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991.
Climate is simulated for reference and mitigation emissions scenarios from Integrated Assessment Models using the Bern2.5CC
carbon cycle–climate model. Mitigation options encompass all major radiative forcing agents. Temperature change is attributed
to forcings using an impulse–response substitute of Bern2.5CC. The contribution of CO2 to global warming increases over the century in all scenarios. Non-CO2 mitigation measures add to the abatement of global warming. The share of mitigation carried by CO2, however, increases when radiative forcing targets are lowered, and increases after 2000 in all mitigation scenarios. Thus,
non-CO2 mitigation is limited and net CO2 emissions must eventually subside. Mitigation rapidly reduces the sulfate aerosol loading and associated cooling, partly
masking Greenhouse Gas mitigation over the coming decades. A profound effect of mitigation on CO2 concentration, radiative forcing, temperatures and the rate of climate change emerges in the second half of the century. 相似文献
992.
Size segregated sampling of aerosol particles at the coal-fired power station Šoštanj, Slovenia was performed by a newly developed
system. In addition, simultaneous sampling of particles was performed at two locations, Velenje and Veliki vrh, chosen on
the basis of long term monitoring of SO2 in the influential area of power plant. The signature of the power plant (e.g. characteristic size distributions of some
typical trace elements) was identified. For elements, like As, Mo, Cd and Ga, which are typical for coal combustion, the highest
concentrations were observed in the size range between 1 and 4 μm. For Se and sometimes for Ga two modes were identified,
first between 0.1 and 0.5 μm and second between 1 and 4 μm. Ratios between the average concentrations of selected elements
in fine and coarse particles collected at Veliki vrh (the most influenced location) and Velenje (usually not influenced by
the thermo power station) were significantly higher than 1 in the case of Mo and Se for coarse and fine size range, while
for As the ratio was higher than 1 for the coarse fraction. Consequently, Mo, Se and As were found as the most important tracers
for the emissions from the investigated source. On the basis of the ratios between the concentrations of elements measured
in particles at low and high SO2 concentrations at Veliki vrh, Cd was shown to be a typical tracer as well. Our results definitely showed that size segregated
measurements of particles at the source and in the influenced area give more precise information on the influence of source
to the surrounding region. It was found that patterns of size distributions for typical trace elements observed at the source
are found also in the influenced area, i.e. Veliki vrh. 相似文献
993.
Allison L. Steiner Jeremy S. Pal Sara A. Rauscher Jason L. Bell Noah S. Diffenbaugh Aaron Boone Lisa C. Sloan Filippo Giorgi 《Climate Dynamics》2009,33(6):869-892
Coupling of the Community Land Model (CLM3) to the ICTP Regional Climate Model (RegCM3) substantially improves the simulation
of mean climate over West Africa relative to an older version of RegCM3 coupled to the Biosphere Atmosphere Transfer Scheme
(BATS). Two 10-year simulations (1992–2001) show that the seasonal timing and magnitude of mean monsoon precipitation more
closely match observations when the new land surface scheme is implemented. Specifically, RegCM3–CLM3 improves the timing
of the monsoon advance and retreat across the Guinean Coast, and reduces a positive precipitation bias in the Sahel and Northern
Africa. As a result, simulated temperatures are higher, thereby reducing the negative temperature bias found in the Guinean
Coast and Sahel in RegCM3–BATS. In the RegCM3–BATS simulation, warmer temperatures in northern latitudes and wetter soils
near the coast create excessively strong temperature and moist static energy gradients, which shifts the African Easterly
Jet further north than observed. In the RegCM3–CLM3 simulation, the migration and position of the African Easterly Jet more
closely match reanalysis winds. This improvement is triggered by drier soil conditions in the RegCM3–CLM3 simulation and an
increase in evapotranspiration per unit precipitation. These results indicate that atmosphere–land surface coupling has the
ability to impact regional-scale circulation and precipitation in regions exhibiting strong hydroclimatic gradients. 相似文献
994.
A theoretical requirement of the Interaction by Exchange with the Conditional Mean (IECM) micromixing model is that the mean concentration field produced by it must be consistent with the mean concentration field produced by a traditional Lagrangian stochastic (LS) marked particle model. We examine the violation of this requirement that occurs in a coupled LS–IECM model when unrealistically high particle velocities occur. No successful strategy was found to mitigate the effects of these rogue trajectories. It is our hope that this work will provide renewed impetus for investigation into rogue trajectories and methods to eliminate them from LS models. 相似文献
995.
Atmospheric stability effects on the dissimilarity between the turbulent transport of momentum and scalars (water vapour and
temperature) are investigated in the neutral and unstable atmospheric surface layers over a lake and a vineyard. A decorrelation
of the momentum and scalar fluxes is observed with increasing instability. Moreover, different measures of transport efficiency
(correlation coefficients, efficiencies based on quadrant analysis and bulk transfer coefficients) indicate that, under close
to neutral conditions, momentum and scalars are transported similarly whereas, as the instability of the atmosphere increases,
scalars are transported increasingly more efficiently than momentum. This dissimilarity between the turbulent transport of
momentum and scalars under unstable conditions concurs with, and is likely caused by, a change in the topology of turbulent
coherent structures. Previous laboratory and field studies report that under neutral conditions hairpin vortices and hairpin
packets are present and dominate the vertical fluxes, while under free-convection conditions thermal plumes are expected.
Our results (cross-stream vorticity variation, quadrant analysis and time series analysis) are in very good agreement with
this picture and confirm a change in the structure of the coherent turbulent motions under increasing instability, although
the exact structure of these motions and how they are modified by stability requires further investigation based on three-dimensional
flow data. 相似文献
996.
Two mathematical models are proposed detailing the influence of ocean spray on vertical momentum transport under high-wind
conditions associated with a hurricane or severe storm. The first model is based on a turbulent kinetic energy (TKE) equation
and accounts for the so-called lubrication effect due to the reduction of turbulence intensity. The second model is based
on Monin–Obukhov similarity (MOS) and uses available experimental data. It is demonstrated that the flow acceleration is negligible
for wind speeds below a certain critical value due to the fact that the spray volume concentration is low for such speeds.
For wind speeds higher than the critical value, the spray concentration rapidly increases, which results in significant flow
acceleration. Both models produce qualitatively similar results for all turbulent flow parameters considered. It was found
that the MOS-based model tends to predict a noticeably stronger lubrication effect than the TKE-based model, especially for
lower wind speeds. The results of model calculations are in very good agreement with available experimental data for the spray
production values near the upper bound. It is also shown that neither the value of the turbulent Schmidt number in the TKE-based
model nor the choice of a stability profile function affects the spray-laden flow dynamics significantly. 相似文献
997.
Rajani Nair Asha A. Juwarkar Tushar Wanjari S. K. Singh T. Chakrabarti 《Climatic change》2011,106(4):609-619
The micrometeorological technique of eddy covariance is a powerful tool for characterizing the carbon (C) budget of terrestrial
ecosystems. Eddy covariance method was used for estimating Net Ecosystem Exchange (NEE) of carbon dioxide between atmosphere
and revegetated manganese mine spoil dump at Gumgaon, India. In this paper, we analyzed the diel CO2 flux pattern and its response to various physical environmental conditions. The carbon balance of terrestrial ecosystems
is particularly sensitive to climatic changes. Study of diel pattern of CO2 flux showed that carbon uptake was dependent on sunlight. Effect of temperature and latent heat on the CO2 flux showed that rate of CO2 uptake increased proportionally, but later declined due to various factors like stomatal response, high evaporative demand,
circadian rhythm and/or a combination of all three. Net ecosystem production of revegetated land was found to be 28.196 KgC/ha/day
whereas average net carbon release by the ecosystem, through respiration was observed to be 5.433 KgC/ha/day. Thus, quantifying
net carbon (C) storage in degraded land is a necessary step in the validation of carbon sequestration estimates and in assessing
the possible role of these ecosystems in offsetting adverse impacts of fossil fuel emissions. 相似文献
998.
Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore. Part II: Typhoon Intensity and Track 下载免费PDF全文
The impact of cloud microphysical processes on the simulated intensity and track of Typhoon Rananim is discussed and analyzed
in the second part of this study. The results indicate that when the cooling effect due to evaporation of rain water is excluded,
the simulated 36-h maximum surface wind speed of Typhoon Rananim is about 7 m s−1 greater than that from all other experiments; however, the typhoon landfall location has the biggest bias of about 150 km
against the control experiment. The simulated strong outer rainbands and the vertical shear of the environmental flow are
unfavorable for the deepening and maintenance of the typhoon and result in its intensity loss near the landfall. It is the
cloud microphysical processes that strengthen and create the outer spiral rainbands, which then increase the local convergence
away from the typhoon center and prevent more moisture and energy transport to the inner core of the typhoon. The developed
outer rainbands are supposed to bring dry and cold air mass from the middle troposphere to the planetary boundary layer (PBL).
The other branch of the cold airflow comes from the evaporation of rain water itself in the PBL while the droplets are falling.
Thus, the cut-off of the warm and moist air to the inner core and the invasion of cold and dry air to the eyewall region are
expected to bring about the intensity reduction of the modeled typhoon. Therefore, the deepening and maintenance of Typhoon
Rananim during its landing are better simulated through the reduction of these two kinds of model errors. 相似文献
999.
LANG Xianmei 《Acta Meteorologica Sinica》2011,25(5):682-690
In this paper, seasonal prediction of spring dust weather frequency (DWF) in Beijing during 1982-2008 has been performed. First, correlation analyses are conducted to identify antecedent climate signals during last winter that are statistically significantly related to spring DWF in Beijing. Then, a seasonal prediction model of spring DWF in Beijing is established through multivariate linear regression analysis, in which the systematic error between the result of original prediction model and the observation, averaged over the last 10 years, is corrected. In addition, it is found that climate signals occurring synchronously with spring dust weather, particularly meridional wind at 850 hPa over western Mongolian Plateau, are also linked closely to spring DWF in Beijing. As such, statistical and dynamic prediction approaches should be combined to include these synchronous predictors into the prediction model in the real-time operational prediction, so as to further improve the prediction accuracy of spring DWF in Beijing, even over North China. However, realizing such a prediction idea in practice depends essentially on the ability of climate models in predicting key climate signals associated with spring DWF in Beijing. 相似文献
1000.