 |
| Titel |
A comparison of climate simulations for the last glacial maximum with three different versions of the ECHAM model and implications for summer-green tree refugia |
| VerfasserIn |
K. Arpe, S. A. G. Leroy, U. Mikolajewicz |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1814-9324
|
| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 7, no. 1 ; Nr. 7, no. 1 (2011-02-22), S.91-114 |
| Datensatznummer |
250004399
|
| Publikation (Nr.) |
 copernicus.org/cp-7-91-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
Model simulations of the last glacial maximum (21 ± 2 ka) with the ECHAM3
T42 atmosphere-only, ECHAM5-MPIOM T31 atmosphere-ocean coupled and ECHAM5
T106 atmosphere-only models are compared. The topography, land-sea mask and
glacier distribution for the ECHAM5 simulations were taken from the
Paleoclimate Modelling Intercomparison Project Phase II (PMIP2) data set
while for ECHAM3 they were taken from PMIP1. The ECHAM5-MPIOM T31 model
produced its own sea surface temperatures (SST) while the ECHAM5 T106
simulations were forced at the boundaries by this coupled model SSTs
corrected from their present-day biases and the ECHAM3 T42 model was forced
with prescribed SSTs provided by Climate/Long-Range Investigation, Mapping,
and Prediction project (CLIMAP).
The SSTs in the ECHAM5-MPIOM simulation for the last glacial maximum (LGM)
were much warmer in the northern Atlantic than those suggested by CLIMAP or
Overview of Glacial Atlantic Ocean Mapping (GLAMAP) while the SSTs
were cooler everywhere else. This had a clear effect on the temperatures
over Europe, warmer for winters in western Europe and cooler for eastern
Europe than the simulation with CLIMAP SSTs.
Considerable differences in the general circulation patterns were found in
the different simulations. A ridge over western Europe for the present
climate during winter in the 500 hPa height field remains in both ECHAM5
simulations for the LGM, more so in the T106 version, while the ECHAM3
CLIMAP-SST simulation provided a trough which is consistent with cooler
temperatures over western Europe. The zonal wind between 30° W and
10° E shows a southward shift of the polar and subtropical jets in the
simulations for the LGM, least obvious in the ECHAM5 T31 one, and an
extremely strong polar jet for the ECHAM3 CLIMAP-SST run. The latter can
probably be assigned to the much stronger north-south gradient in the CLIMAP
SSTs. The southward shift of the polar jet during the LGM is supported by
palaeo-data.
Cyclone tracks in winter represented by high precipitation are characterised
over Europe for the present by a main branch from the British Isles to
Norway and a secondary branch towards the Mediterranean Sea, observed and
simulated. For the LGM the different models show very different solutions:
the ECHAM3 CLIMAP-SST simulation shows just one track going eastward from
the British Isles into central Europe, while the ECHAM5 T106 simulation
still has two branches but during the LGM the main one goes to the
Mediterranean Sea, with enhanced precipitation in the Levant. This agrees
with an observed high stand of the Dead Sea during the LGM. For summer the
ECHAM5 T106 simulation provides much more precipitation for the present over
Europe than the other simulations, thus agreeing with estimates by the
Global Precipitation Climatology Project (GPCP). Also during the LGM this
model makes Europe less arid than the other simulations.
In many respects the ECHAM5 T106 simulation for the present is more
realistic than the ECHAM5 T31 coupled simulation and the older ECHAM3 T42
simulation, when comparing them with the European Centre for Medium-Range
Weather Forecasts (ECMWF) reanalysis or the GPCP precipitation data. For
validating the model data for the LGM, pollen, wood and charcoal analyses
were compared with possible summer-green tree growth from model estimates
using summer precipitation, minimum winter temperatures and growing degree
days (above 5 °C). The ECHAM5 T106 simulation suggests for more sites
with findings of palaeo-data, likely tree growth during the LGM than the
other simulations, especially over western Europe. The clear message
especially from the ECHAM5 T106 simulation is that warm-loving summer-green
trees could have survived mainly in Spain but also in Greece in agreement
with findings of pollen or charcoal. Southern Italy is also suggested but
this could not be validated because of absence of palaeo-data.
Previous climate simulations of the LGM have suggested less cold and more
humid climate than that reconstructed from pollen findings. Our model
results do agree more or less with those of other models but we do not find
a contradiction with palaeo-data because we use the pollen data directly
without an intermediate reconstruction of temperatures and precipitation
from the pollen spectra. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|