Fluctuation dissipation in a general circulation model     

Gerald R North  Robert E Bell  James W Hardin 《Climate Dynamics》1993,8(6):259-264

This paper considers the climate response to step function changes in the solar constant in two versions of a general circulation model with simplified geography. The NCAR CCM0 model is applied to an all-land planet with no topography (Terra Blanda). In one version there is moisture in the air (as well as self-generated clouds) as evaporated from an ideal surface at a fixed 80% of saturation. In the other version there is no moisture in the atmosphere. We examine the decay of natural anomalies in the large-scale temperature field in each model and compare the time dependence of the ensemble average with the average temporal behavior of the response to step function changes in the solar constant. The fluctuation-dissipation theorem of statistical mechanics makes specific predictions about the relationship between the two curves. We conduct the experiments for both versions of the model since the sensitivity is quite different for each. The theorem is found to hold reasonably well in each case.  相似文献   

Greenhouse sensitivity experiments with penetrative cumulus convection and tropical cirrus albedo effects     

Warren M Washington  Gerald A Meehl 《Climate Dynamics》1993,8(5):211-223

Results are presented from two versions of a global R15 atmospheric general circulation model (GCM) coupled to a nondynamic, 50-m deep, slab ocean. Both versions include a penetrative convection scheme that has the effect of pumping more moisture higher into the troposphere. One also includes a simple prescribed functional dependence of cloud albedo in areas of high sea-surface temperature (SST) and deep convection. Previous analysis of observations has shown that in regions of high SST and deep convection, the upper-level cloud albedos increase as a result of the greater optical depth associated with increased moisture content. Based on these observations, we prescribe increased middle- and upper-level cloud albedos in regions of SST greater than 303 K where deep convection occurs. This crudely accounts for a type of cloud optical property feedback, but is well short of a computed cloud-optical property scheme. Since great uncertainty accompanies the formulation and tuning of such schemes, the prescribed albedo feedback is an intermediate step to examine basic feedbacks and sensitivities. We compare the two model versions (with earlier results from the same model with convective adjustment) to a model from the Canadian Climate Centre (CCC) having convective adjustment and a computed cloud optical properties feedback scheme and to several other GCMs. The addition of penetrative convection increases tropospheric moisture, cloud amount, and planetary albedo and decreases net solar input at the surface. However, the competing effect of increased downward infrared flux (from increased tropospheric moisture) causes a warmer surface and increased latent heat flux. Adding the prescribed cirrus albedo feedback decreases net solar input at the surface in the tropics, since the cloud albedos increase in regions of high SST and deep convection. Downward infrared radiation (from increased moisture) also increases, but this effect is overpowered by the reduced solar input in the tropics. Therefore, the surface is somewhat cooler in the tropics, latent heat flux decreases, and global average sensitivity to a doubling of CO₂ with regard to temperature and precipitation/evaporation feedback is reduced. Similar processes, evident in the CCC model with convective adjustment and a computed cloud optical properties feedback scheme, occur over a somewhat expanded latitudinal range. The addition of penetrative convection produces global effects, as does the prescribed cirrus albedo feedback, although the strongest local effects of the latter occur in the tropics.Portions of this study are supported by the Office of Health and Environmental Research of the U.S. Department of Energy as part of its Carbon Dioxide Research Program, and by the Electric Power Research Institute as part of its Model Evaluation Consortium for Climate Assessment ProjectThe National Center for Atmospheric Research is sponsored by the National Science Foundation  相似文献   

Conference on international boundaries and boundary conflict resolution,University of Durham 15–17 July 1989     

Gerald Blake Dr. 《GeoJournal》1990,20(4):431-431

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4525282 Method of loading and/or transferring environmentally harmful materials in shallow-water and mudland regions and artificial Islands suitable therefor     

Erich O Bartsch  Gerald Vollstedt 《Marine pollution bulletin》1985,16(12):i-ii

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Contemporary and palaeo channel patterns and the late quaternary stratigraphy of Cooper Creek,Southwest Queensland,Australia     

Brian R. Rust  Gerald C. Nanson 《地球表面变化过程与地形》1986,11(6):581-590

Braided and anastomosing channels make up two major coexistent networks in the mud-dominated fluvial system of Cooper Creek, Southwest Queensland. The floodplain is characterized by a system of mud braids operative when floods inundate the whole alluvial surface. Anastomosing channels are inset deeper into the floodplain, operate at modern flows, and transport a traction load of sand. Shallow stratigraphic data show that an underlying sand sheet is unrelated to surface channel patterns and was formed by a system of meandering streams. According to preliminary dates based on thermoluminescence, the change from a sand- to mud-dominated fluvial regime took place between 50 000 and 200 000 years B.P., and probably reflects increasing aridity.  相似文献   

Book reviews     

John A. Couch  Michael T. Ledbetter  Gerald N. Smith  John D. Boon 《Estuaries and Coasts》1986,9(3):229-231

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Processes controlling precipitation of carbonate cement and dissolution of silica in reef and near-reef settings     

Samuel A. Epstein  Gerald M. Friedman 《Sedimentary Geology》1982,33(3):157-171

Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partially replaces detrital quartz grains. The uptake and release of CO₂ by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation simulating the natural settings show minimum values of CO₂ (1.9 mmoles 1^?1) and HCO₃^? (2.4 meq 1^?1) in association with maximum values of pH (9.8) and O₂ (> 100% oxygen saturation) in waters covering corals and algae prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O₂ (<66% oxygen saturation) occur with maximum values of CO₂ (2.7 mmoles 1^?1) and HCO₃^? (2.7 meq 1^?1). Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 7.5–7.6) or O₂ (80–90% oxygen saturation) measurements. Seawater adjacent to reef biomass, with elevated pH and supersaturated with calcium carbonate, is periodically pumped into the underlying reef and beach sediments due to pressure-buildups between the reef framework or algal zones and open waters. Carbonate precipitation and quartz dissolution follow. As the system equilibrates, pH values progressively decrease.  相似文献   

Proterozoic aeolian quartz arenites from the Hornby Bay Group, Northwest Territories, Canada: Implications for Precambrian aeolian processes     

Gerald M. Ross 《Precambrian Research》1983,20(2-4)

The Hornby Bay Group is a Middle Proterozoic 2.5 km-thick succession of terrestrial siliciclastics overlain by marine siliciclastics and carbonates. A sequence of conglomeratic and arenaceous rocks at the base of the group contains more than 500 m of mature hematitic quartz arenite interpreted to have been deposited by migrating aeolian bedforms. Bedforms and facies patterns of modern aeolian deposits provided a basis for recognizing two sequences of aeolian arenite. Both sequences interfinger with alluvial—wadi fan conglomerates and arenites deposited by braided streams. Depositional processes, facies patterns and paleotopographic position of the arenites are consistent with modern sand sea dynamics.Distal aeolian facies in both sequences are composed of trough crossbed megasets deposited by climbing, sinuous-crested, transverse dunes. Megasets comprise a gradational assemblage of tabular to wedge-planar cosets formed by deflation/reactivation of dune lee slopes and migration of smaller superposed aeolian bedforms (small dunes and wind ripples). Megasets in the proximal facies are thinner, display composite internal stratification and have a tabular-planar geometry which suggests that they were formed by smaller, straight-crested transverse dunes. Most stratification within the crossbeds is inferred to have formed by the downwind climbing of aeolian ripples across the lee slopes of dunes.Remarkably few Precambrian aeolian deposits have been reported previously. This seems anomalous, because most Precambrian fluvial sediments appear to have been deposited by low sinuosity (braided) streams, the emergent parts of which are prime areas for aeolian deflation. Frequent floods and rapid lateral migration of Precambrian humid climate fluvial systems probably restricted aeolianite deposition to arid paleoclimates. Thus the apparent anomaly may reflect non-recognition and/or non-preservation of aeolianites and/or variations in some aspect of sand sea formation and migration unique to the Precambrian. Reconstruction of the Hornby Bay Group aeolianites using recently developed criteria for their recognition suggests that the latter reason did not exert a strong influence.  相似文献   

Textures of sandstones and carbonate rocks in the world's deepest wells (in excess of 30,000 ft or 9.1 km): Anadarko Basin,Oklahoma—Reply     

Gerald M. Friedman 《Sedimentary Geology》1983,35(2):156-157

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Aluminum-26 in meteorites—VII. Ureilites,their unique radiation history     

Laurel L Wilking  Gerald F Herman  Edward Anders 《Geochimica et cosmochimica acta》1973,37(7):1803-1810

Cosmogenic ²⁶A1 activities have been measured by γ-γ coincidence counting in the three ureilites which had not previously been studied. The values in dpm/kg are: Dingo Pup Donga, 38.4 ± 2.4; North Haig, 39.3 ± 4.8; Dyalpur, 55.8 ± 4.8. Five of the six known ureilites thus have lower ²⁶A1 contents, 63 per cent to 77 per cent, than the calculated saturation values, in marked contrast to most other stony meteorites. This cannot be attributed to short cosmic ray exposure ages. Nor do size and depth effects account for the narrow range of ²⁶A1 activities, because a nuclear particle track study indicates that preatmospheric radii were highly variable, from ≥ 40 cm for Goalpara to only a few cm for Dingo Pup Donga. By default, the most likely explanation is that the ureilites had much smaller or much larger orbits than all other stony meteorites.  相似文献