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| Titel |
Weather and extremes in the last Millennium - a challenge for climate modelling |
| VerfasserIn |
Christoph C. Raible, Sandro R. Blumer, Juan J. Gomez-Navarro, Flavio Lehner |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102196
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| Publikation (Nr.) |
 EGU/EGU2015-1796.pdf |
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| Zusammenfassung |
| Changes in the climate mean state are expected to influence society, but the socio-economic
sensitivity to extreme events might be even more severe. Whether or not the current
frequency and severity of extreme events is a unique characteristic of anthropogenic-driven
climate change can be assessed by putting the observed changes in a long-term
perspective. In doing so, early instrumental series and proxy archives are a rich source to
investigate also extreme events, in particular during the last millennium, yet they suffer
from spatial and temporal scarcity. Therefore, simulations with coupled general
circulation models (GCMs) could fill such gaps and help in deepening our process
understanding.
In this study, an overview of past and current efforts as well as challenges in modelling paleo
weather and extreme events is presented. Using simulations of the last millennium we
investigate extreme midlatitude cyclone characteristics, precipitation, and their connection to
large-scale atmospheric patterns in the North Atlantic European region. In cold climate states
such as the Maunder Minimum, the North Atlantic Oscillation (NAO) is found
to be predominantly in its negative phase. In this sense, simulations of different
models agree with proxy findings for this period. However, some proxy data available
for this period suggests an increase in storminess during this period, which could
be interpreted as a positive phase of the NAO - a superficial contradiction. The
simulated cyclones are partly reduced over Europe, which is consistent with the
aforementioned negative phase of the NAO. However, as the meridional temperature
gradient is increased during this period – which constitutes a source of low-level
baroclincity – they also intensify. This example illustrates how model simulations
could be used to improve our proxy interpretation and to gain additional process
understanding.
Nevertheless, there are also limitations associated with climate modeling efforts to simulate
the last millennium. In particular, these models still struggle to properly simulate atmospheric
blocking events, an important dynamical feature for dry conditions during summer times.
Finally, new and promising ways in improving past climate modelling are briefly introduced.
In particular, the use of dynamical downscaling is a powerful tool to bridge the gap between
the coarsely resolved GCMs and characteristics of the regional climate, which is
potentially recorded in proxy archives. In particular, the representation of extreme events
could be improved by dynamical downscaling as processes are better resolved than
GCMs. |
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