Seasonal variation of global surface pressure and water vapor   总被引：1，自引：0，他引：1  

TSING-CHANG CHEN  JAU-MING CHEN  SIEGFRIED SCHUBERT  LAWRENCE L. TAKACS 《地球，A辑:动力气象学与海洋学》1997,49(5):613-621

Previous studies have shown that the seasonal variation of global-mean surface pressure ( p _s) results from variation of global-mean water vapor pressure ( p _w). The current study, employing the global data generated by Version 1 of the Goddard Earth Observing System (GEOS-1) Data Assimilation System, shows that seasonal variations of regional p _s and p _w tend to be out of phase (particularly in the subtropics of the two hemispheres) and that the magnitude of the former variation is generally much larger than that of the latter. The seasonal variations of these two quantities are maintained by airmass and water vapor transports by the global divergent circulation, which is driven by the latent heat released by cumulus convection over the water vapor sink, as the "water mass forcing" mechanism predicted. Since p _w and p _s are used often in depicting the climate system, assessments of climate change in terms of the global-mean and regional variations of these two variables should be interpreted with caution.  相似文献   

Thermobarometry and Pressure-Temperature Paths in the Grenville Province of Ontario   总被引：1，自引：0，他引：1  

ANOVITZ  LAWRENCE M.; ESSENE  ERIC J. 《Journal of Petrology》1990,31(1):197-241

To constrain the tectonic and metamorphic history of the GrenvilleProvince of southern Ontario we have quantitatively evaluatedchanges in peak metamorphic pressures and temperatures in theregion. Pressures increase northwest from the Frontenac Axistowards the Grenville Front, and they increase from 4–6kb near Madoc to 10–11 kb south of North Bay. Furtherto the north pressures decrease to 8–9 kb in the GrenvilleFront Tectonic Zone north of the French and Mattawa Rivers.Temperatures form a broad high, reaching 800?C northeast ofParry Sound, and decreasing to 400–500?C in the HastingsLow near Madoc, 600–650?C east towards the Ottawa River,and 650–700?C near Sudbury. This regional P-T distributionis in good agreement with constraints available from the distributionof aluminosilicate polymorphs. Comparison of thermobarometric results with regional tectonicfeatures shows a sharp discontinuity across the Mattawa andFrench Rivers, with a 1–2-kb pressure drop to the north.This implies that the major movement along this zone since theGrenville event was ‘south-side-up’ rather than‘north-side-up’ as suggested by Lumbers (1971).Large P-T discontinuities are not apparent across the domainboundaries mapped by Davidson and co-workers east of Parry Sound,but small discontinuities may exist. Sparse data may indicatethat the Central Metasedimentary Belt equilibrated at 1–2kb lower pressures than the Central Gneiss Terrane. Zoning profiles in garnet-pyroxene pairs have been used to placeconstraints on the metamorphic pressure-temperature-time pathin the Parry Sound, Port Severn, Bancroft, and Mattawa areasof the Grenville Province, Ontario. A nonlinear fitting routinewas used to obtain best-fit core and rim analyses for garnetsand pyroxenes. These results were combined with plagioclasecore/rim analyses to obtain estimates of peak and retrogradeconditions. The resultant retrograde P-Tpath has a slope of7 ? 10 b/?C, and involves pressure changes of 0?6–2?1kb for temperature changes of 60–130?C. Present address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721  相似文献   

Pressure, Temperature and C-O-H Fluid Fugacities across the Amphibolite-Granulite Transition, Northwest Adirondack Mountains, New York     

EDWARDS  R. LAWRENCE; ESSENE  E. J. 《Journal of Petrology》1988,29(1):39-72

Pressures, temperatures, water activities (a_H2O) and fugacitiesof the other C-O-H fluid species have been estimated on a traverseacross the amphibolite-granulite facies boundary in the MajorParagneiss, northwest Adirondacks, N.Y. Two-feldspar pairs givetemperatures ranging from 650?C in the central portion of theunit to 760?C towards the northeast. Biotite-garnet pairs giveerratic temperatures compared to two-feldspar temperatures.This discrepancy appears to be due to retrograde resetting asdetermined from compositional zoning patterns in biotites andgarnets. Some of the discrepancy may also be due to non-idealityof pyrope-almandine mixing or to non-ideality from other components.Pressures ranging from 5?4 kb for the southwestern portion ofthe unit to 8?0 kb in the northeast were determined from anorthite-grossular-sillimanite-quartzbarometry. Minimum pressures of 5?8 kb were also determinedfrom coexisting garnet + rutile. Values of a_H2O of 0?08-0?5estimated from biotite and muscovite dehydration reactions showno correlation with grade. The variability in a_H2O suggeststhat it is locally controlled and that a homogeneous, pervasivefluid was not present during high grade metamorphism. Graphiteequilibria indicate that f_O2 was less than 0?5 log units belowQFM and that if a fluid was present, it was rich in CO₂ andH₂O. P-T-a_H2O values suggest that partial melting did not occurduring metamorphism. Pervasive flooding with CO₂ does not appearto have occurred. The amphibolite-granulite transition at thislocality is characterized by increasing temperature and pressure.  相似文献   

Seasonal and spatial variability of particulate matter of a muddy intertidal flood front   总被引：1，自引：0，他引：1  

FRANZ E. ANDERSON  LAWRENCE M. MAYER† 《Sedimentology》1984,31(3):383-394

The concentration and composition of suspended particulate matter (SPM) were measured weekly for a period of one year in the flood front waters traversing a muddy tidal flat. SPM concentrations were lowest in the winter when portions of the tidal flat were covered with ice, and biological activity was minimal. In contrast, the summer months had the highest SPM concentrations which reflected increased bottom resuspension. The two main sources of SPM were suspended matter carried in from offshore on the flooding tide and resuspended in situ bottom sediments. The offshore source was characterized by low SPM concentrations, coarse textures, and a high content of protein and chlorophyll ‘a’. Samples taken during resuspension events (storms/showers) had high SPM concentrations, finer textures, and were enriched in dead detrital organic material (phaeophytin). At any one time the SPM was primarily an admixture of these two sources. The highest SPM measurements were taken during storm events, with rainfall seeming to play a dominant physical role in aiding resuspension. SPM concentrations, textures, and compositions collected during the storms closely approximated SPM measurements made over newly dug ‘clam flats’.  相似文献   

Coarse-grained sediment gravity flow facies in a large supraglacial lake     

NICHOLAS EYLES  BRYAN M. CLARK  JOHN J. CLAGUE 《Sedimentology》1987,34(2):193-216

Near Williams Lake, in the central interior of British Columbia, the Fraser River exposes long sections of late Pleistocene glaciolacustrine sediments selectively preserved within a bedrock trough. The dominant facies types are thick, normally graded gravels and sands that occupy steeply dipping multistorey channels up to 300 m wide and several tens of metres deep. Channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice. Fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi-continuous ‘surging’ turbidity flows triggered by catastrophic meltwater discharges into the trough or retrogressive failure of ice-cored sediments. Large-scale post-depositional deformation structures, such as synclinal folds, normal faults, sedimentary dyke swarms and dewatering structures, record gravitational foundering of sediment and pore-water expulsion caused by the melt of underlying glacier ice. Melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub-basins within the overlying sediment pile. An idealized model of ‘supraglacial’ lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography.  相似文献   

The late Miocene to Pleistocene ice-rafting history of southeast Greenland     

KRISTEN E. K. ST. JOHN  LAWRENCE A. KRISSEK 《Boreas: An International Journal of Quaternary Research》2002,31(1):28-35

Analysis of a Miocene-Pleistocene ice-rafted debris (IRD) record from the western Irminger Basin provides evidence for the initiation and long-term behavior of the SE portion of the Greenland Ice Sheet. In the late Miocene (~7.3 Ma), IRD supply to Ocean Drilling Program site 918 increased significantly indicating that glaciers large enough to reach sea level were present in SE Greenland long before the onset of widespread Northern Hemisphere glaciation. IRD accumulated at this site throughout the Pliocene and Pleistocene, supporting the hypothesis that SE Greenland was a key nucleation area for the formation of the Greenland Ice Sheet. Since glacial onset, the western Irminger Basin IRD record is characterized by a succession of episodes with high IRD mass accumulation rates (MARs). The site 918 IRD record indicates that greatest iceberg production in SE Greenland occurred during major climatic transitions (e.g. widespread Northern Hemisphere glacial expansion at 2.7 Ma and the mid-Pleistocene climate shift at 0.9 Ma), and that SE Greenland sometimes also led the northern North Atlantic region in glacial response to climatic forcing (e.g. glacial intensification at ~4.8 and, along with NE Greenland, at ~3.5 Ma).  相似文献   

A polygon reduction algorithm for enhancing graphics performance with application to fast rendering of geophysical and ionospheric model data     

BRYAN G. TALBOT  ROBERT E. PETERSON 《International journal of geographical information science》2013,27(8):747-762

Many scientific applications employ computer graphics as a means of interactively visualizing two-dimensional geophysical data sets. This paper presents an algorithm for improving rendering performance by using an image segmentation approach to reduce the number of rendered polygons while maintaining complete display fidelity. Though applied here specifically to the output from a numerical ionosphere model, the algorithm is broadly applicable to many other two-dimensional cellular data sets, geophysical and otherwise. In an ionospheric context, this algorithm demonstrates the ability to reduce the number of rendered polygons by 95 per cent or more with a corresponding reduction in rendering time.  相似文献   

A comparison of scavenging and deposition processes in global models: results from the WCRP Cambridge Workshop of 1995   总被引：2，自引：1，他引：1  

P. J. RASCH  J. FEICHTER  K LAW  N. MAHOWALD  J. PENNER  C. BENKOVITZ  C. GENTHON  C. GIANNAKOPOULOS  P. KASIBHATLA  D. KOCH  H. LEVY  T. MAKI  M. PRATHER  D. L. ROBERTS  G.&#;J. ROELOFS  D. STEVENSON  Z. STOCKWELL  S. TAGUCHI  M. KRITZ  M. CHIPPERFIELD  D. BALDOCCHI  P. McMURRY  L. BARRIE  Y. BALKANSKI  R. CHATFIELD  E. KJELLSTROM  M. LAWRENCE  H. N. LEE  J. LELIEVELD  K. J. NOONE  J. SEINFELD  G. STENCHIKOV  S. SCHWARTZ  C. WALCEK  D. WILLIAMSON 《Tellus. Series B, Chemical and physical meteorology》2000,52(4):1025-1056

We report on results from a World Climate Research Program workshop on representations of scavenging and deposition processes in global transport models of the atmosphere. 15 models were evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against each other, and against observations of these constituents. This paper provides a survey on the simulation differences between models. It identifies circumstances where models are consistent with observations or with each other, and where they differ from observations or with each other. The comparison shows that most models are able to simulate seasonal species concentrations near the surface over continental sites to within a factor of 2 over many regions of the globe. Models tend to agree more closely over source (continental) regions than for remote (polar and oceanic) regions. Model simulations differ most strongly in the upper troposphere for species undergoing wet scavenging processes. There are not a sufficient number of observations to characterize the climatology (long‐term average) of species undergoing wet scavenging in the upper troposphere. This highlights the need for either a different strategy for model evaluation (e.g., comparisons on an event by event basis) or many more observations of a few carefully chosen constituents.  相似文献   

Responsible Geographies: Co-oreating Knowledge in Aotearoa     

ROBERT MCCLEAN  LAWRENCE D. BERG  MICHAEL M. ROCHE 《New Zealand geographer》1997,53(2):9-15

We examine in this paper the potential for (reforming the relations of social scientific research in Aotearoa. Drawing upon our experience of undertaking historical geographical research with and for Ngati-Toa Rangatira, we argue for the need to develop responsible geographies in Aotearoa. We suggest that the metaphors of ‘crossing borders’ and ‘building structures’ might offer one route into the development of such a responsible geography.  相似文献   

SOIL CONSERVATION,POLITICAL ECOLOGY,AND TECHNOLOGICAL CHANGE ON SAINT VINCENT*     

LAWRENCE S. GROSSMAN 《Geographical review》1997,87(3):353-374

ABSTRACT. A political-ecological perspective is used to analyze soil erosion, conservation, and the peasantry on Saint Vincent in the Eastern Caribbean. Peasants farm areas most susceptible to erosion because of the historical development of property relationships. A soil-conservation effort begun in the late 1930s was part of a broader, British Empire-wide program. Local political-economic conditions and the environmental and technical characteristics of the cropping systems influenced the nature of soil conservation on Saint Vincent. Official colonial discourse about erosion reflected a complex mixture of blaming peasants and recognizing their political-economic constraints.  相似文献