Evaluating the influence of different vegetation biomes on the global climate   总被引：4，自引：2，他引：4  

P. K. Snyder  C. Delire  J. A. Foley 《Climate Dynamics》2004,23(3-4):279-302

The participation of different vegetation types within the physical climate system is investigated using a coupled atmosphere-biosphere model, CCM3-IBIS. We analyze the effects that six different vegetation biomes (tropical, boreal, and temperate forests, savanna, grassland and steppe, and shrubland/tundra) have on the climate through their role in modulating the biophysical exchanges of energy, water, and momentum between the land-surface and the atmosphere. Using CCM3-IBIS we completely remove the vegetation cover of a particular biome and compare it to a control simulation where the biome is present, thereby isolating the climatic effects of each biome. Results from the tropical and boreal forest removal simulations are in agreement with previous studies while the other simulations provide new evidence as to their contribution in forcing the climate. Removal of the temperate forest vegetation exhibits behavior characteristic of both the tropical and boreal simulations with cooling during winter and spring due to an increase in the surface albedo and warming during the summer caused by a reduction in latent cooling. Removal of the savanna vegetation exhibits behavior much like the tropical forest simulation while removal of the grassland and steppe vegetation has the largest effect over the central United States with warming and drying of the atmosphere in summer. The largest climatic effect of shrubland and tundra vegetation removal occurs in DJF in Australia and central Siberia and is due to reduced latent cooling and enhanced cold air advection, respectively. Our results show that removal of the boreal forest yields the largest temperature signal globally when either including or excluding the areas of forest removal. Globally, precipitation is most affected by removal of the savanna vegetation when including the areas of vegetation removal, while removal of the tropical forest most influences the global precipitation excluding the areas of vegetation removal.  相似文献   

Decadal variability of rainfall in the Sahel: results from the coupled GENESIS-IBIS atmosphere-biosphere model     

G. Wang  E. A. B. Eltahir  J. A. Foley  D. Pollard  S. Levis 《Climate Dynamics》2004,22(6-7):625-637

In this study we investigate the impact of large-scale oceanic forcing and local vegetation feedback on the variability of the Sahel rainfall using a global biosphere-atmosphere model, the coupled GENESIS-IBIS model, running at two different resolutions. The observed global sea surface temperature in the twentieth century is used as the primary model forcing. Using this coupled global model, we experiment on treating vegetation as a static boundary condition and as a dynamic component of the Earth climate system. When vegetation is dynamic, the R30-resolution model realistically reproduces the multi-decadal scale fluctuation of rainfall in the Sahel region; keeping vegetation static in the same model results in a rainfall regime characterized by fluctuations at much shorter time scales, indicating that vegetation dynamics act as a mechanism for persistence of the regional climate. Even when vegetation dynamics is included, the R15 model fails to capture the main characteristics of the long-term rainfall variability due to the exaggerated atmospheric internal variability in the coarse resolution model. Regardless how vegetation is treated and what model resolution is used, conditions in the last three decades of the twentieth century are always drier than normal in the Sahel, suggesting that global oceanic forcing during that period favors the occurrence of a drought. Vegetation dynamics is found to enhance the severity of this drought. However, with both the observed global SST forcing and feedback from dynamic vegetation in the model, the simulated drought is still not as persistent as that observed. This indicates that anthropogenic land cover changes, a mechanism missing in the model, may have contributed to the occurrence of the twentieth century drought in the Sahel.  相似文献   

The oxidation state of lamproitic magmas     

S. F. Foley 《Mineralogy and Petrology》1985,34(3-4):217-238

Summary Olivine leucitites from the Gaussberg volcano, Antarctica are primitive members of the lamproite group of ultrapotassic rocks. They are glass rich, have an Mg number of around 70, and carry spinel lherzolite xenoliths. Liquidus phase fields and compositions were studied experimentally at atmospheric pressure with controlled oxygen fugacities. Chrome-spinels occur as inclusions in olivines in the natural rock, but it was necessary to add Cr₂O₃ to the experiments to stabilize spinels at the liquidus, indicating that some fractionation of spinel has almost certainly occurred.Experimental results show thatfO₂ conditions of crystallization can be characterized by ferric value (100 Fe³⁺/(Fe³⁺+Fe²⁺)) of spinel, ferric iron content of leucite, and Mg-number (100 Mg/(Mg+Fe²⁺)) of olivine. The results demonstrate that the liquidus phases of the Gaussberg rocks crystallized atfO₂ slightly below that of the NNO buffer. Application of the results to other lamproites indicates that they began to crystallize at oxygen fugacities varying from well above NNO (Leucite Hills) to around MW (West Kimberley and the Spanish fortunites). The Gaussberg olivine leucitite contains leucite cores poor in ferric iron with rims richer in ferric iron, indicating oxidation during emplacement. The ferric value of spinel is very sensitive to changes in oxygen fugacity and recognizing that some lamproitic magmas are known to contain diamonds, it may prove to be useful as a diamond survival indicator. The preservation of diamonds in lamproitic rocks will depend critically onfO₂: diamonds are not likely to be preserved in rocks which reach the surface as liquids atfO₂ near NNO or above.

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Der Oxidationsgrad lamproitischer Magmen

Zusammenfassung Die Olivin-Leuzitite vom Gaussberg Vulkan, Antarktis, gehören zu den primären Gliedern der Lamproit-Gruppe der ultra-kalireichen Gesteine. Sie sind reich an Glas, weisen Mg-Werte um 70 auf, und führen Spinell-Lherzolith Xenolithe. Die Liquidus-Phasengleichgewichte bei Atmosphärendruck unter kontrollierten Sauerstoff-Partialdruckbedingungen wurden untersucht. Um Chromit als Liquidusphase zu stabilisieren, war es erforderlich, Cr₂O₃ zu den experimentellen Zusammensetzungen hinzuzufügen, obwohl Chromspinell als Einschluß in Olivin in den Ausgangsgesteinen auftritt; dies deutet eine Spinell-Franktionierung an.Die Resultate zeigten, daß diefO₂-Bedingungen bei der Kristallisation durch das Fe³⁺-Verhältnis (100 Fe³⁺/(Fe³⁺+Fe²⁺)) im Spinell, durch den Fe³⁺-Gehalt im Leuzit, und durch den Mg-Wert (100 mg/(Mg+Fe²⁺)) im Olivin charakterisiert sind. Die Liquidusphasen der Gaussberg Gesteine kristallisierten beifO₂-Bedingungen etwas unterhalb NNO. Die Anwendung der Resultate auf andere Lamproite zeigt, daß diese unter Sauerstoff-Partialdruckbedingungen kristallisierten, die von oberhalb NNO (Leucite Hills) bis etwa MW (West Kimberley und die Spanish Fortunites) variierten. Der Gaussberg Olivin-Leuzitit enthält Leuzitkristalle mit deutlicher Zonierung; die Kernbereiche sind arm an dreiwertigem Eisen, während die Randzonen deutlich an Fe³⁺ angereichert sind. Dies weist auf eine Oxidation des Magmas während der Platznahme hin. Das Fe³⁺-Verhältnis der Spinelle ist sehr empfindlich gegenüber Änderungen des Sauerstoff-Partialdruckes; da einige lamproitische Magmen Diamanten führen, könnte sich dieses als ein sinnvoller Indikator für eine mögliche Diamantführung erweisen. Die Überlebensfähigkeit von Diamanten in lamproitischen Gesteinen wird sehr stark abhängig sein vonfO₂: Magmen, die die Oberfläche unterfO₂-Bedingungen entsprechend NNO oder darüber erreichten, werden keine Diamanten mehr erhalten.

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With 7 Figures  相似文献   

4DVAR data assimilation in the Intra-Americas Sea with the Regional Ocean Modeling System (ROMS)   总被引：2，自引：0，他引：2  

B.S. Powell  H.G. Arango  A.M. Moore  E. Di Lorenzo  R.F. Milliff  D. Foley   《Ocean Modelling》2008,23(3-4):130-145

We present the background, development, and preparation of a state-of-the-art 4D variational (4DVAR) data assimilation system in the Regional Ocean Modeling System (ROMS) with an application in the Intra-Americas Sea (IAS). This initial application with a coarse model shows the efficacy of the 4DVAR methodology for use within complex ocean environments, and serves as preparation for deploying an operational, real-time assimilation system onboard the Royal Caribbean Cruise Lines ship Explorer of the Seas. Assimilating satellite sea surface height and temperature observations with in situ data from the ship in 14 day cycles over 2 years from January 2005 through March 2007, reduces the observation-model misfit by over 75%. Using measures of the Loop Current dynamics, we show that the assimilated solution is consistent with observed statistics.  相似文献   

Cs–Rb–Ba systematics in phengite and amphibole: an assessment of fluid mobility at 2.0 GPa in eclogites from Trescolmen, Central Alps   总被引：3，自引：0，他引：3  

T. Zack  T. Rivers  S. Foley 《Contributions to Mineralogy and Petrology》2001,140(6):651-669

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Oscillations in the Umbral Atmosphere     

N. Brynildsen  P. Maltby  C.R. Foley  T. Fredvik  O. Kjeldseth-Moe 《Solar physics》2004,221(2):237-260

The results of simultaneous observations of oscillations in the chromosphere, transition region, and corona above nine sunspots are presented. The data are obtained through coordinated observing with the Solar and Heliospheric Observatory — SOHO and the Transition Region And Coronal Explorer — TRACE. Oscillations are detected above each umbra. The power spectra show one dominant frequency corresponding to a period close to 3 min. We show that the oscillations in the sunspot transition region can be modeled by upwardly propagating acoustic waves. In the corona the oscillations are limited to small regions that often coincide with the endpoints of sunspot coronal loops. Spectral observations show that oscillations in the corona contribute to the observed oscillations in the TRACE 171 Å channel observations. We show that a recent suggestion regarding a connection between sunspot plumes and 3-min oscillations conflicts with the observations.  相似文献   

Fully coupled climate/dynamical vegetation model simulations over Northern Africa during the mid-Holocene   总被引：6，自引：1，他引：5  

R. Doherty  J. Kutzbach  J. Foley  D. Pollard 《Climate Dynamics》2000,16(8):561-573

 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   

How Accurately Can We Determine the Coronal Heating Mechanism in the Large-Scale Solar Corona?     

Mackay  D.H.  Galsgaard  K.  Priest  E.R.  Foley  C.R. 《Solar physics》2000,193(1-2):93-116

In recent papers by Priest et al., the nature of the coronal heating mechanism in the large-scale solar corona was considered. The authors compared observations of the temperature profile along large coronal loops with simple theoretical models and found that uniform heating along the loop gave the best fit to the observed data. This then led them to speculate that turbulent reconnection is a likely method to heat the large-scale solar corona. Here we reconsider their data and their suggestion about the nature of the coronal heating mechanism. Two distinct models are compared with the observations of temperature profiles. This is done to determine the most likely form of heating under different theoretical constraints. From this, more accurate judgments on the nature of the coronal heating mechanism are made. It is found that, due to the size of the error estimates in the observed temperatures, it is extremely difficult to distinguish between some of the different heat forms. In the initial comparison the limited range of observed temperatures (T>1.5 MK) in the data sets suggests that heat deposited in the upper portions of the loop, fits the data more accurately than heat deposited in the lower portions. However if a fuller model temperature range (T<1.0 MK) is used results in contridiction to this are found. In light of this several improvements are required from the observations in order to produce theoretically meaningful results. This gives serious bounds on the accuracy of the observations of the large-scale solar corona in future satellite missions such a Solar-B or Stereo.  相似文献   

Trace element compositions of minerals in garnet and spinel peridotite xenoliths from the Vitim volcanic field, Transbaikalia, eastern Siberia   总被引：12，自引：0，他引：12  

Sandra M. Glaser  Stephen F. Foley  Detlef Gü  nther 《Lithos》1999,48(1-4):263-285

Peridotite xenoliths from the Bereya alkali picrite tuff in the Vitim volcanic province of Transbaikalia consist of garnet lherzolite, garnet–spinel lherzolite and spinel lherzolite varieties. The volcanism is related to the Cenozoic Baikal Rift. All peridotites come from pressures of 20–23 kbar close to the garnet to spinel peridotite transition depth, and the presence of garnet can be attributed to cooling of spinel peridotites, probably during formation of the lithosphere. The peridotites show petrographic and mineral chemical evidence for infiltration by an alkaline silicate melt shortly before their transport to the Earth's surface. The melt infiltration event is indicated petrographically by clinopyroxenes which mimic melt morphologies, and post-dates outer kelyphitic rims on garnets which are attributed to an isochemical heating event within the mantle before transport to the Earth's surface. Single-mineral thermometry gives reasonable temperature estimates of 1050±50°C, whereas two-mineral methods involving clinopyroxene are falsified by secondary components in clinopyroxene introduced during the melt infiltration event. Excimer Laser–ICP-MS analysis has been performed for an extensive palette of both incompatible and compatible trace elements, and manifests the most thorough dataset available for this rock type. Orthopyroxene and garnet show only partial equilibration of trace elements with the infiltrating melt, whereas clinopyroxene and amphibole are close to equilibration with the melt and with each other. The incompatible element composition of the infiltrating melt calculated from the clinopyroxene and amphibole analyses via experimental mineral/melt partition coefficients is similar to the host alkali picrite, and probably represents a low melt fraction from a similar source during rift propagation. The chemistry and chronology of the events recorded in the xenoliths delineates the series of events expected during the influence of an expanding rift region in the upper mantle, namely the progressive erosion of the lithosphere and the episodic upward and outward propagation of melts, resulting in the evolution of the Vitim volcanic field.  相似文献