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A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.However,a significant difference exists in the modeled strengths,particularly in the stratosphere,with those in three of the AGCMs （CCM3,CAM3,and GFS） being four to five times as strong as those in the two other models （GFDL AM2,ECHAM5）.As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic,but also for projecting its future trend.This issue is addressed in the present study through comparing the models＇ climatological mean states and intrinsic variability,particularly those influencing tropospheric signals to propagate upward and reach the stratosphere.The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference.Based on a comparison with observations,it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5,rather than the strong one simulated by the three other models （CCM3,CAM3 and GFS）.In particular,IOW during the past 50 years may have dynamically induced a 1.0℃ warming in the polar lower stratosphere （～100 hPa）,which canceled a fraction of radiative cooling due to ozone depletion. 相似文献
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文章选取多个国外应用广泛、得到公认并且其主要的大气消减过程都有单独的透射率公式的宽广谱太阳辐射机理模型,在理想大气下将各模型的透射率(TR、TO、TUM)以及直接辐射、散射辐射与精确的谱模型SMARTS逐一进行严格的比较、评述。在此基础上选取模型精确度较高的METSTAT模型,对模型中的相对光学质量、臭氧吸收透射率、均一混合气体吸收透射率等存在的缺陷和不足进行逐一修正,获得一个改进的理想大气太阳辐射模型METSTATM。经过严格的比较,METSTATM模型优于其他模型。 相似文献
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Predicting pyrogenic carbon (PyC) or biochar stability from its precursor properties is critical for evaluating and managing terrestrial C stocks. Transmission mode Fourier transform infrared spectroscopy (FTIR) spectroscopy was compared with proximate analysis data and H/C and O/C for predicting C mineralization. PyC produced at 7 different temperatures from 6 different feedstocks, in addition to the original feedstock materials, was incubated for 3 yr at 30 °C in a sand matrix. A C debt or credit ratio was calculated by comparing the C remaining in the incubated PyC sample (accounting for the measured C lost during initial PyC production) to the C remaining in the incubated original feedstock. A value > 1 indicates that more C remains in the PyC than in the original feedstock (credit), while a value < 1 indicates a debt. After 3 yr, PyC produced at 300 °C lost significantly more C than higher temperature PyC material, but significant differences in C loss between PyC produced at temperatures ⩾ 350 °C were not detectable. The best predictor of C loss was a multiple linear regression model using the fractional FTIR signals at 816, 1048, 1374, 1424, 1460, 1590, 1700 and 2925 cm−1 as parameters (R2 0.80, p < 0.0001). After 3 yr, the C debt or credit ratio reached values significantly > 1 for all corn PyC samples and some bull, dairy and poultry PyC samples, resulting in net C credit, while all pine and oak PyC samples remained in debt. This C debt or credit ratio reveals that, depending on the timeline of interest, producing relatively low temperature PyC with less initial C loss can result in greater C savings than producing higher temperature PyC, even though the C remaining after exposure to higher pyrolysis temperatures is more stable. 相似文献
4.
《Quaternary Science Reviews》2007,26(1-2):70-81
We present a collection of high-resolution chemistry and stable isotope records from the plateau of the Greenland ice cap during the cold event 8200 yr ago. Using a composite of four records, the cold event is observed as a 160.5 yr period during which decadal-mean isotopic values were below average, within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period. Four cores in north, south, and central Greenland show differences at decadal and shorter timescales; it is not yet clear if this represents significant spatial differences in response. The results show clear evidence for colder temperatures and a decrease in snow-accumulation rate. However, the changes in chemical concentrations for the ions looked at here are small, suggesting only minor changes in atmospheric circulation for this event. Apart from the decrease in methane concentration, Greenland ice cores give only weak evidence for effects outside the North Atlantic region. 相似文献
5.
《Quaternary Science Reviews》2007,26(17-18):2247-2264
In the semiarid loess regions, slackwater deposition of overbank flooding over the piedmont alluvial plains was episodic and alternated with dust accumulation and soil formation throughout the Holocene. The records of past hydrological events are therefore preserved within the architecture of loess and soils and are protected from subsequent erosion and destruction. Several Holocene loess–soil sequences with the deposits of overbank flooding over the semiarid piedmont alluvial plains in the southeast part of the middle reaches of the Yellow River drainage basin were investigated by field observation, OSL and C14 dating, measurement of magnetic susceptibility, particle-size distribution and chemical elements. This enables the reconstruction of a complete catalog of Holocene overbank flooding events at a watershed scale and an investigation of hydrological response to monsoonal climatic change as well. During the Holocene, there are six episodes of overbank flooding recorded over the alluvial plain. The first occurred at 11,500–11,000 a BP, i.e. the onset of the Holocene. The second took place at 9500–8500 a BP, immediately before the mid-Holocene Climatic Optimum. After an extended geomorphic stability and soil formation, the third overbank flooding episode came at about 3620–3520 a BP, i.e. the late stage of the mid-Holocene Climatic Optimum, and the floodwater inundated and devastated a Bronze-age town of the Xia Culture built on the alluvial plain, and therefore the town was abandoned for a period of ca 100 years. During the late Holocene, the alluvial plain experienced three episodes of overbank flooding at 2420–2170, 1860–1700 and 680–100 a BP, respectively. The occurrence of these overbank flooding episodes corresponds to the anomalous change in monsoonal climate in the middle reaches of the Yellow River drainage basin when rapid climate change or climatic decline occurs. During at least the last four episodes, both extreme floods and droughts occurred and climate departed from its normal condition, which was defined as a balanced change between the northwestern continental monsoon and southeastern maritime monsoon over time. Great floods occurred as a result of extreme rainstorms in summers caused by rare intensive meridianal airflows involving northwestward moving tropical cyclone systems from the Pacific. These results could be applied to improve our understanding of high-resolution climatic change, and of hydrological response to climatic change in the semiarid zones. 相似文献
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In the period 1999–2009 ten-day SPOT-VEGETATION products of the Normalized Difference Vegetation Index (NDVI) and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) at 1 km spatial resolution were used in order to estimate and forecast the wheat yield over Europe. The products were used together with official wheat yield statistics to fine-tune a statistical model for each NUTS2 region, based on the Partial Least Squares Regression (PLSR) method. This method has been chosen to construct the model in the presence of many correlated predictor variables (10-day values of remote sensing indicators) and a limited number of wheat yield observations. The model was run in two different modalities: the “monitoring mode”, which allows for an overall yield assessment at the end of the growing season, and the “forecasting mode”, which provides early and timely yield estimates when the growing season is on-going. Performances of yield estimation at the regional and national level were evaluated using a cross-validation technique against yield statistics and the estimations were compared with those of a reference crop growth model. Models based on either NDVI or FAPAR normalized indicators achieved similar results with a minimal advantage of the model based on the FAPAR product. Best modelling results were obtained for the countries in Central Europe (Poland, North-Eastern Germany) and also Great Britain. By contrast, poor model performances characterize countries as follows: Sweden, Finland, Ireland, Portugal, Romania and Hungary. Country level yield estimates using the PLSR model in the monitoring mode, and those of a reference crop growth model that do not make use of remote sensing information showed comparable accuracies. The largest estimation errors were observed in Portugal, Spain and Finland for both approaches. This convergence may indicate poor reliability of the official yield statistics in these countries. 相似文献
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Numerous land surface models exist for predicting water and energy fluxes in the terrestrial environment. These land surface models have different conceptualizations (i.e., process or physics based), together with structural differences in representing spatial variability, alternate empirical methods, mathematical formulations and computational approach. These inherent differences in modeling approach, and associated variations in outputs make it difficult to compare and contrast land surface models in a straight-forward manner. While model intercomparison studies have been undertaken in the past, leading to significant progress on the improvement of land surface models, additional framework towards identification of model weakness is needed. Given that land surface models are increasingly being integrated with satellite based estimates to improve their prediction skill, it is practical to undertake model intercomparison on the basis of soil moisture data assimilation. Consequently, this study compares two land surface models: the Joint UK Land Environment Simulator (JULES) and the Community Atmosphere Biosphere Land Exchange (CABLE) for soil moisture estimation and associated assessment of model uncertainty. A retrieved soil moisture data set from the Soil Moisture and Ocean Salinity (SMOS) mission was assimilated into both models, with their updated estimates validated against in-situ soil moisture in the Yanco area, Australia. The findings show that the updated estimates from both models generally provided a more accurate estimate of soil moisture than the open loop estimate based on calibration alone. Moreover, the JULES output was found to provide a slightly better estimate of soil moisture than the CABLE output at both near-surface and deeper soil layers. An assessment of the updated membership in decision space also showed that the JULES model had a relatively stable, less sensitive, and more highly convergent internal dynamics than the CABLE model. 相似文献
9.
《Applied Geochemistry》2006,21(5):849-857
The determination of reduced S species in natural waters is particularly difficult due to their high instability and chemical and physical interferences in the current analytical methods. In this paper a new, rapid and reliable analytical procedure is presented, named the Cd–IC method, for their determination as ΣS2− via oxidation to after chemical trapping with an ammonia–cadmium solution that allows precipitation of all the reduced S species as CdS. The S2−–SO4 is analysed by ion-chromatography. The main advantages of this method are: low cost, high stability of CdS precipitate, absence of interferences, low detection limit (0.01 mg/L as SO4 for 10 mL of water) and low analytical error (about 5%). The proposed method has been applied to more than 100 water samples from different natural systems (water discharges and cold wells from volcanic and geothermal areas, crater lakes) in central-southern Italy. 相似文献
10.
Impact of climate change and irrigation technology advancement on agricultural water use in China 总被引：2，自引：0，他引：2
The impact of climate change and irrigation technology advancement on agricultural water use in China is analyzed for the period of 1949–2005. The Palmer Drought Severity Index (PDSI) is adopted to characterize climate change, and the Gross Irrigation Quota (GIQ) is used to examine the relationship between agricultural water use and climate change in China. The results show that the GIQ correlates well with the PDSI in Chinese irrigated areas for the period of 1949–1990. A quantitative relationship between the GIQ and PDSI is statistically regressed; a new GIQ dataset is generated with the PDSI based on this relationship over the period 1949–2005. The generated GIQ data with climate-only information follow the pattern of the actual GIQ for the period 1949–1990. Since 1991, the actual GIQ becomes much smaller than the generated GIQ, indicating that irrigation technology advancement exerts a dominant impact on reducing agricultural water use intensity in China. 相似文献