Chemical precipitation is a useful technology as a pretreatment to treat mature landfill leachate with high concentrations of ammonium-nitrogen （NH＋-N） and refractory organic compounds. Orthogonal experiments and f...Chemical precipitation is a useful technology as a pretreatment to treat mature landfill leachate with high concentrations of ammonium-nitrogen （NH＋-N） and refractory organic compounds. Orthogonal experiments and factorial experiments were carried out to determine the optimal conditions enhancing the magnesium ammonium phosphate （MAP） precipitation process, and the experi- mental results demonstrated that the removal rate of NH＋ -N was more than 85% when MgO and NaHEPO4.2H20 were applied as external sources of magnesium and phosphorous under the optimal conditions that molar ratio n（Mg）：n（N）：n（P） = 1.4：1：0.8, reaction time 60 min, original pH of leachate and settling time 30 min. In the precipitation process, pH could be maintained at the optimal range of 8-9.5 because MgO could release hydroxide ions to consume hydrogen ions. Calcium ions and carbonate ions existed in the leachate could affect the precipitation process, which resulted in the decrease of NH＋-N removal efficiency. The residues of MAP sediments decomposed by heating under alkaline condi- tions can be reused as the sources of phosphorous and magnesium for the removal of high concentrations of NH4＋ -N, and up to 90% of ammonium could be released under molar ratio of n[OH]：n[MAP] = 2.5： 1, heating temperature 90℃ and heating time 2h.展开更多
内循环降水率是本地蒸发产生的降水与总降水量的比值,可以表征陆气相互作用的强度。本研究使用准等熵拉格朗日后向轨迹追踪模型(Quasi-isentropic backward trajectory,QIBT),基于全球陆面数据同化产品(Global Land Data Assimilation S...内循环降水率是本地蒸发产生的降水与总降水量的比值,可以表征陆气相互作用的强度。本研究使用准等熵拉格朗日后向轨迹追踪模型(Quasi-isentropic backward trajectory,QIBT),基于全球陆面数据同化产品(Global Land Data Assimilation Systems,GLDAS)的降水和蒸发数据,以及ERA-Interim再分析资料(ERAI),选取降水量与气候平均态相当的2001年,研究了青藏高原内循环降水率。其次,使用2001年ERAI降水和蒸发数据替换GLDAS数据,分析地表数据不确定性对内循环降水率的影响,最后,选取30年降水和蒸发量的极端情况,探讨了极端干湿年对内循环降水率的影响。结果表明,青藏高原内循环降水率东南部小于西北部,年平均内循环降水率为0.42。极端干年大于2001年,极端湿年小于2001年。使用再分析资料的降水和蒸发数据后,内循环降水率减小为0.28,与再分析资料对青藏高原降水量的高估有关。展开更多
Coupled hydrological and atmospheric model- ing is an effective tool for providing advanced flood forecasting. However, the uncertainties in precipitation forecasts are still considerable. To address uncertainties, a ...Coupled hydrological and atmospheric model- ing is an effective tool for providing advanced flood forecasting. However, the uncertainties in precipitation forecasts are still considerable. To address uncertainties, a one-way coupled atmospheric-hydrological modeling sys- tem, with a combination of high-resolution and ensemble precipitation forecasting, has been developed. It consists of three high-resolution single models and four sets of ensemble forecasts from the THORPEX Interactive Grande Global Ensemble database. The former provides higher forecasting accuracy, while the latter provides the range of forecasts. The combined precipitation forecasting was then implemented to drive the Chinese National Flood Forecasting System in the 2007 and 2008 Huai River flood hindcast analysis. The encouraging results demonstrated that the system can clearly give a set of forecasting hydrographs for a flood event and has a promising relative stability in discharge peaks and timing for warning purposes. It not only gives a deterministic prediction, but also generates probability forecasts. Even though the signal was not persistent until four days before the peak discharge was observed in the 2007 flood event, the visualization based on threshold exceedance provided clear and concise essential warning information at an early stage. Forecasters could better prepare for the possibility of a flood at an early stage, and then issue an actual warning if the signal strengthened. This process may provide decision support for civil protection authorities. In future studies, different weather forecasts will be assigned various weight coefficients to represent the covariance of predictors and the extremes of distributions.展开更多
Based on the extreme forecast index (EFI) of ECMWF, the “observed” EFI (OEFI) of observation is defined and the EFI is calibrated. Then the EFI equivalent percentile (EFIEP) and EFI equivalent quantile (EFIEQ) are d...Based on the extreme forecast index (EFI) of ECMWF, the “observed” EFI (OEFI) of observation is defined and the EFI is calibrated. Then the EFI equivalent percentile (EFIEP) and EFI equivalent quantile (EFIEQ) are designed to forecast the daily extreme precipitation quantitatively. The formulation indicates that the EFIEP is correlated not only to the EFI but also to the proportion of no precipitation. This characteristic is prominent as two areas with nearly same EFIs but different proportions of no precipitation. Cases study shows that the EFIEP can forecast reliable percentile of daily precipitation and 100% percentiles are forecasted for over max extreme events. The EFIEQ is a considerable tool for quantitative precipitation forecast (QPF). Compared to the probabilistic forecast of ensemble prediction system (EPS), it is quantitative and synthesizes the advantage of extreme precipitation location forecast of EPS. Using the observations of 2311 stations of China in 2016 to verify the EFIEP and EFIEQ, the results show that the forecast biases are around 1. The threat scores (TS) for 20 years return period events are about 0.21 and 0.07 for 36 and 180 hours lead times respectively. The equivalent threat scores (ETS) are all larger than 0 and nearly equal to the TS. The TS for heavy rainfall are 0.23 and 0.07 for 36 and 180 lead times respectively. The scores are better than those of high resolution deterministic model (HRDet) and show significant forecast skills for quantitative forecast of extreme daily precipitation.展开更多
Aerosol-cloud-radiation interactions represent one of the largest uncertainties in the current climate assessment. Much of the complexity arises from the non-monotonic responses of clouds, precipitation and radiative ...Aerosol-cloud-radiation interactions represent one of the largest uncertainties in the current climate assessment. Much of the complexity arises from the non-monotonic responses of clouds, precipitation and radiative fluxes to aerosol perturbations under various meteorological conditions. In this study, an aerosol-aware WRF model is used to investigate the microphysical and radiative effects of aerosols in three weather systems during the March 2000 Cloud Intensive Observational Period campaign at the US Southern Great Plains. Three simulated cloud ensembles include a low-pressure deep convective cloud system, a collection of less-precipitating stratus and shallow cumulus, and a cold frontal passage. The WRF simulations are evaluated by several ground-based measurements. The microphysical properties of cloud hydrometeors, such as their mass and number concentrations, generally show monotonic trends as a function of cloud condensation nuclei concentrations. Aerosol radiative effects do not influence the trends of cloud microphysics, except for the stratus and shallow cumulus cases where aerosol semi-direct effects are identified. The precipitation changes by aerosols vary with the cloud types and their evolving stages, with a prominent aerosol invigoration effect and associated enhanced precipitation from the convective sources. The simulated aerosol direct effect suppresses precipitation in all three cases but does not overturn the aerosol indirect effect. Cloud fraction exhibits much smaller sensitivity （typically less than 2%） to aerosol perturbations, and the responses vary with aerosol concentrations and cloud regimes. The surface shortwave radiation shows a monotonic decrease by increasing aerosols, while the magnitude of the decrease depends on the cloud type.展开更多
The effect of kinetics and shape factor on barium sulfate precipitation in a continuous stirred tank has been investigated numerically through solving the standard momentum and mass transport equations in combination ...The effect of kinetics and shape factor on barium sulfate precipitation in a continuous stirred tank has been investigated numerically through solving the standard momentum and mass transport equations in combination with the moment equations for crystal population balance.The numerical method was validated with the literature data.The simulated results include the distribution of the local supersaturation ratio in the reactor,the mean crystal size,and the coefficient of variation.The simulation results show that the value of shape factor used in the model affected greatly the mean crystal size and the moments of the crystal size distribution.The influence of the kinetic expressions on the simulation is also analyzed.It is important to investigate the relationship of the shape factor with the precipitator type and other operation conditions to obtain reliable simulation results and suitable kinetic equations of crystal nucleation and growth rates.展开更多
文摘Chemical precipitation is a useful technology as a pretreatment to treat mature landfill leachate with high concentrations of ammonium-nitrogen （NH＋-N） and refractory organic compounds. Orthogonal experiments and factorial experiments were carried out to determine the optimal conditions enhancing the magnesium ammonium phosphate （MAP） precipitation process, and the experi- mental results demonstrated that the removal rate of NH＋ -N was more than 85% when MgO and NaHEPO4.2H20 were applied as external sources of magnesium and phosphorous under the optimal conditions that molar ratio n（Mg）：n（N）：n（P） = 1.4：1：0.8, reaction time 60 min, original pH of leachate and settling time 30 min. In the precipitation process, pH could be maintained at the optimal range of 8-9.5 because MgO could release hydroxide ions to consume hydrogen ions. Calcium ions and carbonate ions existed in the leachate could affect the precipitation process, which resulted in the decrease of NH＋-N removal efficiency. The residues of MAP sediments decomposed by heating under alkaline condi- tions can be reused as the sources of phosphorous and magnesium for the removal of high concentrations of NH4＋ -N, and up to 90% of ammonium could be released under molar ratio of n[OH]：n[MAP] = 2.5： 1, heating temperature 90℃ and heating time 2h.
文摘内循环降水率是本地蒸发产生的降水与总降水量的比值,可以表征陆气相互作用的强度。本研究使用准等熵拉格朗日后向轨迹追踪模型(Quasi-isentropic backward trajectory,QIBT),基于全球陆面数据同化产品(Global Land Data Assimilation Systems,GLDAS)的降水和蒸发数据,以及ERA-Interim再分析资料(ERAI),选取降水量与气候平均态相当的2001年,研究了青藏高原内循环降水率。其次,使用2001年ERAI降水和蒸发数据替换GLDAS数据,分析地表数据不确定性对内循环降水率的影响,最后,选取30年降水和蒸发量的极端情况,探讨了极端干湿年对内循环降水率的影响。结果表明,青藏高原内循环降水率东南部小于西北部,年平均内循环降水率为0.42。极端干年大于2001年,极端湿年小于2001年。使用再分析资料的降水和蒸发数据后,内循环降水率减小为0.28,与再分析资料对青藏高原降水量的高估有关。
基金This work is supported by the Foundation for the Author of National Excellent Doctoral Dissertation of PR China （Grant No. 201161）, the Program for New Century Excellent Talents in University （Grant No. NCET-12-0842）, the Special Public Sector Research Program of Ministry of Water Resources （Grant Nos. 201301040, 201401008, and 201301070）, the Natural Science Foundation of Jiangsu Province of China （Grant No. BK20131368）, and the National Water Pollution Control and Management Technology Project of China （Grant No. 2012ZX07101-010）.
文摘Coupled hydrological and atmospheric model- ing is an effective tool for providing advanced flood forecasting. However, the uncertainties in precipitation forecasts are still considerable. To address uncertainties, a one-way coupled atmospheric-hydrological modeling sys- tem, with a combination of high-resolution and ensemble precipitation forecasting, has been developed. It consists of three high-resolution single models and four sets of ensemble forecasts from the THORPEX Interactive Grande Global Ensemble database. The former provides higher forecasting accuracy, while the latter provides the range of forecasts. The combined precipitation forecasting was then implemented to drive the Chinese National Flood Forecasting System in the 2007 and 2008 Huai River flood hindcast analysis. The encouraging results demonstrated that the system can clearly give a set of forecasting hydrographs for a flood event and has a promising relative stability in discharge peaks and timing for warning purposes. It not only gives a deterministic prediction, but also generates probability forecasts. Even though the signal was not persistent until four days before the peak discharge was observed in the 2007 flood event, the visualization based on threshold exceedance provided clear and concise essential warning information at an early stage. Forecasters could better prepare for the possibility of a flood at an early stage, and then issue an actual warning if the signal strengthened. This process may provide decision support for civil protection authorities. In future studies, different weather forecasts will be assigned various weight coefficients to represent the covariance of predictors and the extremes of distributions.
文摘Based on the extreme forecast index (EFI) of ECMWF, the “observed” EFI (OEFI) of observation is defined and the EFI is calibrated. Then the EFI equivalent percentile (EFIEP) and EFI equivalent quantile (EFIEQ) are designed to forecast the daily extreme precipitation quantitatively. The formulation indicates that the EFIEP is correlated not only to the EFI but also to the proportion of no precipitation. This characteristic is prominent as two areas with nearly same EFIs but different proportions of no precipitation. Cases study shows that the EFIEP can forecast reliable percentile of daily precipitation and 100% percentiles are forecasted for over max extreme events. The EFIEQ is a considerable tool for quantitative precipitation forecast (QPF). Compared to the probabilistic forecast of ensemble prediction system (EPS), it is quantitative and synthesizes the advantage of extreme precipitation location forecast of EPS. Using the observations of 2311 stations of China in 2016 to verify the EFIEP and EFIEQ, the results show that the forecast biases are around 1. The threat scores (TS) for 20 years return period events are about 0.21 and 0.07 for 36 and 180 hours lead times respectively. The equivalent threat scores (ETS) are all larger than 0 and nearly equal to the TS. The TS for heavy rainfall are 0.23 and 0.07 for 36 and 180 lead times respectively. The scores are better than those of high resolution deterministic model (HRDet) and show significant forecast skills for quantitative forecast of extreme daily precipitation.
基金support provided by NASA ROSES14-ACMAPNSF (Award No. 1700727)+1 种基金supported by the US DOE ASR programsupport of the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA
文摘Aerosol-cloud-radiation interactions represent one of the largest uncertainties in the current climate assessment. Much of the complexity arises from the non-monotonic responses of clouds, precipitation and radiative fluxes to aerosol perturbations under various meteorological conditions. In this study, an aerosol-aware WRF model is used to investigate the microphysical and radiative effects of aerosols in three weather systems during the March 2000 Cloud Intensive Observational Period campaign at the US Southern Great Plains. Three simulated cloud ensembles include a low-pressure deep convective cloud system, a collection of less-precipitating stratus and shallow cumulus, and a cold frontal passage. The WRF simulations are evaluated by several ground-based measurements. The microphysical properties of cloud hydrometeors, such as their mass and number concentrations, generally show monotonic trends as a function of cloud condensation nuclei concentrations. Aerosol radiative effects do not influence the trends of cloud microphysics, except for the stratus and shallow cumulus cases where aerosol semi-direct effects are identified. The precipitation changes by aerosols vary with the cloud types and their evolving stages, with a prominent aerosol invigoration effect and associated enhanced precipitation from the convective sources. The simulated aerosol direct effect suppresses precipitation in all three cases but does not overturn the aerosol indirect effect. Cloud fraction exhibits much smaller sensitivity （typically less than 2%） to aerosol perturbations, and the responses vary with aerosol concentrations and cloud regimes. The surface shortwave radiation shows a monotonic decrease by increasing aerosols, while the magnitude of the decrease depends on the cloud type.
基金Financial support from the National Natural Science Foundation of China(Grant Nos.20236050,50404009 and 50134020)the National Basic Research Priorities Program(No.2004CB217604)the National High Technology Research and Development Program of China(Grant No.2007AA060904)is gratefully acknowledged.
文摘The effect of kinetics and shape factor on barium sulfate precipitation in a continuous stirred tank has been investigated numerically through solving the standard momentum and mass transport equations in combination with the moment equations for crystal population balance.The numerical method was validated with the literature data.The simulated results include the distribution of the local supersaturation ratio in the reactor,the mean crystal size,and the coefficient of variation.The simulation results show that the value of shape factor used in the model affected greatly the mean crystal size and the moments of the crystal size distribution.The influence of the kinetic expressions on the simulation is also analyzed.It is important to investigate the relationship of the shape factor with the precipitator type and other operation conditions to obtain reliable simulation results and suitable kinetic equations of crystal nucleation and growth rates.
