass, on an idealised “North American” continent, evolves to an equilibrium ice sheet. Under the coupling to the linear atmospheric model, the equilibrium ice sheet is primarily controlled by the ratio between the wavelength of the stationary waves and the zonal continental extent. When this ratio is near two, the ice sheet has its center of mass shifted far eastward and its shape is broadly reminiscent of the Laurentide ice sheet at LGM. For wavelengths comparable to the continental extent, however, the ice margin extends far equatorward on the central continent but is displaced poleward near the eastern coast. Remarkably, the coupling to the nonlinear atmospheric model yields equilibrium ice sheets that are virtually identical to the ones obtained in uncoupled simulations, i.e. a symmetric ice sheet with a zonal southern margin. Thus, the degree of linearity of the atmospheric response should control to what extent topographically-forced stationary waves can reorganise the structure of ice sheets. If the stationary-wave response is linear, the present results suggest that spatial reconstructions of past ice sheets can provide some information on the zonal-mean atmospheric circulation that prevailed.

Place, publisher, year, edition, pages
2012. Vol. 38, no 5-6, 1249-1262 p.
Keyword [en]
Stationary waves, ice sheets, flow-induced ablation, nonlinear topographic wave response, Laurentide ice sheet
National Category
Meteorology and Atmospheric Sciences Climate Research
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-55550DOI: 10.1007/s00382-011-1004-6ISI: 000302245900025OAI: oai:DiVA.org:su-55550DiVA: diva2:405092
Available from: 2011-03-21 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
In thesis
1. The mutual interaction between the time-mean atmospheric circulation and continental-scale ice sheets
Open this publication in new window or tab >>The mutual interaction between the time-mean atmospheric circulation and continental-scale ice sheets
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Geomorphological evidence of glaciations exist for the Last Glacial Maximum (about 20 kyr ago). At this time, both North America and Eurasia were covered by extensive ice sheets which are both absent today. However, the temporal and spatial evolution of the ice sheets from the previous interglacial up to the fully-glaciated conditions at LGM is still unresolved and remains a vexing question in climate dynamics.

The evolution of ice sheets is essentially controlled by the prevailing climate conditions. On glacial time-scales, the climate is shaped the by the orbital variations of the Earth, but also by internal feedbacks within the climate system. In particular, the ice sheets themselves have the potential to change the climate within they evolve. This thesis focuses on the interactions between ice sheets and the time-mean atmospheric circulation (stationary waves). It is studied how the stationary waves, which are forced by the ice-sheet topography, influence ice-sheet evolution through changing the near-surface air temperature.

In this thesis, it is shown that the degree of linearity of the atmospheric response controls to what extent the stationary waves can reorganise the structure of ice sheet. Provided that the response is linear, the stationary waves constitute a leading-order feedback, which serves to increase the volume and deform the shape of ice sheets. If the stationary-wave response to ice-sheet topography is nonlinear in character, the impact on the ice-sheet evolution tends to be weak. However, it is further shown that the amplitude of the nonlinear topographical response, and hence its effect on the ice-sheet evolution, can be significantly enhanced if thermal cooling over the ice sheets is taken into account.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2011. 35 p.
Keyword
Atmospheric stationary waves, Paleo ice sheets, Ice-sheet ablation, Atmosphere-ice sheet modelling
National Category
Climate Research Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-55931 (URN)978-91-7447-271-4 (ISBN)
Public defence
2011-04-29, Högbomsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Submitted. Available from: 2011-04-07 Created: 2011-03-30 Last updated: 2011-04-01Bibliographically approved
2. On the interaction between ice sheets and the large-scale atmospheric circulation over the last glacial cycle
Open this publication in new window or tab >>On the interaction between ice sheets and the large-scale atmospheric circulation over the last glacial cycle
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The last glacial cycle (c. 115-12 kyr BP) was the most recent in a series of recurring glaciations of the subpolar continents. Massive ice sheets evolved in Eurasia and North America, which, at their maximum, were of continental scale and together lowered the global sea-level by approximately 100 m. The paleo-modelling community has focused on the last glacial maximum (LGM, ~ 20 kyr BP), leaving the longer period when the ice sheets evolved to their LGM configurations largely unexplored.

In this thesis we study the mutual interaction between the time-mean atmospheric circulation and the evolution of the Northern Hemisphere ice sheets over the build-up phase of the last glacial cycle. Experiments are conducted with coupled atmosphere-ice-sheet models and a circulation model forced by geologically consistent reconstructions of the ice-sheet topography at key stages of the glacial cycle.

The main findings from these studies are that the ice evolution in North America may have been controlled by circulation anomalies induced by the background topography in conjunction with the ice sheets themselves. A geologically consistent pre-LGM ice sheet could only be obtained when including the North American Cordillera. However, the ice sheets' influence on the local climate conditions is also found to be paramount for this configuration. We further suggest that the incipient ice sheets may have had a limited influence on the large-scale winter circulation as a result of their location relative the westerly mean flow. The LGM Laurentide Ice Sheet (LIS) was, however, different because of its continent-wide extent, and it may therefore have had a large influence on the planetary-scale circulation, especially in the Atlantic sector. We find that the planetary waves forced by the LIS were considerably larger than at earlier times, and, as a result of a more frequent planetary wave reflection over the Atlantic Ocean basin, an altered stationary wave field and a zonalised winter jet.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2014. 49 p.
Keyword
Atmospheric stationary waves, coupled atmosphere-ice sheet modelling, stationary wave-ice sheet interactions
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-107925 (URN)978-91-7649-010-5 (ISBN)
Public defence
2014-11-11, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.

Available from: 2014-10-20 Created: 2014-10-03 Last updated: 2014-11-18Bibliographically approved

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