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1.
Several studies have suggested that geostatistical techniques could be employed to reduce overall transactions costs associated with contracting for soil C credits by increasing the efficacy of sampling protocols used to measure C-credits. In this paper, we show how information about the range of spatial autocorrelation can be used in a measurement scheme to reduce the size of the confidence intervals that bound estimates of the mean number of C-credits generated per hectare. A tighter confidence interval around the mean number of C-credits sequestered could increase producer payments for each hectare enrolled in a contract to supply C-credits. An empirical application to dry land cropping systems in three regions of Montana shows that information about the spatial autocorrelation exhibited by soil C could be extremely valuable for reducing transactions costs associated with contracts for C-credits but the benefits are not uniform across all regions or cropping systems. Accounting for spatial autocorrelation greatly reduced the standard errors and narrowed the confidence intervals associated with sample estimates of the mean number of C-credits produced per hectare. For the payment mechanism considered in this paper, tighter confidence intervals around the mean number of C-credits created per hectare enrolled could increase producer payments by more than 100 percent under a C-contract.  相似文献
2.
Changes in climate are expected to lead to changes in the characteristics extreme rainfall frequency and intensity. In this study, we propose an integrated approach to explore potential changes in intensity-duration-frequency (IDF) relationships. The approach incorporates uncertainties due to both the short simulation periods of regional climate models (RCMs) and the differences in IDF curves derived from multiple RCMs in the North American Regional Climate Change Assessment Program (NARCCAP). The approach combines the likelihood of individual RCMs according to the goodness of fit between the extreme rainfall intensities from the RCMs’ historic runs and those from the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) data set and Bayesian model averaging (BMA) to assess uncertainty in IDF predictions. We also partition overall uncertainties into within-model uncertainty and among-model uncertainty. Results illustrate that among-model uncertainty is the dominant source of the overall uncertainty in simulating extreme rainfall for multiple locations in the U.S., pointing to the difficulty of predicting future climate, especially extreme rainfall regimes. For all locations a more intense extreme rainfall occurs in future climate; however the rate of increase varies among locations.  相似文献
3.
Subfossil pollen and plant macrofossil data derived from 14C-dated sediment profiles can provide quantitative information on glacial and interglacial climates. The data allow climate variables related to growing-season warmth, winter cold, and plant-available moisture to be reconstructed. Continental-scale reconstructions have been made for the mid-Holocene (MH, around 6 ka) and Last Glacial Maximum (LGM, around 21 ka), allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change. The synthesis of the available MH and LGM climate reconstructions and their uncertainties, obtained using modern-analogue, regression and model-inversion techniques, is presented for four temperature variables and two moisture variables. Reconstructions of the same variables based on surface-pollen assemblages are shown to be accurate and unbiased. Reconstructed LGM and MH climate anomaly patterns are coherent, consistent between variables, and robust with respect to the choice of technique. They support a conceptual model of the controls of Late Quaternary climate change whereby the first-order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance.  相似文献
4.
We use a state-of-the-art 3-dimensional coupled model to investigate the relative impact of long term variations in the Holocene insolation forcing and of a freshwater release in the North Atlantic. We show that insolation has a greater effect on seasonality and La Ni?a events and is the major driver of sea surface temperature changes. In contrast, the variations in precipitation reflect changes in El Ni?o events. The impact of ice-sheet melting may have offset the impact of insolation on El Ni?o Southern Oscillation variability at the beginning of the Holocene. These simulations provide a coherent framework to refine the interpretation of proxy data and show that changes in seasonality may bias the projection of relationships established between proxy indicators and climate variations in the east Pacific from present day records.  相似文献
5.
缪群 《大气科学进展》2013,30(4):1025-1038
Data from in situ probes and a vertically-pointing mm-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study (Geerts et al., 2010) has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide (AgI) nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming (the Unites States), each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Composite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts (about 610 m above the mountain peak) as a significant increase in the ice crystal concentration in all size bins. The seeding effect appears short-lived as it is not apparent just downwind of the crest.  相似文献
6.
The CloudSat satellite data from June 2006 to April 2011 are used to investigate the characteristics of cloud vertical profiles over East Asia(20°-50°N,80°-120°E),with particular emphasis on the profiles of precipitative clouds in comparison with those of nonprecipitative clouds,as well as the seasonal variations of these profiles.There are some obvious differences between the precipitative and nonprecipitative cloud profiles.Generally,precipitative clouds mainly locate below 8 km with radar reflectivity in the range of-20 to 15 dBZ and maximum values appearing within 2-4-km height,and the clouds usually reach the ground;while nonprecipitative clouds locate in the layers of 4-12 km with radar reflectivity between-28 and 0 dBZ and maximum values within 8-10-km height.There are also some differences among the liquid precipitative,solid precipitative,and possible drizzle precipitative cloud profiles.In precipitative clouds,radar reflectivity increases rapidly from 11 to 7 km in vertical,implying that condensation and collision-coalescence processes play a crucial role in the formation of large-size drops.The frequency distribution of temperature at-15℃ is consistent with the highest frequency of radar reflectivity in solid precipitative clouds,which suggests that the temperatures near-15℃ are conductive to deposition and accretion processes.The vertical profiles of liquid precipitative clouds show almost the same distributions in spring,summer,and autumn but with differences in winter at mainly lower levels.In contrast,the vertical profiles of solid precipitative clouds change from spring to winter with an alternate double and single high-frequency core,which is consistent with variations of the frequency distribution of temperature at-15℃.The vertical profiles of nonprecipitative clouds show a little change with season.The observations also show that the precipitation events over East Asia are mostly related to deep convective clouds and nimbostratus clouds.These results are expected to be useful for evaluation of weather and climate models and for improvement of microphysical parameterizations in numerical models.  相似文献
7.
利用近5年(2006年6月—2011年4月)的Cloudsat卫星资料分析了东亚大陆云垂直结构特征。结果表明:(1)降水(文中可降水是根据观测到的可降水粒子信息计算到达地面的降水,并不是指地面观测到的实际降水)云和非降水云的雷达反射率(回波)垂直分布存在一定差异,除降水云反射率通常接地外,降水云主要集中在8 km以下,反射率通常为-20—15dBz,非降水云主要集中在4—12 km,反射率为-28—0 dBz;降水云雷达反射率频数大值中心在2 4 km,对应的雷达反射率为0—10 dBz,而非降水云出现在8—10 km,且对应的雷达反射率为-26—-24 dBz;(2)从雷达反射率廓线来看,降水云中雷达反射率随高度的变化先增强后减弱,而非降水云几乎不变;(3)液态降水云、固态降水云和毛毛雨降水云反射率的垂直分布明显不同;(4)液态降水云自11至7 km雷达反射率迅速增强,表明此高度是粒子快速增长的优势空间;(5)固态降水云中-15℃温度频数分布与雷达反射率频数大值中心有很好的对应关系,表明在-15℃附近的条件下冰相粒子凝华-碰冻是粒子增长的优势过程;(6)云的垂直结构随着季节变更而变化,降水云春季、夏季和秋季的雷达反射率垂直分布变化不明显,而冬季主要在低层;固态降水云的垂直分布频数大值中心从春季至冬季呈"双-单"中心交替变化,且与云中-15℃频数分布变化一致;非降水云雷达反射率垂直分布没有明显的季节变化;(7)深对流云和雨层云是形成降水粒子的主要云型。  相似文献
8.
In this study,the mechanisms underlying the decadal variability of late spring precipitation in South China are investigated by using the latest Community Earth System Model version 1 (CESM1).We aim to unravel the effects of different climate forcing agents such as aerosols and greenhouse gases (GHGs) on the decadal variation of precipitation,based on transient experiments from pre-industry (for year 1850) to present-day (for year 2000).Our results reveal that:(1) CESM1 can reproduce the climatological features of atmospheric circulation and precipitation for the late spring in South China; (2) only simulations including the forcing of anthropogenic aerosols can reproduce the observed decreasing trend of late spring precipitation from 1950-2000 in South China; (3) aerosols affect the decadal change of precipitation mainly by altering the large-scale atmospheric circulation,and to a less extent by increasing the lower-tropospheric stability to inhibit the convective precipitation; and (4) in comparison,other climate forcing agents such as GHGs have much smaller effects on the decadal change of spring precipitation in South China.  相似文献
9.
Summary The time-dependent motion of long ridges through a linearly stratified fluid otherwise at rest is investigated in a series of laboratory experiments. Similarity conditions for relating such flows to the atmosphere are deduced from the equations of motion and boundary conditions for the respective systems.Experiments concerning end-wall effects in towing experiments with linearly stratified fluid systems are conducted. For obstacles extending across the entire width of the tow tank it is shown that the upstream conditions are continually changing so that a final steady state motion may never be realized. Isolated topographies are shown to induce significantly less effect on the far upstream fluid motions. Case studies for the flow past long ridges for which the motion at large times is to be that of single, double and triple mode lee-waves and breaking lee vortices are conducted for impulsively started and uniformly accelerated and decelerated obstacle transverses. The final flow configuration under certain situations is shown to be relatively insensitive to the starting conditions. In other cases the final flow can be highly dependent on the time history of the ridge traverse through the tank. For example, for the case in which a breaking lee vortex is expected as the final flow, small initial uniform accelerations from a zero velocity lead to the formation of a strong rotor along the free surface of the tank and in the lee of the obstacle. This rotor is maintained in an approximate equilibrium position as the ridge speed reaches a value for which a breaking lee vortex (having no rotor) should be expected; i.e., the type of flow obtained for impulsively started or rapidly accelerating ridges, other parameters being fixed.The phenomenon of the oscillation of the structure of the wake flow between a relatively smooth laminar lee-wave pattern and lee waves that break into turbulence is investigated for impulsively started ridges. By defining the parameterN w as the number of waves downstream of the first trough that are clearly identifiable it is shown that the tendency for wake breakdown into turbulence increases with increasing internal Froude number, other parameters being fixed. No definitive period was found relating the alternating nature of the wake between breakdown, into turbulence, relaminarization and so on.With 20 Figures  相似文献
10.
Summary A series of laboratory experiments have been conducted to simulate the dynamical effects of the flow over and around a model Alpine/Pyrenean topography. The experimental study has employed a linearly salt-stratified rotating water channel through which the model topography is towed. Data have been collected for ranges of the similarity parameters (Rossby, Burger, Ekman and Froude numbers and the topography height to fluid depth ratio) which accord with their atmospheric values; only four of these parameters are independent. The ratio of the fluid depth to topography width need not be simulated because it does not appear as an independent parameter in the leading terms of the governing equations and boundary conditions. The results demonstrate the effects of flow direction on the horizontal motion patterns at various heights and numerous system parameter combinations. Vortex shedding is shown to occur for parameter ranges similar to those appropriate for the atmosphere; an empirical relation between the Strouhal and Rossby numbers is obtained and it is shown that the shedding periods is approximately twice the inertial period. The experiments demonstrate the flow splitting occurs in the vicinity of Geneva for both westerly and northwesterly flow. The importance of the Froude number in controlling the conditions under which fluid flows over or around the topography is illustrated, and the occurrence of lee waves for different values of the Froude and Rossby numbers (and different locations and flow directions) is described. Finally, it is shown that the advection of a parent cyclone from west to east along a path north of the Alps can generate a cyclone in the lower levels of the atmosphere in the vicinity of the Gulf of Genoa. It is suggested that these dynamical effects may play a role in triggering a lee cyclone which then might grow by other physical processes.
Einige Labormodelle von Strömungen im Einfluß des Alpen/Pyrenäen-Gebirgskomplexes
Zusammenfassung Es wurden eine Reihe von Laborexperimenten durchgeführt, um die dynamischen Effekte der Strömung über und um ein Modell der Alpen-Pyrenäentopographie zu simulieren. Bei der Experimentaluntersuchung wurde ein mit Salz linear geschichteter rotierender Wasserkanal, durch den das Modellgelände gezogen wird, verwendet. Es wurden Daten für Bereiche der Ähnlichkeitsparameter (Rossby-, Burger-, Ekman- und Froude-Zahl und das Verhältnis Geländehöhe zu Flüssigkeitstiefe) gesammelt entsprechend ihren atmosphärischen Werten. Nur vier von diesen Parametern sind unabhängig. Das Verhältnis der Flüssigkeitstiefe zur Geländebreite braucht nicht simuliert zu werden, weil es in den Haupttermen der bestimmenden Gleichungen und Randbedingungen nicht als unabhängiger Parameter aufscheint. Die Resultate veranschaulichen die Effekte der Strömungsrichtung auf die horizontalen Bewegungsmuster in verschiedenen Höhen und bei zahlreichen Kombinationen von Systemparametern. Es zeigt sich, daß Wirbelablösung in ähnlichen Parameterbereichen vorkommt, wie sie für die Atmosphäre geeignet sind. Man erhält eine empirische Beziehung zwischen der Strouhal- und der Rossby-Zahl und es zeigt sich, daß die Ablösungsperiode annähernd das Doppelte der Trägheitsperiode ausmacht. Die Experimente zeigen, daß Strömungsaufspaltung im Bereich von Genf sowohl für westliche, als auch für nordwestliche Strömungen vorkommt. Weiters wird die Bedeutung der Froude-Zahl für die Kontrolle der Bedingungen, unter welchen die Flüssigkeit über oder um die Topographie fließt, veranschaulicht und das Auftreten von Lee-Wellen für verschiedene Werte der Froude- und der Rossby-Zahl (und verschiedene Stellen und Strömungsrichtungen) beschrieben. Schließlich wird gezeigt, daß die Advektion einer Mutterzyklone von West nach Ost nördlich der Alpen eine Zyklone in den unteren Schichten der Atmosphäre im Bereich des Golfs von Genua erzeugen kann. Es wird darauf hingewiesen, daß diese dynamischen Effekte beim Auslösen einer Lee-Zyklone, welche dann durch andere physikalische Prozesse wachsen könnte, eine Rolle spielen kann.


With 15 Figures  相似文献
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