排序方式: 共有19条查询结果,搜索用时 31 毫秒
1.
Upland gravel-bedded streams in the U.K. have received only scant attention from both hydrologists and sedimentologists, but are worthy of further investigation. The sedimentology of three small streams in Teesdale in the Pennines has been examined in detail. Grain-size characteristics, bedforms, structure, composition and packing characteristics of these deposits are described, and compared where appropriate with published information. It is argued that a fuller appreciation of gravel bed composition and morphology should eventually contribute to an improved understanding of sediment transport and deposition mechanisms, and, hence, to improved accuracy in sediment transport and deposition estimates. 相似文献
2.
3.
The modification of greenhouse gas warming by the direct effect of sulphate aerosols 总被引:1,自引:0,他引:1
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
4.
5.
6.
7.
To explore processes involved in glacial inception at 116 kaBP, the response of an atmospheric general circulation model (AGCM) to changes in lower boundary conditions is investigated. Two 116 kaBP experiments are conducted to examine the importance of sea surface conditions (sea surface temperature and sea ice distribution): one with the present-day sea surface conditions, and the other with 116 kaBP sea surface conditions. These two different sea surface conditions are obtained from simulations using an earth system climate model of intermediate complexity. Perennial snow cover occurred over the Canadian Archipelago under 116 kaBP orbital and CO2 forcing with present-day "warm" sea surface conditions, and further expanded over northeastern Canada when 116 kaBP "cool" sea surface conditions were applied. The net positive accumulation in northeastern Canada, with little in Alaska, is in good agreement with geological records. Two additional 116 kaBP experiments are conducted to examine the combined importance of sea surface conditions and land surface conditions (vegetation): one with the present-day sea surface and modified land surface conditions, and the other with 116 kaBP sea surface and modified land surface conditions. Modifying vegetation, based on cooling during summer induced by 116 kaBP sea surface conditions, leads to much larger areas of perennial snow cover. Only when 116 kaBP sea surface conditions are applied, is a realistic global net snow accumulation rate obtained. Contrary to the earlier ice age hypothesis, our results suggest that the capturing of glacial inception at 116 kaBP requires the use of "cooler" sea surface conditions than those of the present climate. Also, the large impact of vegetation change on climate suggests that the inclusion of the vegetation feedback is important for model validation, at least, in this particular period of Earth history. 相似文献
8.
9.
The Canadian Centre for Climate Modelling and Analysis global coupled model and its climate 总被引:16,自引:5,他引:11
G. M. Flato G. J. Boer W. G. Lee N. A. McFarlane D. Ramsden M. C. Reader A. J. Weaver 《Climate Dynamics》2000,16(6):451-467
A global, three-dimensional climate model, developed by coupling the CCCma second-generation atmospheric general circulation
model (GCM2) to a version of the GFDL modular ocean model (MOM1), forms the basis for extended simulations of past, current
and projected future climate. The spin-up and coupling procedures are described, as is the resulting climate based on a 200 year
model simulation with constant atmospheric composition and external forcing. The simulated climate is systematically compared
to available observations in terms of mean climate quantities and their spatial patterns, temporal variability, and regional
behavior. Such comparison demonstrates a generally successful reproduction of the broad features of mean climate quantities,
albeit with local discrepancies. Variability is generally well-simulated over land, but somewhat underestimated in the tropical
ocean and the extratropical storm-track regions. The modelled climate state shows only small trends, indicating a reasonable
level of balance at the surface, which is achieved in part by the use of heat and freshwater flux adjustments. The control
simulation provides a basis against which to compare simulated climate change due to historical and projected greenhouse gas
and aerosol forcing as described in companion publications.
Received: 24 September 1998 / Accepted: 8 October 1999 相似文献
10.
H.E. Reader 《地理信息系统科学与遥感》2014,51(2):199-211
Estuaries are photochemically dynamic environments with high carbon loads and relatively small areas. The small area poses problems for large-scale satellite-based remote sensing calculations, where the resolution is too coarse to distinguish land from water. Airborne remote sensing instruments have the potential to reveal the dynamics of these areas with fine-scale resolution. In June 2006, hyperspectral remote sensing imagery, using an AISA Eagle instrument, was collected over the tidal Duplin River, Georgia, USA. A dark-water updated version of the SeaUV algorithm was applied to the AISA remote sensing image to determine diffuse attenuation constants in the ultraviolet and calculate surface photochemical production rates of two inorganic products – carbon monoxide (CO) and carbon dioxide (CO2). For an average day in June at the study site, the modeled photoproduction rates for CO2 and CO averaged ~7 × 10?1 nmol C/day/cm3 and ~3.5 × 10?2 nmol C/day/cm3, respectively. 相似文献