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11.
Mauro Dall’Amico Peter A. Stott Adam A. Scaife Lesley J. Gray Karen H. Rosenlof Alexey Yu. Karpechko 《Climate Dynamics》2010,34(2-3):399-417
An improved stratospheric representation has been included in simulations with the Hadley Centre HadGEM1 coupled ocean atmosphere model with natural and anthropogenic forcings for the period 1979–2003. An improved stratospheric ozone dataset is employed that includes natural variations in ozone as well as the usual anthropogenic trends. In addition, in a second set of simulations the quasi biennial oscillation (QBO) of stratospheric equatorial zonal wind is also imposed using a relaxation towards ERA-40 zonal wind values. The resulting impact on tropospheric variability and trends is described. We show that the modelled cooling rate at the tropopause is enhanced by the improved ozone dataset and this improvement is even more marked when the QBO is also included. The same applies to warming trends in the upper tropical troposphere which are slightly reduced. Our stratospheric improvements produce a significant increase of internal variability but no change in the positive trend of annual mean global mean near-surface temperature. Warming rates are increased significantly over a large portion of the Arctic Ocean. The improved stratospheric representation, especially the QBO relaxation, causes a substantial reduction in near-surface temperature and precipitation response to the El Chichón eruption, especially in the tropical region. The winter increase in the phase of the northern annular mode observed in the aftermath of the two major recent volcanic eruptions is partly captured, especially after the El Chichón eruption. The positive trend in the southern annular mode (SAM) is increased and becomes statistically significant which demonstrates that the observed increase in the SAM is largely subject to internal variability in the stratosphere. The possible inclusion in simulations for future assessments of full ozone chemistry and a gravity wave scheme to internally generate a QBO is discussed. 相似文献
12.
Western tropical Pacific sea surface temperatures and Pacific Deep Water temperatures during Marine Isotope Stage 3 have been reconstructed from the δ18O and Mg/Ca of planktonic and benthic foraminifera from Marion Dufresne core MD98-2181. This 36 m marine core was collected at 6.3°N from a water depth of 2114 m. With sediment accumulation rates of up to 80 cm/ky, it provides a decadally resolved history of ocean variability during the Last Glacial period. Surface temperatures and salinities at this site varied in close association with millennial-scale atmospheric temperature swings at high northern latitudes as reflected in the GISP2 ice core. At times of colder atmospheric temperatures over Greenland, the western Pacific was more saline and summer season SSTs were ~2 °C colder. These millennial-scale changes within the tropics are attributed to a southward displacement of the summer season ITCZ in response to steeper meridional temperature gradients within the Pacific. The benthic δ18O record from MD98-2181 documents upper Pacific Deep Water temperature and salinity variability. Benthic δ18O variations of 0.3–0.5‰ during MIS 3 indicate deep waters within the Pacific were varying by ~1–1.5 °C, with the possibility that some of the variability was due to changing salinity and minor glacial–eustatic changes. The observed deep-water variability correlates to changes in Antarctic surface temperatures and thus reflects changes in Southern Ocean temperatures at the site of Pacific Deep Water formation. The combined planktonic and benthic records from MD98-2181 thus provide a northern and southern hemispheric climate record of anti-phased variability during MIS 3 as has been inferred previously from ice core records. Furthermore, the deep sea temperature excursions appear to have led millennial variations in atmospheric CO2 as recorded in the EDML ice core by ~1 kyr. 相似文献
13.
A. M. Swinbank A. C. Edge Ian Smail J. P. Stott M. Bremer Y. Sato C. van Breukelen M. Jarvis I. Waddington L. Clewley J. Bergeron G. Cotter S. Dye J. E. Geach E. Gonzalez-Solares P. Hirst R. J. Ivison S. Rawlings C. Simpson G. P. Smith A. Verma T. Yamada 《Monthly notices of the Royal Astronomical Society》2007,379(4):1343-1351
14.
Nicholas E. Graham Malcolm K. Hughes Caspar M. Ammann Kim M. Cobb Martin P. Hoerling Douglas J. Kennett James P. Kennett Bert Rein Lowell Stott Peter E. Wigand Taiyi Xu 《Climatic change》2007,83(1-2):241-285
Terrestrial and marine late Holocene proxy records from the western and central US suggest that climate between approximately 500 and 1350 a.d. was marked by generally arid conditions with episodes of severe centennial-scale drought, elevated incidence of wild fire, cool sea surface temperatures (SSTs) along the California coast, and dune mobilization in the western plains. This Medieval Climate Anomaly (MCA) was followed by wetter conditions and warming coastal SSTs during the transition into the “Little Ice Age” (LIA). Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific SSTs during the MCA, with warmer than modern temperatures in the western equatorial Pacific. This pattern of mid-latitude and tropical climate conditions is consistent with the hypothesis that the dry MCA in the western US resulted (at least in part) from tropically forced changes in winter NH circulation patterns like those associated with modern La Niña episodes. We examine this hypothesis, and present other analyses showing that the imprint of MCA climate change appears in proxy records from widely distributed regions around the planet, and in many cases is consistent with a cool medieval tropical Pacific. One example, explored with numerical model results, is the suggestion of increased westerlies and warmer winter temperatures over northern Europe during medieval times. An analog technique for the combined use of proxy records and model results, Proxy Surrogate Reconstruction (PSR), is introduced. 相似文献
15.
Attribution of twentieth century temperature change to natural and anthropogenic causes 总被引:6,自引:0,他引:6
P. A. Stott S. F. B. Tett G. S. Jones M. R. Allen W. J. Ingram J. F. B. Mitchell 《Climate Dynamics》2001,17(1):1-21
We analyse possible causes of twentieth century near-surface temperature change. We use an “optimal detection” methodology
to compare seasonal and annual data from the coupled atmosphere-ocean general circulation model HadCM2 with observations averaged
over a range of spatial and temporal scales. The results indicate that the increases in temperature observed in the latter
half of the century have been caused by warming from anthropogenic increases in greenhouse gases offset by cooling from tropospheric
sulfate aerosols rather than natural variability, either internal or externally forced. We also find that greenhouse gases
are likely to have contributed significantly to the warming in the first half of the century. In addition, natural effects
may have contributed to this warming. Assuming one particular reconstruction of total solar irradiance to be correct implies,
when we take the seasonal cycle into account, that solar effects have contributed significantly to the warming observed in
the early part of the century, regardless of any relative error in the amplitudes of the anthropogenic forcings prescribed
in the model. However, this is not the case with an alternative reconstruction of total solar irradiance, based more on the
amplitude than the length of the solar cycle. We also find evidence for volcanic influences on twentieth century near-surface
temperatures. The signature of the eruption of Mount Pinatubo is detected using annual-mean data. We also find evidence for
a volcanic influence on warming in the first half of the century associated with a reduction in mid-century volcanism.
Received: 24 January 2000 / Accepted: 20 April 2000 相似文献
16.
There is increasingly clear evidence that human influence has contributed substantially to the large-scale climatic changes that have occurred over the past few decades. Attention is now turning to the physical implications of the emerging anthropogenic signal. Of particular interest is the question of whether current climate models may be over- or under-estimating the amplitude of the climate system's response to external forcing, including anthropogenic. Evidence of a significant error in a model-simulated response amplitude would indicate the existence of amplifying or damping mechanisms that are inadequately represented in the model. The range of uncertainty in the factor by which we can scale model-simulated changes while remaining consistent with observed change provides an estimate of uncertainty in model-based predictions. With any model that displays a realistic level of internal variability, the problem of estimating this factor is complicated by the fact that it represents a ratio between two incompletely known quantities: both observed and simulated responses are subject to sampling uncertainty, primarily due to internal chaotic variability. Sampling uncertainty in the simulated response can be reduced, but not eliminated, through ensemble simulations. Accurate estimation of these scaling factors requires a modification of the standard "optimal fingerprinting" algorithm for climate change detection, drawing on the conventional "total least squares" approach discussed in the statistical literature. Code for both variants of optimal fingerprinting can be found on . 相似文献
17.
Recent studies of river bank erosion in three catchments in the UK have been characterized by the persistent occurrence of negative erosion‐pin results. The cause of these negative recordings is considered with reference to field data from the Afon Trannon, Nant Tanllwyth and River Arrow, and to a laboratory study of freeze–thaw and desiccation processes. It seems that there is potential for, and in some cases evidence of, a number of different circumstances that generate negative results, but none of these alone is sufficient to explain all incidents. Factors considered include: deposition of sediment during high flows; soil fall from the upper parts of the bank on to lower erosion pins; loosening of the soil surface and expansion/contraction of the soil mass with fluctuations in temperature and moisture content; movement of the erosion‐pin within the bank and human interference. Each has its own implications for the use of erosion pins. Further issues arise when including negative data in subsequent data analysis, and it is demonstrated that attempts to correlate erosion rates with hydro‐meteorological data in order to ascertain causes of erosion will be influenced by the way in which negative data are handled. It is thus suggested that any study of river bank erosion using erosion pins should state whether or not negative data were obtained, and if so, how they were included in data analysis. Failure to include this information could lead to comparison of mean erosion rates that reflect bank processes very differently. The studies presented here offer a clear example of the value of ‘anomalous’ field data: results which do not appear to fit expected patterns can reveal as much about the processes in operation as those that do. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Gareth S. Jones Jonathan M. Gregory Peter A. Stott Simon F. B. Tett Robert B. Thorpe 《Climate Dynamics》2005,25(7-8):725-738
Volcanic ‘super-eruptions’ have been suggested to have significantly influenced the Earth’s climate, perhaps causing glaciations
and impacting on the human population. Climatic changes following a hypothetical ‘super-eruption’ are simulated using a coupled
atmosphere ocean general circulation model, incorporating scaled volcanic stratospheric aerosols. Assumptions are made about
the stratospheric sulphate aerosol loading, size distribution, lifetime, chemical make up and spatial distribution. As this
study is concentrating on the physical climatological impacts over long timescales, microphysics and chemical interactive
processes are not simulated. Near-surface temperatures fall by as much as 10 K globally for a few months and a considerable
deviation from normal temperatures continues for several decades. A warming pattern is evident over northern land masses during
the winter due to increased longwave forcing and a positive AO mode. The overturning rate of the North Atlantic thermohaline
circulation doubles in intensity. Snow and ice increases in extent to a maximum coverage of 35% of the Earth. Despite these
and other impacts longer term climatic changes that could lead to a transition to a glaciation do not occur, for present day
boundary conditions and one possible plausible aerosol loading. 相似文献
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