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1.
 The influence of different vegetation distributions on the atmospheric circulation during the Last Glacial Maximum (LGM, 21 000 years before present) is investigated. The atmospheric general circulation model of the Bureau of Meteorology Research Center was run using a modern vegetation and in a second experiment with a vegetation reconstruction for the LGM. It is found that a change from conifer to desert and tundra causes an additional LGM cooling of 1–2 °C in Western Europe, up to −4 °C in North America and −6 °C in Siberia. An expansion of dryland vegetation causes an additional annual cooling of 1–2 °C for Australia and northern Africa. On the other hand, an increase of temperature (2 °C) is found in Alaska due to changes in circulation. In the equatorial region the LGM vegetation leads to an increased modelled temperature of 0.5–1.5 °C and decreased precipitation (30%) over land due to a reduction of the tropical rainforest, mainly in Indonesia, where the reduction of precipitation over land is associated with an increase of precipitation of 30% over the western Pacific. Received: 15 December 1999 / Accepted: 10 January 2001  相似文献   

2.
 The LMD AGCM was iteratively coupled to the global BIOME1 model in order to explore the role of vegetation-climate interactions in response to mid-Holocene (6000 y BP) orbital forcing. The sea-surface temperature and sea-ice distribution used were present-day and CO2 concentration was pre-industrial. The land surface was initially prescribed with present-day vegetation. Initial climate “anomalies” (differences between AGCM results for 6000 y BP and control) were used to drive BIOME1; the simulated vegetation was provided to a further AGCM run, and so on. Results after five iterations were compared to the initial results in order to identify vegetation feedbacks. These were centred on regions showing strong initial responses. The orbitally induced high-latitude summer warming, and the intensification and extension of Northern Hemisphere tropical monsoons, were both amplified by vegetation feedbacks. Vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons, but in West Africa the summer precipitation increase more than doubled in response to changes in vegetation. In the last iteration, global tundra area was reduced by 25% and the southern limit of the Sahara desert was shifted 2.5 °N north (to 18 °N) relative to today. These results were compared with 6000 y BP observational data recording forest-tundra boundary changes in northern Eurasia and savana-desert boundary changes in northern Africa. Although the inclusion of vegetation feedbacks improved the qualitative agreement between the model results and the data, the simulated changes were still insufficient, perhaps due to the lack of ocean-surface feedbacks. Received: 5 December 1996 / Accepted: 16 June 1997  相似文献   

3.
The influence of surface roughness of deserts on the July circulation   总被引：2，自引：0，他引：2  
The influence of low surface roughness of deserts on the July circulation is examined by employing numerical simulations with a GLAS GCM. Two identical sets of simulations were made with the model starting from the initial state of the atmosphere based on the NMC analysis of observations for June 15, at OOZ for the years 1979 and 1980. The first set, called the Control, had land surface roughness set to 45 cm, everywhere. The second set called the Experiment, had surface roughness set to 0.02 cm for deserts, but 45 cm everywhere else on land. All other prescribed boundary conditions were the same in both runs.A comparative analysis of these simulations showed that the rainfall in the Sahara desert was reduced significantly in both Experiments as compared to the corresponding Controls; the ITCZ (inter-tropical convergence zone) moved southward, to about 14° N, which is close to its observed location at about 10° N. This was primarily caused by the relative moisture divergence from the smoother Sahara. In other deserts, which anyway had little rainfall in the July simulation of the Control run, there was virtually no change. The differences in regional heat and moisture budgets, particularly for the Sahara desert, are significant as compared to the sample standard deviation for a set of three July simulations (i.e., Control runs for three different initial conditions). In a third simulation, in which the surface roughness was changed over all land, similar results were obtained in the Sahara desert region.The study reveals the influence of low surface-roughness of deserts on the July rainfall. For the Sahara desert, this influence is comparable to that of an increase in surface albedo. In nature, formation of deserts leads to reduction of surface roughness as the vegetation perishes and soil erosion ensues. It is inferred that the smoothness of land then causes reduction in rainfall and further promotes desertification.Sigma Data Services through contract # NASA 25900.  相似文献   

4.
Modeling bio-geophysical feedback in the African and Indian monsoon region   总被引：4，自引：1，他引：4  
 An asynchronously coupled global atmosphere-biome model is used to assess the dynamics of deserts and drought in the Sahel, Saudi-Arabia and the Indian subcontinent. Under present-day conditions of solar irradiation and sea-surface temperatures, the model finds two solutions: the first solution yields the present-day distribution of vegetation and deserts and the second shows a northward spread of savanna and xerophytic shrub of some 600 km, particularly in the southwest Sahara. Comparison of atmospheric states associated with these solutions corroborates Charney’s theory of a self-induction of deserts through albedo enhancement in the Sahel. Over the Indian subcontinent, changes in vegetation are mainly caused by a positive feedback between increased soil moisture and stronger summer monsoon. Received: 18 April 1995/Accepted: 17 September 1996  相似文献   

5.
 The mid-Holocene `green' Sahara represents the largest anomaly of the atmosphere-biosphere system during the last 12 000 years. Although this anomaly is attributed to precessional forcing leading to a strong enhancement of the African monsoon, no climate model so far has been able to simulate the full extent of vegetation in the Sahara region 6000 years ago. Here two atmospheric general circulation models (LMD 5.3 and ECHAM 3) are asynchronously coupled to an equilibrium biogeography model to give steady-state simulations of climate and vegetation 6000 years ago, including biogeophysical feedback. The two model results are surprisingly different, and neither is fully realistic. ECHAM shows a large northward extension of vegetation in the western part of the Sahara only. LMD shows a much smaller and more zonal vegetation shift. These results are unaffected by the choice of `green' or modern initial conditions. The inability of LMD to sustain a `green' Sahara 6000 years ago is linked to the simulated strength of the tropical summer circulation. During the northern summer monsoon season, the meridional gradient of sea-level pressure and subsidence over the western part of northern Africa are both much weaker in ECHAM than in LMD in the present as well as the mid-Holocene. These features allow the surface moist air flux to penetrate further into northern Africa in ECHAM than in LMD. This comparison illustrates the importance of correct simulation of atmospheric circulation features for the sensitivity of climate models to changes in radiative forcing, particularly for regional climates where atmospheric changes are amplified by biosphere-atmosphere feedbacks. Received: 20 April 1999 / Accepted: 20 January 2000  相似文献   

6.
Reader  M. C.  Boer  G. J. 《Climate Dynamics》1998,14(7-8):593-607
 The Canadian Centre for Climate Modelling and Analysis (CCCma) second generation climate model (GCMII) consists of an atmospheric GCM coupled to mixed layer ocean. It is used to investigate the climate response to a doubling of the CO2 concentration together with the direct effect of scattering by sulphate aerosols. As expected, the aerosols offset some of the greenhouse gas (GHG) warming; the global annual mean screen temperature change due to doubled CO2 is 3.4 °C in this model and this is reduced to 2.7 °C when an estimate of the direct effect of anthropogenic sulphate aerosols is included. The pattern of climate response to the comparatively localized aerosol forcing is not itself localized, and it bears a striking resemblance to the response pattern that arises from the globally distributed change in GHG forcing. This “non-local” response to “localized” forcing indicates that the pattern of climate response is determined, to first order, by the overall magnitude of the change in forcing rather than its detailed nature or structure. Feedback processes operating in the system apparently determine this pattern by locally amplifying and suppressing the response to the magnitude of the change in forcing. The influence of the location of the change in forcing is relatively small. These “non-local” and “local” effects of aerosol forcing are characterized and displayed and some of their consequences discussed. Effects on the moisture budget and on the energetics of the global climate are also examined. Received: 10 June 1997 / Accepted: 8 January 1998  相似文献   

7.
It has long been recognized that albedo related vegetation feedbacks amplify climate variability in North Africa. Recent studies have revealed that areas of very high albedo associated with certain desert soil types contribute to the current dry climate of the region. We construct three scenarios of North African albedo, one based on satellite measurements, one where the highest albedo resembles that of soils in the desert transition zones, and one based on a vegetation map for the “green Sahara” state of the middle Holocene, ca. 6,000 years ago. Using a series of climate model simulations, we find that the additional amplitude of albedo change from the middle Holocene to the present caused by the very bright desert soils enhances the magnitude of the June-to-August precipitation change in the region of the present Sahara from 0.6 to 1.0 mm/day on average. We also find that albedo change has a larger effect on regional precipitation than changes in either the Earth’s orbit or sea surface temperatures between 6,000 years ago and today. Simulated precipitation agrees rather well with present observations and mid Holocene reconstructions. Our results suggest that there may exist an important climate feedback from soil formation processes that has so far not been recognized.  相似文献   

8.
Summary  The surface air temperature time series of both hemispheres and the North Atlantic European area as well as the Southern Oscillation (SO) index time series were analysed using a wavelet transform technique. The values of the so-called singularity exponents of these series were estimated and compared with such estimations for some surrogate time series artificially created from the observed temperature series. It was concluded that the climate dynamics on interannual and interdecadal scales may be considered as a kind of classical Brownian motion although its consideration as a flicker-noise is also possible. The extracted temperature variations were shown to be closely coupled with the SO process. The wavelet-transformed SO series reveals itself as a whole self-similar “tree” the main branches of which are the appearances of the strongest El-Ninos of 1898 – 1899, 1941 – 1942, and 1982 – 1983. Similar “trees” can be seen in the wavelet-transformed temperature series. Thus, the extracted temperature variations were shown to be closely coupled with the SO process, and a decomposition of the current global climate dynamics into three climatic epochs (of about 40-year long) seems to be appropriate. Received May 4, 1998 Revised April 25, 1999  相似文献   

9.
《Climate Dynamics》2008,30(7-8):887-907
Fire activity has varied globally and continuously since the last glacial maximum (LGM) in response to long-term changes in global climate and shorter-term regional changes in climate, vegetation, and human land use. We have synthesized sedimentary charcoal records of biomass burning since the LGM and present global maps showing changes in fire activity for time slices during the past 21,000 years (as differences in charcoal accumulation values compared to pre-industrial). There is strong broad-scale coherence in fire activity after the LGM, but spatial heterogeneity in the signals increases thereafter. In North America, Europe and southern South America, charcoal records indicate less-than-present fire activity during the deglacial period, from 21,000 to ∼11,000 cal yr BP. In contrast, the tropical latitudes of South America and Africa show greater-than-present fire activity from ∼19,000 to ∼17,000 cal yr BP and most sites from Indochina and Australia show greater-than-present fire activity from 16,000 to ∼13,000 cal yr BP. Many sites indicate greater-than-present or near-present activity during the Holocene with the exception of eastern North America and eastern Asia from 8,000 to ∼3,000 cal yr BP, Indonesia and Australia from 11,000 to 4,000 cal yr BP, and southern South America from 6,000 to 3,000 cal yr BP where fire activity was less than present. Regional coherence in the patterns of change in fire activity was evident throughout the post-glacial period. These complex patterns can largely be explained in terms of large-scale climate controls modulated by local changes in vegetation and fuel load. The readers are requested to refer to the section “List of contributors” for the complete list of author affiliation details.  相似文献   

10.
 An improved concept of the best analogues method was used to reconstruct the Last Glacial Maximum (LGM) climate from a set of botanical records from the former Soviet Union and Mongolia. Terrestrial pollen and macrofossil taxa were grouped into broad classes – plant functional types (PFTs), defined by the ecological and climatic parameters used in the BIOME1 model. PFT scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from Eurasia and North America. In contrast to individual taxa, which exhibit great variability and may not be present in the palaeoassemblages, even in suitable climates, PFTs are more characteristic of the vegetation types. The modified method thus allows climate reconstruction at time intervals with partial direct analogues of modern vegetation (e.g. the LGM). At 18 kBP, mean temperatures were 20–29 °C colder than today in winter and 5–11 °C colder in summer in European Russia and Ukraine. Sites from western Georgia show negative, but moderate temperature anomalies compared to today: 8–11 °C in January and 5–7 °C in July. LGM winters were 7–15 °C colder and summers were 1–7 °C colder in Siberia and Mongolia. Annual precipitation sums were 50–750 mm lower than today across northern Eurasia, suggesting a weakening of the Atlantic and Pacific influences. Reconstructed drought index shows much drier LGM conditions in northern and mid-latitude Russia, but similar to or slightly wetter than today around the Black Sea and in Mongolia, suggesting compensation of precipitation losses by lower-than-present evaporation. Received: 11 May 1998 / Accepted: 25 September 1998  相似文献   

11.
 The climate and vegetation patterns of the middle Holocene (6000 years ago; 6 ka) over Northern Africa are simulated using a fully-synchronous climate and dynamical vegetation model. The coupled model predicts a northward shift in tropical rainforest and tropical deciduous forest vegetation by about 5 degrees of latitude, and an increase in grassland at the present-day simulated Saharan boundaries. The northward expansion of vegetation over North Africa at 6 ka is initiated by an orbitally-induced amplification of the summer monsoon, and enhanced by feedback effects induced by the vegetation. These combined processes lead to a major reduction in Saharan desert area at 6 ka relative to present-day of about 50%. However, as shown in previous asynchronous modelling studies, the coupled climate/vegetation model does not fully reproduce the vegetation patterns inferred from palaeoenvironmental records, which suggest that steppe vegetation may have existed across most of Northern Africa. Orbital changes produce an intensification of monsoonal precipitation during the peak rainy season (July to September), whilst vegetation feedbacks, in addition to producing further increases in the peak intensity, play an important role in extending the rainy season from May/June through to November. The orbitally induced increases in precipitation are relatively uniform from west to east, in contrast to vegetation feedback-induced increases in precipitation which are concentrated in western North Africa. Annual-average precipitation increases caused by vegetation feedbacks are simulated to be of similar importance to orbital effects in the west, whilst they are relatively unimportant farther to the east. The orbital, vegetation and combined orbital and vegetation-induced changes in climate, from the simulations presented in this study, have been compared with results from previous modelling studies over the appropriate North African domain. Consequently, the important role of vegetation parametrizations in determining the magnitude of vegetation feedbacks has been illustrated. Further modelling studies which include the effects of changes in ocean temperature and changes in soil properties may be needed, along with additional observations, to resolve the discrepancy between model predictions of vegetation and palaeorecords for North Africa. Received: 15 June 1999 / Accepted: 14 December 1999  相似文献   

12.
By using a climate system model of intermediate complexity, we have simulated long-term natural climate changes occurring over the last 9000 years. The paleo-simulations in which the model is driven by orbital forcing only, i.e., by changes in insolation caused by changes in the Earth's orbit, are compared with sensitivity simulations in which various scenarios of increasing atmospheric CO2 concentration are prescribed. Focussing on climate and vegetation change in northern Africa, we recapture the strong greening of the Sahara in the early and mid-Holocene (some 9000–6000 years ago), and we show that some expansion of grasslandinto the Sahara is theoretically possible, if the atmospheric CO2 concentration increases well above pre-industrial values and if vegetation growth is not disturbed. Depending on the rate of CO2 increase, vegetation migration into the Sahara can be rapid, up to 1/10th of the Saharan area per decade, but could not exceed a coverage of 45%. In ourmodel, vegetation expansion into today's Sahara is triggered by an increase in summer precipitation which is amplified by a positive feedback between vegetation and precipitation. This is valid for simulations with orbital forcing and greenhouse-gas forcing. However, we argue that the mid-Holocene climate optimum some 9000 to 6000 years ago with its marked reduction of deserts in northern Africa is not a direct analogue for future greenhouse-gas induced climate change, as previously hypothesized. Not only does the global pattern of climate change differ between the mid-Holocene model experiments and the greenhouse-gas sensitivity experiments, but the relative role of mechanisms which lead to a reduction of the Sahara also changes. Moreover, the amplitude of simulated vegetation cover changes in northern Africa is less than is estimated for mid-Holocene climate.  相似文献   

13.
局地经圈环流和沙漠   总被引：3，自引：0，他引：3  
应用 Xie和 Arkin降水资料和 NECP／NCAR再分析资料，研究了撒哈拉和中国西北沙漠地区的干旱气候。结果表明，尽管该两区域都有在年降水量少于50mm的十分干旱的区域，但其年度特征却非常不同。在撒哈拉沙漠中心的南部地区和中国西北沙漠地区，超过70％的降水出现在6－8月；而在撒哈拉沙漠中心以北地区，降水主要集中在12－2月。这种十分干旱的气候不能用Channey提出的生物圈－辐射效应加以解释。由于6－7月的强下沉中心远在撒哈拉强干中心的北部，其形成也不能用Rodwell和Hoskins提出的季风－沙漠机制予以解释。利用局地经圈环流的概念对两地干旱气候的分析和比较发现，局地经圈环流的下沉在12－2月支配着局地的垂直环流，导致干旱气候形成。这时撒哈拉北部的弱的、相对的多雨的气候是因受中海气候型影响所改。而在6－7月局地该为上升运动，其中尤以中国西北地区为显著。因此撒哈拉南部及中国西北的沙漠地区降水多集中在6－8月。不过与此上升运动相伴的是低空来之中、高纬的强而干的北风，它携带的水汽甚少，不利深对流发展。正是这种局地经圈环流导致了该两处干旱气候的形成。  相似文献   

14.
 A coarse-grid global ocean general circulation model (OGCM) is used to determine the role of sub-grid scale eddy parametrization schemes in the response to idealized changes in the surface heat flux, of the same order as expected under increased atmospheric CO2 concentrations. Two schemes are employed. The first (H) incorporates standard horizontal mixing, whereas the second (G) combines both enhanced isopycnal mixing and eddy-induced transport. Uniform surface heating anomalies of +2 W m-2 and −2 W m-2 are applied for 50 years, and the results are compared with a control experiment in which no anomalous heating is imposed. A passive “heat” tracer is applied uniformly (at a rate of 2 W m-2 for 50 years) in a separate experiment. The sea-surface temperature response to global surface heating is generally larger in G, especially in the northern subtropical gyres, along the southern coast of Australia and off the Antarctic coast. A pronounced interhemispheric asymmetry (primarily arising from an anomalous response south of 35 °S) is evident in both H and G. The surface trapping of passive tracers in the Southern Hemisphere is generally greater in G than it is in H, and is particularly pronounced along the prime meridian (0 °E). Dynamical changes (i.e., changes in horizontal and vertical currents, convection, and preferred mixing and eddy transport pathways) enhance surface warming in the tropics and subtropics in both G and H. They are dominated by an anomalous meridional overturning centred on the equator, which may also operate in greenhouse warming experiments using coupled atmosphere-ocean GCMs. Over the Southern Ocean the passive tracer experiments and associated ventilation rates suggest that surface warming will be greater in G than in H. In fact, the contrast between the dynamical responses evident in G and H in the actual heating experiments leads to a situation in which the reverse is often true. Overall, dynamical changes enhance the interhemispheric assymetry, more so in G than in H. Received: August 1996/Accepted: 20 March 1997  相似文献   

15.
 This work concerns an analysis of inter-basin and inter-layer exchanges in the component ocean part of the coupled ECHAM4/OPYC3 general circulation model, aimed at documenting the simulation of North Atlantic Deep Water (NADW) and related thermohaline circulations in the Indian and Pacific Oceans. The modeled NADW is formed mainly in the Greenland– Iceland–Norwegian Seas through a composite effect of deep convection and downward cross-isopycnal transport. The modeled deep-layer outflow of NADW can reach 16 Sv near 30 °S in the South Atlantic, with the corresponding upper-layer return flow mainly coming from the “cold water path” through Drake Passage. Less than 4 Sv of the Agulhas “leakage” water contributes to the replacement of NADW along the “warm water path”. In the South Atlantic Ocean, the model shows that some intermediate isopycnal layers with potential densities ranging between 27.0 and 27.5 are the major water source that compensate the NADW return flow and enhance the Circumpolar Deep Water (CDW) flowing from the Atlantic into Indian Ocean. The modeled thermohaline circulations in the Indian and Pacific Oceans indicate that the Indian Ocean may play the major role in converting deep water into intermediate water. About 16 Sv of the CDW-originating deep water enters the Indian Ocean northward of 31 °S, of which more than 13 Sv “upwell” mainly near the continental boundaries of Africa, South Asia and Australia through inter-layer exchanges and return to the Antarctic Circumpolar Current (ACC) as intermediate-layer water. As a contrast, only 4 Sv of Pacific intermediate water is connected to “upwelling” flow southward across 31 °S while the magnitude of northward deep flow across 31 °S in the Pacific Ocean is significantly greater than that in the Indian Ocean. The model suggests that a large portion of the deep waters entering the Pacific Ocean (about 14 Sv) “upwells” continually into some upper layers through the thermocline, and becomes the source of the Indonesian throughflow. Uncertainties in these results may be related to the incomplete adjustment of the model’s isopycnal layers and the sensitivity of the Indonesian throughflow to the model’s geography and topography. Received: 12 August 1997/Accepted: 12 March 1998  相似文献   

16.
 The possible future impact of anthropogenic forcing upon the circulation of the Mediterranean, and the exchange through the Strait of Gibraltar is investigated using a Cox-type model of the Mediterranean at 0.25° × 0.25° resolution, forced by “control” and “greenhouse” scenarios provided by the HadCM2 coupled climate model. The current structure of the Mediterranean forced by the “control” climate is compared with observations: certain aspects of the present circulation are reproduced, but others are absent or incorrectly represented. Deficiencies are most probably due to weaknesses in the forcing climatology generated by the climate model, so some caution must be exercised in interpreting the enhanced greenhouse simulation. Comparison of the control and greenhouse scenarios suggests that deep-water production in the Mediterranean may be reduced or cease in the relatively near future. The results also suggest that the Mediterranean outflow, may become warmer and more saline, but less dense, and hence shallower. The volume of the exchange at the Strait of Gibraltar seems to be relatively insensitive to future climate change, however. Our results indicate that a parameterisation of Gibraltar exchange and Mediterranean Outflow Water (MOW) production may be able to provide adequate representation of the changes we observe for the purposes of the current generation of climate models. Received: 10 August 1998 / Accepted: 11 October 1999  相似文献   

17.
 A new simple, coupled climate model is presented and used to investigate the sensitivity of the thermohaline circulation and climate to ocean vertical and horizontal exchange. As formulated, the model highlights the role of thin, ocean surface layers in the communication between the atmosphere and the subsurface ocean. Model vertical exchange is considered to be an analogue to small-scale, diapycnal mixing and convection (when present) in the ocean. Model horizontal exchange is considered to be an analogue to the effects of the wind-driven circulation. For small vertical exchange in the ocean, the model exhibits only one steady-state solution: a relatively cold, mid-high-latitude climate associated with a weak, salinity-driven circulation (“off ” mode). For large vertical and horizontal exchange in the ocean, the model also exhibits only one steady-state solution: a relatively warm, mid-high-latitude climate associated with a strong, thermally-driven circulation (“on” mode). For sufficiently weak horizontal exchange but large enough vertical exchange, both modes are possible stable, steady-state solutions. When model parameters are calibrated to fit tracer distributions of the modern ocean-atmosphere system, only the “on” mode is possible in this standard case. This suggests that the wind-driven circulation in consort with diapycnal mixing suppresses the “off ” mode in the modern ocean-atmosphere system. Since both diapycnal mixing and the wind-driven circulation would be expected to increase in a cold climate with greater meridional temperature gradients and enhanced winds, vertical and horizontal exchange in the ocean are probably associated with strong negative feedbacks which tend to stabilize climate. These results point to the need to resolve ocean wind-driven circulation and to greatly improve the treatment of ocean diapycnal mixing in more complete models of the climate system. Received: 16 November 1999 / Accepted: 19 June 2000  相似文献   

18.
F. Chen 《Climate Dynamics》2005,24(7-8):667-684
The International Satellite Land-Surface Climatology Project (ISLSCP) Initiative-I 1-degree 1987–1988 data were used to drive a land surface model (LSM) to simulate global surface energy budgets. Simulated surface heat fluxes show remarkable spatial variability and seem to capture well their annual and interannual variability. A shift of maximum evaporation across the equator is more closely related to the seasonal shifting of precipitation pattern than to surface radiation changes. The NCEP/NCAR reanalysis did not reflect this shift, presumably due to its dominant rainfall maximum in the Southern Hemisphere. To assess the “reliability” of these fields, both Global Soil Wetness Project (GSWP) and reanalysis were verified against observations, at two sites. Monthly mean ISLSCP forcing conditions agree fairly well with observations, but its precipitation is usually lower during spring and summer. Low summer GSWP evaporation may be due to low precipitation and incorrect specification of vegetation and soil conditions. The reanalysis had larger seasonal variability than GSWP and observations, and overestimated summer heat fluxes because of its large rainfall and surface radiation. Despite uncertainty in ISLSCP data, an LSM with a modest treatment of vegetation was able to capture reasonably well the seasonal variations in surface heat fluxes at global scales. With some caution, these types of simulations can be used as “pseudo-observations” to evaluate climate-model simulations and to investigate global energy budgets. For the next phase of ISLSCP data development, higher resolution data, which can reflect local heterogeneity of vegetation and soil characteristics, include more rain gauge data are highly desirable to improve model simulations.  相似文献   

19.
In order to investigate Last Glacial Maximum and future climate, we “precalibrate” the intermediate complexity model GENIE-1 by applying a rejection sampling approach to deterministic emulations of the model. We develop ~1,000 parameter sets which reproduce the main features of modern climate, but not precise observations. This allows a wide range of large-scale feedback response strengths which generally encompass the range of GCM behaviour. We build a deterministic emulator of climate sensitivity and quantify the contributions of atmospheric (±0.93°C, 1σ) vegetation (±0.32°C), ocean (±0.24°C) and sea–ice (±0.14°C) parameterisations to the total uncertainty. We then perform an LGM-constrained Bayesian calibration, incorporating data-driven priors and formally accounting for structural error. We estimate climate sensitivity as likely (66% confidence) to lie in the range 2.6–4.4°C, with a peak probability at 3.6°C. We estimate LGM cooling likely to lie in the range 5.3–7.5°C, with a peak probability at 6.2°C. In addition to estimates of global temperature change, we apply our ensembles to derive LGM and 2xCO2 probability distributions for land carbon storage, Atlantic overturning and sea–ice coverage. Notably, under 2xCO2 we calculate a probability of 37% that equilibrium terrestrial carbon storage is reduced from modern values, so the land sink has become a net source of atmospheric CO2.  相似文献   

20.
An established three stage sequential leach scheme was applied to a series of selected high volume aerosol samples (n = 35) collected from the Turkish Eastern Mediterranean coastline (Erdemli). Samples were selected according to their air mass back trajectory history to reflect the contrasting mixtures of aerosol material present in the Eastern Mediterranean marine aerosol. Two populations were adopted, those samples which were classed as “anthropogenic” and those which were “Saharan” dominated aerosol populations. Applying the three stage leach it was possible to define the proportion for each of the considered metals (Al, Fe, Cu, Pb, Cd, Zn and Mn) present in the (a) “exchangeable” (b) “carbonate / oxide” and (c) “refractory” phases, representing novel solid state aerosol speciation data for this marine system. Clear trends were established, conforming with data from previous studies with mainly crustal derived metals (Al and Fe) being present in the refractory phases (Al > 88%; Fe > 84%) and those influenced by anthropogenic sources being dominating in the exchangeable phase, although for these metals the variability was comparatively high (12–64%; 19–85%; 40–100% for Zn, Pb and Cd, respectively). For the majority, greater exchangeable fractions were present the lower the crustal source contribution to the aerosol population, whereas the “refractory” fraction exhibited contrasting behaviour. This was illustrated by the novel application of the mixing diagram, presenting each of the three speciation stages against the corresponding percent anthropogenic contribution to each collected sample. Zn, Pb and Cd all illustrated progressive decrease in the percent exchangeable with increasing crustal contribution to the aerosol population. The percent exchangeable was discussed in terms of its use to represent the upper limit of the bioavailable fraction of metal associated with the aerosol, post deposition. The mixing diagram approach enabled the prediction of the residual fractions for Cd, Pb and Zn (41 ± 4%; 62 ± 4% and 82 ± 5%, respectively,) in Saharan end-member material.  相似文献   

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