 |
| Titel |
Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle |
| VerfasserIn |
Marcus Löfverström, Rodrigo Caballero, Johan Nilsson |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110612
|
| Publikation (Nr.) |
 EGU/EGU2015-10628.pdf |
|
|
|
|
|
| Zusammenfassung |
| Much effort has been devoted to understanding the circulation and climate of the Last Glacial
Maximum (LGM) whereas the long build-up phase to the LGM has received much less
attention. We present modelling results of the atmospheric circulation at three stages of the
last glacial cycle, the LGM and two earlier stages with smaller ice sheets as well as the
interglacial. The paleo-simulations are forced by ice sheet reconstructions consistent with
geological evidence and by appropriate insolation and greenhouse gas concentrations. The
results suggest that the large-scale features of the atmospheric winter circulation
remained qualitatively similar to the interglacial for the larger part of the glacial
cycle. The proposed explanation is that the incipient ice sheets were located in areas
where their interaction with the mean flow is limited. In North America the cyclonic
deflection of the mean flow east of the Rockies yielded a low-level wind largely
parallel to the ice sheet topography. Similarly, the influence of the Eurasian ice
sheet is found to be weak as the ice sheet was located north of the strongest mean
flow.
However, the continental-scale Laurentide ice sheet at the LGM induces a stronger planetary
wave response that leads to structural changes in the atmospheric circulation and a
zonalisation of the Atlantic jet. A possible explanation for the zonalisation of the jet axis is
that the amplified orographic wave is reflected nonlinearly in a subtropical critical layer.
Simulations with varying heights of the ice sheet topography give support to this hypothesis
as the wave activity flux shows evidence of reflection when the ice sheet is sufficiently high. |
|
|
|
|
|