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21.
Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints 总被引：2，自引：2，他引：2
V. Masson-Delmotte M. Kageyama P. Braconnot S. Charbit G. Krinner C. Ritz E. Guilyardi J. Jouzel A. Abe-Ouchi M. Crucifix R. M. Gladstone C. D. Hewitt A. Kitoh A. N. LeGrande O. Marti U. Merkel T. Motoi R. Ohgaito B. Otto-Bliesner W. R. Peltier I. Ross P. J. Valdes G. Vettoretti S. L. Weber F. Wolk Y. YU 《Climate Dynamics》2006,26(5):513-529
Climate model simulations available from the PMIP1, PMIP2 and CMIP (IPCC-AR4) intercomparison projects for past and future
climate change simulations are examined in terms of polar temperature changes in comparison to global temperature changes
and with respect to pre-industrial reference simulations. For the mid-Holocene (MH, 6,000 years ago), the models are forced
by changes in the Earth’s orbital parameters. The MH PMIP1 atmosphere-only simulations conducted with sea surface temperatures
fixed to modern conditions show no MH consistent response for the poles, whereas the new PMIP2 coupled atmosphere–ocean climate
models systematically simulate a significant MH warming both for Greenland (but smaller than ice-core based estimates) and
Antarctica (consistent with the range of ice-core based range). In both PMIP1 and PMIP2, the MH annual mean changes in global
temperature are negligible, consistent with the MH orbital forcing. The simulated last glacial maximum (LGM, 21,000 years
ago) to pre-industrial change in global mean temperature ranges between 3 and 7°C in PMIP1 and PMIP2 model runs, similar to
the range of temperature change expected from a quadrupling of atmospheric CO2 concentrations in the CMIP simulations. Both LGM and future climate simulations are associated with a polar amplification
of climate change. The range of glacial polar amplification in Greenland is strongly dependent on the ice sheet elevation
changes prescribed to the climate models. All PMIP2 simulations systematically underestimate the reconstructed glacial–interglacial
Greenland temperature change, while some of the simulations do capture the reconstructed glacial–interglacial Antarctic temperature
change. Uncertainties in the prescribed central ice cap elevation cannot account for the temperature change underestimation
by climate models. The variety of climate model sensitivities enables the exploration of the relative changes in polar temperature
with respect to changes in global temperatures. Simulated changes of polar temperatures are strongly related to changes in
simulated global temperatures for both future and LGM climates, confirming that ice-core-based reconstructions provide quantitative
insights on global climate changes.
An erratum to this article can be found at 相似文献
22.
The conditions of development of mid-latitude depressions (synoptic eddies) in the winter Northern Hemisphere mid-latitudes
at the Last Glacial Maximum (LGM, 21 000 years ago) are very different from the present ones: this period is characterised
by a general cooling of the extra-tropics, with massive ice sheets over the Northern Hemisphere continents and sea-ice extending
very far south over the North Atlantic. The present work uses regression analysis to study the characteristics of the synoptic
eddies in present-day and LGM climate simulations by the Atmospheric General Circulation Model (AGCM) of the UK Universities'
Global Atmospheric Programme (UGAMP). In the LGM experiment, the structure of the Pacific eddies is similar to the present-day
(PD) situation, but they are weaker. On the other hand, the Atlantic eddies show an increased zonal wavelength and a much
shallower structure in the temperature and vertical wind perturbations. To understand the changes of these characteristics
from present-day to LGM, we compare them to those computed for the most unstable modes of the corresponding mean flows, determined
using a dry primitive equation model. A normal-mode stability analysis is carried both on zonally symmetric and asymmetric
flows for each of the Northern Hemisphere storm-tracks. The changes in the most unstable normal modes found by both these
analyses give a good account of changes in the structure of the perturbations as retrieved from the AGCM, suggesting that
changes in the mean state (especially the temperature gradient) is the main driver of these changes. However in the case of
the present-day Atlantic storm-track, the growth rate of these modes is found to be very low compared to the other cases.
A complementary analysis evaluates the importance of non-modal growth, in the form of downstream development of perturbations,
for each of the storm-tracks. This type of growth is found to be especially important in the case of the present-day Atlantic
storm-track.
Received: 29 September 1999 / Accepted: 17 November 1999 相似文献
23.
A ductile shear zone within a metasomatic biotite band in the Ryoke granite, Teshima, SW Japan, has been studied using the scanning X-ray analytical microscope (SXAM). This enabled the quantitative distributions of major elements, such as Si, K, Fe, Al and Ca, to be determined within the shear zone. These element maps were processed to transform them into images showing the distribution of minerals such as quartz, biotite, plagioclase and K-feldspar, which form the major minerals within the biotite band and the granite protolith. Mineral profiles based on these mineral maps compared with the simple shear strain profile reveal that the shear zone is most intense where quartz and biotite have been substituted for the primary mineral assemblage of the granite protolith, suggesting that the stresses imposed on the granite caused the shear strain to localize along the biotite band to produce the observed shear zone. It appears that the rheological behavior changed around 50–60% of quartz modal composition. 相似文献