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The mutual interaction between the time-mean atmospheric circulation and continental-scale ice sheets
Stockholm University, Faculty of Science, Department of Meteorology .
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 [en]
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: urn:nbn:se:su:diva-55931ISBN: 978-91-7447-271-4OAI: oai:DiVA.org:su-55931DiVA: diva2:407438
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
List of papers
1. The impact of topographically forced stationary waves on local ice-sheet climate
Open this publication in new window or tab >>The impact of topographically forced stationary waves on local ice-sheet climate
2010 (English)In: Journal of Glaciology, ISSN 0022-1430, Vol. 56, no 197, 534-544 p.Article in journal (Refereed) Published
Abstract [en]

A linear two-level atmospheric model is employed to study the influence of ice-sheet topography on atmospheric stationary waves. In particular, the stationary-wave-induced temperature anomaly is considered locally over a single ice-sheet topography, which is computed using the plastic approximation. It is found that stationary waves induce a local cooling which increases linearly with the ice volume for ice sheets of horizontal extents smaller than 1400 km. Beyond this horizontal scale, the dependence of stationary-wave-induced cooling on the ice volume becomes gradually weaker. For a certain ice-sheet size, and for small changes of the surface zonal wind, it is further shown that the strength of the local stationary-wave-induced cooling is proportional to the basic state meridional temperature gradient multiplied by the vertical stratification in the atmosphere. These results are of importance for the nature of the feedback between ice sheets and stationary waves, and may also serve as a basis for parameterizing this feedback in ice-sheet model simulations (e.g. through the Pleistocene glacial/interglacial cycles).

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:su:diva-49151 (URN)10.3189/002214310792447824 (DOI)000280930000014 ()
Note
authorCount :2Available from: 2010-12-10 Created: 2010-12-10 Last updated: 2011-03-30Bibliographically approved
2. Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response
Open this publication in new window or tab >>Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response
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.

Keyword
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:nbn:se:su:diva-55550 (URN)10.1007/s00382-011-1004-6 (DOI)000302245900025 ()
Available from: 2011-03-21 Created: 2011-03-21 Last updated: 2014-10-06Bibliographically approved
3. Interactions between topographically and thermallyforced stationary waves: implications on ice-sheetevolution
Open this publication in new window or tab >>Interactions between topographically and thermallyforced stationary waves: implications on ice-sheetevolution
(English)Article in journal (Refereed) Submitted
Abstract [en]

This study examines mutual interactions between stationary waves and ice sheets using a dry atmospheric primitive-equation model coupled to a three-dimensional thermomechanical ice-sheet model. The emphasis is on how nonlinear interactions between thermal and topographical forcing of the stationary waves influence the ice-sheet evolution through the ablation. Simulations are conducted in which a small ice cap, on an idealised Northern Hemisphere continent, evolves to an equilibrium continental-scale ice sheet. In the absence of stationary waves, the equilibrium ice sheet arrives at symmetric shape with a zonal equatorward margin. In isolation, the topographically-induced stationary waves have essentially no impacton the equilibrium features of the ice sheet. The reason is that the response is nonlinearimplying that the temperature anomalies are located far from the equatorward ice margin. When forcing due to thermal cooling is added to the topographical forcing, thermally-induced perturbation winds amplify the topographically-induced stationary-wave response, which serves to increase the equatorward extent of the ice sheet. Hence, the present study suggests that, if the topographically-induced stationary-wave response is nonlinear, it can be substantially amplified by the high albedo of the ice-sheet surface.

National Category
Meteorology and Atmospheric Sciences Climate Research
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-55552 (URN)
Available from: 2011-03-21 Created: 2011-03-21 Last updated: 2011-04-01Bibliographically approved
4. The sensitivity of the Late Saalian (140 ka) and LGM (21 ka) Eurasian ice sheets to sea surface conditions
Open this publication in new window or tab >>The sensitivity of the Late Saalian (140 ka) and LGM (21 ka) Eurasian ice sheets to sea surface conditions
Show others...
2011 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 37, no 3-4, 531-553 p.Article in journal (Refereed) Published
Abstract [en]

This work focuses on the Late Saalian (140 ka) Eurasian ice sheets’ surface mass balance (SMB) sensitivity to changes in sea surface temperatures (SST). An Atmospheric General Circulation Model (AGCM), forced with two preexisting Last Glacial Maximum (LGM, 21 ka) SST reconstructions, is used to compute climate at 140 and 21 ka (reference glaciation). Contrary to the LGM, the ablation almost stopped at 140 ka due to the climatic cooling effect from the large ice sheet topography. Late Saalian SST are simulated using an AGCM coupled with a mixed layer ocean. Compared to the LGM, these 140 ka SST show an inter-hemispheric asymmetry caused by the larger ice-albedo feedback, cooling climate. The resulting Late Saalian ice sheet SMB is smaller due to the extensive simulated sea ice reducing the precipitation. In conclusion, SST are important for the stability and growth of the Late Saalian Eurasian ice sheet.

Keyword
Sea surface temperatures, Late Saalian, Last Glacial Maximum, Eurasian ice sheet, Climate modelling, Quaternary
National Category
Earth and Related Environmental Sciences Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-47308 (URN)10.1007/s00382-010-0870-7 (DOI)000293403500008 ()
Note

authorCount :6

Available from: 2010-11-30 Created: 2010-11-30 Last updated: 2014-05-20Bibliographically approved

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