Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)an...Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.展开更多
Sea spray,which comprises amounts of small ocean droplets,plays a significant role in the air-sea coupling,atmospheric and oceanic dynamics,and climate.However,it remains arduous to arrive at estimates for the efficie...Sea spray,which comprises amounts of small ocean droplets,plays a significant role in the air-sea coupling,atmospheric and oceanic dynamics,and climate.However,it remains arduous to arrive at estimates for the efficiency and accuracy of the sea spray induced air-sea heat and salt fluxes.This is because the microphysical process of sea spray evolution in the air is of extreme complexity.In this study,we iteratively calculated the sea spray induced air-sea heat and salt fluxes at various weather condition.To do so,we implemented one novel wave-steepness-dependent sea spray model into a bulk air-sea fluxes algorithm and utilized other sea spray models as comparisons.Based on the improved wave-dependent bulk turbulent algorithm,we observed that despite the negative contribution of sea spray to the sensible heat fluxes,the sea spray positively contributes to the air-sea latent heat fluxes,leading to an overall increase in the total air-sea heat fluxes.The additional heat fluxes caused by sea spray may be the missing critical process that can clarify the discrepancies observed between measured and modelled Tropical Cyclone’s development and intensification.In addition to heat fluxes,we observed that sea spray has significant impacts on the air-sea salt fluxes.As the sea salt particles are one of the main sources of the atmosphere aerosol,our results imply that sea spray could impact global and regional climate.Thus,given the significance of sea spray on the air-sea boundary layer,sea spray effects need to be considered in studies of air-sea interaction,dynamics of atmosphere and ocean.展开更多
It is crucial to appropriately determine turbulent fluxes in numerical models.Using data collected in East Antarctica from 8 April to 26 November 2016,this study evaluates parameterization schemes for turbulent fluxes...It is crucial to appropriately determine turbulent fluxes in numerical models.Using data collected in East Antarctica from 8 April to 26 November 2016,this study evaluates parameterization schemes for turbulent fluxes over the landfast seaice surface in five numerical models.The Community Noah Land Surface Model with Multi-Parameterizations Options(Noah_mp)best replicates the turbulent momentum flux,while the Beijing Climate System Model(BCC_CSM)produces the optimum sensible and latent heat fluxes.In particular,two critical issues of parameterization schemes,stability functions and roughness lengths,are investigated.Sensitivity tests indicate that roughness lengths play a decisive role in model performance.Based on the observed turbulent fluxes,roughness lengths over the landfast sea-ice surface are calculated.The results,which can provide a basis for setting up model parameters,reveal that the dynamic roughness length(z0m)increases with the increase of frictional velocity(u*)when u*≤0.4 m s^(−1) and fluctuates around 10^(−3 )m when u*>0.4 m s^(−1);thermal roughness length(z0t)is linearly related to the temperature gradient between air and sea-ice surface(ΔT)with a relation of lg(z0t)=−0.29ΔT−3.86;and the mean water vapor roughness length(z0q)in the specific humidity gradient(Δq)range ofΔq≤−0.6 g kg^(−1) is 10^(−6) m,3.5 times smaller than that in the range ofΔq˃−0.6 g kg^(−1).展开更多
We use the High-energy Electron Experiments(HEP)instrument onboard Arase(ERG)to conduct an energy-dependent cross-satellite calibration of electron fluxes measured by the High Energy Particle Detector(HEPD)onboard Fen...We use the High-energy Electron Experiments(HEP)instrument onboard Arase(ERG)to conduct an energy-dependent cross-satellite calibration of electron fluxes measured by the High Energy Particle Detector(HEPD)onboard FengYun-4A(FY-4A)spanning from April 1,2017,to September 30,2019.By tracing the two-dimensional magnetic positions(L,magnetic local time[MLT])of FY-4A at each time,we compare the datasets of the conjugate electron fluxes over the range of 245–894 keV in 6 energy channels for the satellite pair within different sets of L×MLT.The variations in the electron fluxes observed by FY-4A generally agree with the Arase measurements,and the percentages of the ratios of electron flux conjunctions within a factor of 2 are larger than 50%.Compared with Arase,FY-4A systematically overestimates electron fluxes at all 6 energy channels,with the corresponding calibration factors ranging from 0.67 to 0.81.After the cross-satellite calibration,the electron flux conjunctions between FY-4A and Arase show better agreement,with much smaller normalized root mean square errors.Our results provide a valuable reference for the application of FY-4A high-energy electron datasets to in-depth investigations of the Earth’s radiation belt electron dynamics.展开更多
This paper addresses the issue of the formulation of weak solutions to systems of nonlinear hyperbolic conservation laws as integral balance laws.The basic idea is that the“meaningful objects”are the fluxes,evaluate...This paper addresses the issue of the formulation of weak solutions to systems of nonlinear hyperbolic conservation laws as integral balance laws.The basic idea is that the“meaningful objects”are the fluxes,evaluated across domain boundaries over time intervals.The fundamental result in this treatment is the regularity of the flux trace in the multi-dimensional setting.It implies that a weak solution indeed satisfies the balance law.In fact,it is shown that the flux is Lipschitz continuous with respect to suitable perturbations of the boundary.It should be emphasized that the weak solutions considered here need not be entropy solutions.Furthermore,the assumption imposed on the flux f(u)is quite minimal-just that it is locally bounded.展开更多
Because radiation belt electrons can pose a potential threat to the safety of satellites orbiting in space,it is of great importance to develop a reliable model that can predict the highly dynamic variations in outer ...Because radiation belt electrons can pose a potential threat to the safety of satellites orbiting in space,it is of great importance to develop a reliable model that can predict the highly dynamic variations in outer radiation belt electron fluxes.In the present study,we develop a forecast model of radiation belt electron fluxes based on the data assimilation method,in terms of Van Allen Probe measurements combined with three-dimensional radiation belt numerical simulations.Our forecast model can cover the entire outer radiation belt with a high temporal resolution(1 hour)and a spatial resolution of 0.25 L over a wide range of both electron energy(0.1-5.0 MeV)and pitch angle(5°-90°).On the basis of this model,we forecast hourly electron fluxes for the next 1,2,and 3 days during an intense geomagnetic storm and evaluate the corresponding prediction performance.Our model can reasonably predict the stormtime evolution of radiation belt electrons with high prediction efficiency(up to~0.8-1).The best prediction performance is found for~0.3-3 MeV electrons at L=~3.25-4.5,which extends to higher L and lower energies with increasing pitch angle.Our results demonstrate that the forecast model developed can be a powerful tool to predict the spatiotemporal changes in outer radiation belt electron fluxes,and the model has both scientific significance and practical implications.展开更多
The 6351 wrought aluminum alloy and K2TiF6-CaF2-LiCl components were selected as raw materials to fabricate in situ Al3Ti particulate reinforced aluminum alloy at 720℃via direct melt reaction method with electromagne...The 6351 wrought aluminum alloy and K2TiF6-CaF2-LiCl components were selected as raw materials to fabricate in situ Al3Ti particulate reinforced aluminum alloy at 720℃via direct melt reaction method with electromagnetic stirring(EMS).CaF2 and LiCl acted as fluxes to lower the reaction temperature of the system.It is shown that the electromagnetic stirring and fluxes accelerate the emulsion process of K2TiF6.Optical microscopy,scanning electron microscopy,transmission electron microscopy and energy dispersive spectrum were utilized to analyze the microstructure and components of composites.Compared to composites fabricated without EMS and fluxes,the sizes of endogenetic Al3Ti are refined from 10-15μm to 2-4μm,which are often accompanied with silicon element.The morphology of Al3Ti or Al3TiSi0.22 exhibits triangle,quadrilateral and other clumpy patterns. Because of the Ca elements from CaF2,the sizes of Mg2Si decrease from 8-10μm to 1-2μm due to the formation of Ca2Si.展开更多
A novel flux charging method and a crucible quenching method were employed to study the mechanism of solid fluxes refining method regarding the removal of oxide inclusions(Al_2O_3) from molten aluminum. Electrochemica...A novel flux charging method and a crucible quenching method were employed to study the mechanism of solid fluxes refining method regarding the removal of oxide inclusions(Al_2O_3) from molten aluminum. Electrochemical polishing method was adopted to prepare surfaces of the samples. Through experiments, the morphology of the residual solidified flux in the solidified samples as well as the wetting action of the molten flux during refining were observed for the first time. Three wetting regimes denoted by absorbing regime, engulfing regime and penetration regime correlating with the removal of oxide films(the most typical and common oxide inclusions in molten aluminum) were proposed in terms of different types and distributions of oxide films and different size ratios of the molten flux to oxide films. Particularly, from a thermodynamic point of view, for the first time, the penetration regime provided concrete evidence that the practical oxide inclusions can be wet by molten flux under ambient fluid of molten aluminum. A spreading model was proposed, according to which ingredients and size parameters of practical solid fluxes can be optimized.展开更多
Bamboo forest is an important forest type in subtropical China and is characterized by fast growth and high carbon sequestration capacity. However, the dynamics of carbon fluxes during the fast growing period of bambo...Bamboo forest is an important forest type in subtropical China and is characterized by fast growth and high carbon sequestration capacity. However, the dynamics of carbon fluxes during the fast growing period of bamboo shoots and their correlation with environment factors are poorly understood. We measured carbon dioxide exchange and climate variables using open-path eddy covariance methods during the 2011 growing season in a Moso bamboo forest(MB, Phyllostchys edulis) and a Lei bamboo forest(LB, Phyllostachys violascens) in Zhejiang province,China. The bamboo forests were carbon sinks during the growing season. The minimum diurnal net ecosystem exchange(NEE) at MB and LB sites were-0.64 and-0.66 mg C m^(-2) s^(-1), respectively. The minimum monthly NEE, ecosystem respiration(RE), and gross ecosystem exchange(GEE) were-99.3 ± 4.03, 76.2 ±2.46, and^(-1)91.5 ± 4.98 g C m^(-2) month^(-1), respectively,at MB site, compared with-31.8 ± 3.44, 70.4 ± 1.41,and^(-1)57.9 ± 4.86 g C m^(-2) month^(-1), respectively, at LB site. Maximum RE was 92.1 ± 1.32 g C m^(-2) month^(-1) at MB site and 151.0 ± 2.38 g C m^(-2) month^(-1) at LB site.Key control factors varied by month during the growing season, but across the whole growing season, NEE and GEE at both sites showed similar trends in sensitivities to photosynthetic active radiation and vapor pressure deficit,and air temperature had the strongest correlation with RE at both sites. Carbon fluxes at LB site were more sensitive to soil water content compared to those at MB site. Both onyear(years when many new shoots are produced) and offyear(years when none or few new shoots are produced)should be studied in bamboo forests to better understand their role in global carbon cycling.展开更多
As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,rese...As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,reservoirs have important effects on the fluvial transport of material from land to ocean,and inevitably have complex terrain which can complicate and distort the results of seismic surveys.Therefore,there are still some problems need to be resolved in the application of seismic surveys in reservoirs with complex terrain.For this study,the Dongfeng Reservoir located in the upper reaches of the Wujiang River was chosen as an example to test the seismic survey method.Our testing showed that(1)because of the complex underwater terrain,the signal-to-noise ratio of the echo signal in canyon reservoir is low,making it difficult to determine sediment layers thicknesses in some areas;and(2)due to the large spatial heterogeneity of sediment distribution,insufficient density of cross-sections can lead to inaccurate interpolation results.To improve the accuracy of calculations,a mathematical method was used.Ultimately,the total burial mass of sediment was estimated at 2.85 x 107 tons,and the average burial rates of total organic carbon,total phosphorus,and total nitrogen were estimated at 0.194,0.011,and 0.014 g cm-2 year-1,respectively.These values were close to the results of previous studies and hydrographic station data,indicating that seismic survey can be a reliable and efficient method for the mapping of reservoirs.展开更多
To improve the heat transfer capability and the crystallization property of the traditional mold flux, CaF_2 was replaced with B_2O_3. Then, the influences of CeO_2 on the heat transfer and the crystallization of the ...To improve the heat transfer capability and the crystallization property of the traditional mold flux, CaF_2 was replaced with B_2O_3. Then, the influences of CeO_2 on the heat transfer and the crystallization of the CaF_2-bearing mold flux and the new mold flux with 10 wt% B_2O_3 were studied using a slag film heat flux simulator and X-ray diffraction(XRD). The results revealed that the addition of CeO2 reduced the heat transfer by increasing the solid slag thickness and the crystallization of two mold fluxes. However, CeO_2 had less effect on the B_2O_3-containing mold flux compared with the CaF_2-bearing mold flux. According to the analyses, the CeO_2 contents in the CaF_2-bearing mold flux and the B_2O_3-containing mold flux should not exceed 8 wt% and 12 wt%, respectively. Therefore, these experimental results are beneficial to improve and develop the mold flux for casting rare earth alloy steels.展开更多
Atmospheric deposition(dry and wet deposition)is one of the primary sources of chemical inputs to terrestrial ecosystems and replenishes the nutrient pool in forest ecosystems.Precipitation often acts as a primary tra...Atmospheric deposition(dry and wet deposition)is one of the primary sources of chemical inputs to terrestrial ecosystems and replenishes the nutrient pool in forest ecosystems.Precipitation often acts as a primary transporting agent and solvent;thus,nutrient cycles in forests are closely linked to hydrological processes.We collected precipitation data during a growing season to explore variations in nutrient cycling and nutrient balances in the rainfall redistribution process(wet deposition)in a larch plantation in northeast China.We measured nutrient(NO_(3)^(-),PO_(4)^(3−),Cl^(−),K,Ca,Na,and Mg)inputs via bulk precipitation,throughfall and stemfl ow,and used a canopy budget model to estimate nutrient fl uxes via canopy exchange.Our results suggest that the average concentrations of the base cation(K,Ca,Na,and Mg)showed the following order:stemfl ow>throughfall>bulk precipitation.Throughfall and stemfl ow chemistry dramatically fl uctuated over the growing season when net fl uxes(throughfall+stemfl ow—bulk precipitation)of NO−3,PO3−4,SO2−4,Cl−,K,Ca,Na,and Mg were−6.676 kg·ha^(-1),−1.094 kg·ha^(-1),−2.371 kg·ha^(-1),1.975 kg·ha^(-1),0.470 kg·ha^(-1),−5.202 kg·ha^(-1),−0.336 kg·ha^(-1),and 1.397 kg·ha^(-1),respectively.These results suggest that NO−3,PO3−4,SO2−4,Ca,and Na were retained,while Cl−,K,and Mg were washed off by throughfall and stemfl ow.展开更多
The biogeochemical behavior of DIN (dissolved inorganic nitrogen), phosphate and silicate in the Minjiang River estuary is discussed based on data obtained from May, 1990 to Feb., 1991 oceanographic surveys in the are...The biogeochemical behavior of DIN (dissolved inorganic nitrogen), phosphate and silicate in the Minjiang River estuary is discussed based on data obtained from May, 1990 to Feb., 1991 oceanographic surveys in the area. The annual fluxes of nutrients in the Minjiang River estuary were estimated to be 326.8 ×103 t for silicate, 771.0 t for phosphate, 45.7×103 t for DIN (42.1×103 t for nitrate, 3.0×103 t for ammonia. 600 t for nitrite), respectively.展开更多
Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4...Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4)fluxes in wetlands.However,the symbiotic relationship between methanogens and methanotrophs remains unclear.To help close this research gap,we collected and analyzed samples from four soil depths in the Dajiuhu subalpine peatland in January,April,July,and October 2019 and acquired seasonal methane flux data from an eddy covariance(EC)system,and investigated relationships.A phylogenetic molecular ecological networks(pMENs)analysis was used to identify keystone species and the seasonal variations of the co-occurrence patterns of methanogenic and methanotrophic communities.The results indicate that the seasonal variations of the interactions between methanogenic and methanotrophic communities contributed to CH_(4)emissions in wetlands.The keystone species discerned by the network analysis also showed their importance in mediating CH_(4)fluxes.Methane(CH_(4))emissions in wetlands were lowest in spring;during this period,the most complex interactions between microbes were observed,with intense competition among methanogens while methanotrophs demonstrated better cooperation.Reverse patterns manifested themselves in summer when the highest CH_(4)flux was observed.Methanoregula formicica was negatively correlated with CH_(4)fluxes and occupied the largest ecological niches in the spring network.In contrast,both Methanocella arvoryzae and Methylocystaceae demonstrated positive correlations with CH_(4)fluxes and were better adapted to the microbial community in the summer.In addition,soil temperature and nitrogen were regarded as significant environmental factors to CH_(4)fluxes.This study was successful in explaining the seasonal patterns and microbial driving mechanisms of CH_(4)emissions in wetlands.展开更多
The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO-2, NO-3, PO3-4 and SIO4...The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO-2, NO-3, PO3-4 and SIO4-4) were measured in PW and BW in El Mex Bay and surround drains during spring 2010. Nutrient concentrations gradiance in PW with overlying seawater were evaluated according to Fick’s Law. Average inorganic nutrient fluxes were estimated using the pore water gradient concentration across the sediment-water interface. Calculated nutrient fluxes had averages of ﹣7.24, ﹣1.36, ﹣7.86 and ﹣1.33 in El Mex Bay. Additionally, the fluxes in the drains were ﹣34.39, ﹣32.28, ﹣53.20 and ﹣117.6 mg·m﹣2·day﹣1 for NO-3, NO-2, PO3-4 and SIO4-4, respectively. Mineralogical studies of sediment samples by using IR, X-ray analysis were carried out to identify the chemical structure of sediments. The results revealed that calcite, aragonite and quartz are the dominant minerals. On the other hand, differential thermal analysis (DTA) was used to evaluate and discuss different kinetic parameters such as Ea#, ΔG#, ΔH#, ΔS#, Z and Tm support the view of the extra stability of these sediments.展开更多
<div style="text-align:justify;"> In this paper, we study the error estimates for direct discontinuous Galerkin methods based on the upwind-biased fluxes. We use a newly global projection to obtain the...<div style="text-align:justify;"> In this paper, we study the error estimates for direct discontinuous Galerkin methods based on the upwind-biased fluxes. We use a newly global projection to obtain the optimal error estimates. The numerical experiments imply that <em>L</em><sup>2 </sup>norms error estimates can reach to order <em>k</em> + 1 by using time discretization methods. </div>展开更多
Wet deposition was collected in Mexico City (MC), Metropolitan Area of Monterrey (MAM) and El Chico National Park (ECNP), during 2009 and 2010. pH, conductivity, Cl-, , Na+, K+, Ca2+ and Mg2+ were determined. In MC, s...Wet deposition was collected in Mexico City (MC), Metropolitan Area of Monterrey (MAM) and El Chico National Park (ECNP), during 2009 and 2010. pH, conductivity, Cl-, , Na+, K+, Ca2+ and Mg2+ were determined. In MC, sulphate levels were greater than nitrate levels, and NH4 had mixed sources (vehicular emissions and agriculture activities). MAM had markedly alkaline atmospheric deposition, Na+ and Cl-levels were unexpectedly high, especially during hurricane “Alex”. Low pH values were found in ECNP and nitrate concentrations were high, suggesting the influence of a local source (forest fires). Deposition fluxes (Kg.ha-1yr-1) for N-NO3, N-NH4 and S-SO4 were 1.36, 2.74 and 4.84 for MAM;7.27, 0.57 and 4.32 for ECNP;and 5.97, 4.96 and 6.78 for MC, respectively. Nitrogen deposition fluxes in ECNP were high considering that this site is a natural reserve.展开更多
Evapotranspiration acts an important role in hydrologic cycle and water resources planning. But the estimation issue still remains until nowadays. This research attempts to make clear this problem by the following way...Evapotranspiration acts an important role in hydrologic cycle and water resources planning. But the estimation issue still remains until nowadays. This research attempts to make clear this problem by the following way. In a humid region, by applying the Bowen ratio concept and optimum procedure on the soil surface, sensible and latent heat fluxes are estimated using net radiation (Rn) and heat flux into the ground (G). The method uses air temperature and humidity at a single height by reciprocally determining the soil surface temperature (Ts) and the relative humidity (rehs). This feature can be remarkably extended to the utilization. The validity of the method is confirmed by comparing of observed and estimated latent (lE) and sensible heat flux (H) using the eddy covariance method. The hourly change of the lE, H, Ts and rehs on the soil surface, yearly change of lE and H and relationship of estimated lE and H versus observed are clarified. Furthermore, monthly evapotranspiration is estimated from the lE. The research was conducted using hourly data of FLUXNET at a site of Japan, three sites of the United States and two sites of Europe in humid regions having over 1000 mm of annual precipitation.展开更多
The surface exchange of NH<sub>3</sub> and HNO<sub>3</sub> gases over heathland was measured with theaerodynamic gradient method in Leende,the Netherlands during April 25 and May 9,1991.Due tor...The surface exchange of NH<sub>3</sub> and HNO<sub>3</sub> gases over heathland was measured with theaerodynamic gradient method in Leende,the Netherlands during April 25 and May 9,1991.Due toreactions in the system NH<sub>3</sub>,HNO<sub>3</sub> and NH<sub>4</sub>NO<sub>3</sub>,the NH<sub>3</sub> deposition flux is overestimated,whileHNO<sub>3</sub> shows apparent emission fluxes mostly during the field experiment.Results reveal that NH<sub>3</sub>gradients are influenced slightly by HNO<sub>3</sub> and the HNO<sub>3</sub> gradients are strongly controlled by theNH<sub>3</sub>.A clear relationship between NH<sub>3</sub> and HNO<sub>3</sub> gradient is suggested by the Leende experiment.Before the late afternoon,NH<sub>3</sub> deposition gradients will cause HNO<sub>3</sub> upward gradients,meanwhilethe NH<sub>3</sub> gradients themselves will become smaller.After the HNO<sub>3</sub> upward gradient reaches maxi-mum,the NH<sub>3</sub> deposition gradients will be enlarged or the emission gradients depressed,while theHNO<sub>3</sub> upward gradients become smaller.展开更多
基金the National Natural Science Foundation of China(Grant No.U20A2081)West Light Foundation of the Chinese Academy of Sciences(Grant No.xbzg-zdsys-202102)the Second Tibetan Plateau Scientific Expedition and Research(STEP)Project(Grant No.2019QZKK0105).
文摘Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.
基金The support of the US Office of Naval Research Global under contract No.N62909-20-1-2080.
文摘Sea spray,which comprises amounts of small ocean droplets,plays a significant role in the air-sea coupling,atmospheric and oceanic dynamics,and climate.However,it remains arduous to arrive at estimates for the efficiency and accuracy of the sea spray induced air-sea heat and salt fluxes.This is because the microphysical process of sea spray evolution in the air is of extreme complexity.In this study,we iteratively calculated the sea spray induced air-sea heat and salt fluxes at various weather condition.To do so,we implemented one novel wave-steepness-dependent sea spray model into a bulk air-sea fluxes algorithm and utilized other sea spray models as comparisons.Based on the improved wave-dependent bulk turbulent algorithm,we observed that despite the negative contribution of sea spray to the sensible heat fluxes,the sea spray positively contributes to the air-sea latent heat fluxes,leading to an overall increase in the total air-sea heat fluxes.The additional heat fluxes caused by sea spray may be the missing critical process that can clarify the discrepancies observed between measured and modelled Tropical Cyclone’s development and intensification.In addition to heat fluxes,we observed that sea spray has significant impacts on the air-sea salt fluxes.As the sea salt particles are one of the main sources of the atmosphere aerosol,our results imply that sea spray could impact global and regional climate.Thus,given the significance of sea spray on the air-sea boundary layer,sea spray effects need to be considered in studies of air-sea interaction,dynamics of atmosphere and ocean.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFE0106300)the National Natural Science Foundation of China(Grant Nos.42105072,41941009,41922044)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2021A1515012209,2020B1515020025)the China Postdoctoral Science Foundation(Grant Nos.2021M693585)the Norges Forskningsråd(Grant No.328886).
文摘It is crucial to appropriately determine turbulent fluxes in numerical models.Using data collected in East Antarctica from 8 April to 26 November 2016,this study evaluates parameterization schemes for turbulent fluxes over the landfast seaice surface in five numerical models.The Community Noah Land Surface Model with Multi-Parameterizations Options(Noah_mp)best replicates the turbulent momentum flux,while the Beijing Climate System Model(BCC_CSM)produces the optimum sensible and latent heat fluxes.In particular,two critical issues of parameterization schemes,stability functions and roughness lengths,are investigated.Sensitivity tests indicate that roughness lengths play a decisive role in model performance.Based on the observed turbulent fluxes,roughness lengths over the landfast sea-ice surface are calculated.The results,which can provide a basis for setting up model parameters,reveal that the dynamic roughness length(z0m)increases with the increase of frictional velocity(u*)when u*≤0.4 m s^(−1) and fluctuates around 10^(−3 )m when u*>0.4 m s^(−1);thermal roughness length(z0t)is linearly related to the temperature gradient between air and sea-ice surface(ΔT)with a relation of lg(z0t)=−0.29ΔT−3.86;and the mean water vapor roughness length(z0q)in the specific humidity gradient(Δq)range ofΔq≤−0.6 g kg^(−1) is 10^(−6) m,3.5 times smaller than that in the range ofΔq˃−0.6 g kg^(−1).
基金supported by the National Natural Science Foundation of China(Grant Nos.42025404,42188101,42241143,41931073,and 42204160)the National Key R&D Program of China(Grant Nos.2022YFF0503700,2022YFF0503900,and 2021YFA0718600)+1 种基金the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)the Fundamental Research Funds for the Central Universities(Grant Nos.2042022kf1012 and 2042022kf1016).
文摘We use the High-energy Electron Experiments(HEP)instrument onboard Arase(ERG)to conduct an energy-dependent cross-satellite calibration of electron fluxes measured by the High Energy Particle Detector(HEPD)onboard FengYun-4A(FY-4A)spanning from April 1,2017,to September 30,2019.By tracing the two-dimensional magnetic positions(L,magnetic local time[MLT])of FY-4A at each time,we compare the datasets of the conjugate electron fluxes over the range of 245–894 keV in 6 energy channels for the satellite pair within different sets of L×MLT.The variations in the electron fluxes observed by FY-4A generally agree with the Arase measurements,and the percentages of the ratios of electron flux conjunctions within a factor of 2 are larger than 50%.Compared with Arase,FY-4A systematically overestimates electron fluxes at all 6 energy channels,with the corresponding calibration factors ranging from 0.67 to 0.81.After the cross-satellite calibration,the electron flux conjunctions between FY-4A and Arase show better agreement,with much smaller normalized root mean square errors.Our results provide a valuable reference for the application of FY-4A high-energy electron datasets to in-depth investigations of the Earth’s radiation belt electron dynamics.
基金the Institute of Applied Physics and Computational Mathematics,Beijing,for the hospitality and support.The second author is supported by the NSFC(Nos.11771054,12072042,91852207)the Sino-German Research Group Project(No.GZ1465)the National Key Project GJXM92579.
文摘This paper addresses the issue of the formulation of weak solutions to systems of nonlinear hyperbolic conservation laws as integral balance laws.The basic idea is that the“meaningful objects”are the fluxes,evaluated across domain boundaries over time intervals.The fundamental result in this treatment is the regularity of the flux trace in the multi-dimensional setting.It implies that a weak solution indeed satisfies the balance law.In fact,it is shown that the flux is Lipschitz continuous with respect to suitable perturbations of the boundary.It should be emphasized that the weak solutions considered here need not be entropy solutions.Furthermore,the assumption imposed on the flux f(u)is quite minimal-just that it is locally bounded.
基金supported by the National Natural Science Foundation of China (Grant Nos. 42025404, 42188101, and 42241143)the National Key R&D Program of China (Grant Nos. 2022YFF0503700 and 2022YFF0503900)+1 种基金the B-type Strategic Priority Program of the Chinese Academy of Sciences (Grant No. XDB41000000)the Fundamental Research Funds for the Central Universities (Grant No. 2042022kf1012)
文摘Because radiation belt electrons can pose a potential threat to the safety of satellites orbiting in space,it is of great importance to develop a reliable model that can predict the highly dynamic variations in outer radiation belt electron fluxes.In the present study,we develop a forecast model of radiation belt electron fluxes based on the data assimilation method,in terms of Van Allen Probe measurements combined with three-dimensional radiation belt numerical simulations.Our forecast model can cover the entire outer radiation belt with a high temporal resolution(1 hour)and a spatial resolution of 0.25 L over a wide range of both electron energy(0.1-5.0 MeV)and pitch angle(5°-90°).On the basis of this model,we forecast hourly electron fluxes for the next 1,2,and 3 days during an intense geomagnetic storm and evaluate the corresponding prediction performance.Our model can reasonably predict the stormtime evolution of radiation belt electrons with high prediction efficiency(up to~0.8-1).The best prediction performance is found for~0.3-3 MeV electrons at L=~3.25-4.5,which extends to higher L and lower energies with increasing pitch angle.Our results demonstrate that the forecast model developed can be a powerful tool to predict the spatiotemporal changes in outer radiation belt electron fluxes,and the model has both scientific significance and practical implications.
基金Project(2007AA03Z548)supported by the National High-Tech Research and Development Program of ChinaProject(207038)supported by the Key Program of Ministry of Education of China+3 种基金Project(06-D-021)supported by the Talents Peak in Six Key Fields of Jiangsu Province in ChinaProject(07JDG084)supported by the Technical Enablement Foundation for the Super Special Talents of Jiangsu UniversityProject(20071108)supported by the Technical Enablement Foundation of Ministry of Education for the Returned ScholarsProject(20060299006)supported by the PhD Programs Foundation of Ministry of Education of China
文摘The 6351 wrought aluminum alloy and K2TiF6-CaF2-LiCl components were selected as raw materials to fabricate in situ Al3Ti particulate reinforced aluminum alloy at 720℃via direct melt reaction method with electromagnetic stirring(EMS).CaF2 and LiCl acted as fluxes to lower the reaction temperature of the system.It is shown that the electromagnetic stirring and fluxes accelerate the emulsion process of K2TiF6.Optical microscopy,scanning electron microscopy,transmission electron microscopy and energy dispersive spectrum were utilized to analyze the microstructure and components of composites.Compared to composites fabricated without EMS and fluxes,the sizes of endogenetic Al3Ti are refined from 10-15μm to 2-4μm,which are often accompanied with silicon element.The morphology of Al3Ti or Al3TiSi0.22 exhibits triangle,quadrilateral and other clumpy patterns. Because of the Ca elements from CaF2,the sizes of Mg2Si decrease from 8-10μm to 1-2μm due to the formation of Ca2Si.
基金financially supported by the International Science&Technology Cooperation Program of China(No.2015DFR50470)Guangdong Provincial Science&Technology Foundation(No.2015B090926013)
文摘A novel flux charging method and a crucible quenching method were employed to study the mechanism of solid fluxes refining method regarding the removal of oxide inclusions(Al_2O_3) from molten aluminum. Electrochemical polishing method was adopted to prepare surfaces of the samples. Through experiments, the morphology of the residual solidified flux in the solidified samples as well as the wetting action of the molten flux during refining were observed for the first time. Three wetting regimes denoted by absorbing regime, engulfing regime and penetration regime correlating with the removal of oxide films(the most typical and common oxide inclusions in molten aluminum) were proposed in terms of different types and distributions of oxide films and different size ratios of the molten flux to oxide films. Particularly, from a thermodynamic point of view, for the first time, the penetration regime provided concrete evidence that the practical oxide inclusions can be wet by molten flux under ambient fluid of molten aluminum. A spreading model was proposed, according to which ingredients and size parameters of practical solid fluxes can be optimized.
基金supported by Natural Science Foundation of Zhejiang Province(No.LR14C160001)National Natural Science Foundation(No.61190114,31370637,31500520)+3 种基金Joint Research fund of Department of Forestry of Zhejiang Province and Chinese Academy of Forestry(No.2017SY04)Key Discipline of Forestry of Creative Technology Project of Zhejiang Province(No.201511)Zhejiang Provincial Collaborative Innovation Center for Bamboo Resources and High-efficiency Utilization(No.S2017011)Startup Scientific Research Fund for Scholars of Zhejiang A&F University(No.2034020075)
文摘Bamboo forest is an important forest type in subtropical China and is characterized by fast growth and high carbon sequestration capacity. However, the dynamics of carbon fluxes during the fast growing period of bamboo shoots and their correlation with environment factors are poorly understood. We measured carbon dioxide exchange and climate variables using open-path eddy covariance methods during the 2011 growing season in a Moso bamboo forest(MB, Phyllostchys edulis) and a Lei bamboo forest(LB, Phyllostachys violascens) in Zhejiang province,China. The bamboo forests were carbon sinks during the growing season. The minimum diurnal net ecosystem exchange(NEE) at MB and LB sites were-0.64 and-0.66 mg C m^(-2) s^(-1), respectively. The minimum monthly NEE, ecosystem respiration(RE), and gross ecosystem exchange(GEE) were-99.3 ± 4.03, 76.2 ±2.46, and^(-1)91.5 ± 4.98 g C m^(-2) month^(-1), respectively,at MB site, compared with-31.8 ± 3.44, 70.4 ± 1.41,and^(-1)57.9 ± 4.86 g C m^(-2) month^(-1), respectively, at LB site. Maximum RE was 92.1 ± 1.32 g C m^(-2) month^(-1) at MB site and 151.0 ± 2.38 g C m^(-2) month^(-1) at LB site.Key control factors varied by month during the growing season, but across the whole growing season, NEE and GEE at both sites showed similar trends in sensitivities to photosynthetic active radiation and vapor pressure deficit,and air temperature had the strongest correlation with RE at both sites. Carbon fluxes at LB site were more sensitive to soil water content compared to those at MB site. Both onyear(years when many new shoots are produced) and offyear(years when none or few new shoots are produced)should be studied in bamboo forests to better understand their role in global carbon cycling.
基金funded by the National Natural Science Foundation of China (No. 41573064)the National Key Research and Development program of China (No. 2016YFA0601003)
文摘As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,reservoirs have important effects on the fluvial transport of material from land to ocean,and inevitably have complex terrain which can complicate and distort the results of seismic surveys.Therefore,there are still some problems need to be resolved in the application of seismic surveys in reservoirs with complex terrain.For this study,the Dongfeng Reservoir located in the upper reaches of the Wujiang River was chosen as an example to test the seismic survey method.Our testing showed that(1)because of the complex underwater terrain,the signal-to-noise ratio of the echo signal in canyon reservoir is low,making it difficult to determine sediment layers thicknesses in some areas;and(2)due to the large spatial heterogeneity of sediment distribution,insufficient density of cross-sections can lead to inaccurate interpolation results.To improve the accuracy of calculations,a mathematical method was used.Ultimately,the total burial mass of sediment was estimated at 2.85 x 107 tons,and the average burial rates of total organic carbon,total phosphorus,and total nitrogen were estimated at 0.194,0.011,and 0.014 g cm-2 year-1,respectively.These values were close to the results of previous studies and hydrographic station data,indicating that seismic survey can be a reliable and efficient method for the mapping of reservoirs.
基金financially supported by the National Natural Science Foundation of China (No. 51774024)
文摘To improve the heat transfer capability and the crystallization property of the traditional mold flux, CaF_2 was replaced with B_2O_3. Then, the influences of CeO_2 on the heat transfer and the crystallization of the CaF_2-bearing mold flux and the new mold flux with 10 wt% B_2O_3 were studied using a slag film heat flux simulator and X-ray diffraction(XRD). The results revealed that the addition of CeO2 reduced the heat transfer by increasing the solid slag thickness and the crystallization of two mold fluxes. However, CeO_2 had less effect on the B_2O_3-containing mold flux compared with the CaF_2-bearing mold flux. According to the analyses, the CeO_2 contents in the CaF_2-bearing mold flux and the B_2O_3-containing mold flux should not exceed 8 wt% and 12 wt%, respectively. Therefore, these experimental results are beneficial to improve and develop the mold flux for casting rare earth alloy steels.
基金supported financially by the Natural Science Foundation of Heilongjiang Province of China(LH2020C032)the Fundamental Research Funds for the Central Universities(No.2572018BA10)。
文摘Atmospheric deposition(dry and wet deposition)is one of the primary sources of chemical inputs to terrestrial ecosystems and replenishes the nutrient pool in forest ecosystems.Precipitation often acts as a primary transporting agent and solvent;thus,nutrient cycles in forests are closely linked to hydrological processes.We collected precipitation data during a growing season to explore variations in nutrient cycling and nutrient balances in the rainfall redistribution process(wet deposition)in a larch plantation in northeast China.We measured nutrient(NO_(3)^(-),PO_(4)^(3−),Cl^(−),K,Ca,Na,and Mg)inputs via bulk precipitation,throughfall and stemfl ow,and used a canopy budget model to estimate nutrient fl uxes via canopy exchange.Our results suggest that the average concentrations of the base cation(K,Ca,Na,and Mg)showed the following order:stemfl ow>throughfall>bulk precipitation.Throughfall and stemfl ow chemistry dramatically fl uctuated over the growing season when net fl uxes(throughfall+stemfl ow—bulk precipitation)of NO−3,PO3−4,SO2−4,Cl−,K,Ca,Na,and Mg were−6.676 kg·ha^(-1),−1.094 kg·ha^(-1),−2.371 kg·ha^(-1),1.975 kg·ha^(-1),0.470 kg·ha^(-1),−5.202 kg·ha^(-1),−0.336 kg·ha^(-1),and 1.397 kg·ha^(-1),respectively.These results suggest that NO−3,PO3−4,SO2−4,Ca,and Na were retained,while Cl−,K,and Mg were washed off by throughfall and stemfl ow.
文摘The biogeochemical behavior of DIN (dissolved inorganic nitrogen), phosphate and silicate in the Minjiang River estuary is discussed based on data obtained from May, 1990 to Feb., 1991 oceanographic surveys in the area. The annual fluxes of nutrients in the Minjiang River estuary were estimated to be 326.8 ×103 t for silicate, 771.0 t for phosphate, 45.7×103 t for DIN (42.1×103 t for nitrate, 3.0×103 t for ammonia. 600 t for nitrite), respectively.
基金supported by the National Science Foundation of China(Grant No.31971490).
文摘Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4)fluxes in wetlands.However,the symbiotic relationship between methanogens and methanotrophs remains unclear.To help close this research gap,we collected and analyzed samples from four soil depths in the Dajiuhu subalpine peatland in January,April,July,and October 2019 and acquired seasonal methane flux data from an eddy covariance(EC)system,and investigated relationships.A phylogenetic molecular ecological networks(pMENs)analysis was used to identify keystone species and the seasonal variations of the co-occurrence patterns of methanogenic and methanotrophic communities.The results indicate that the seasonal variations of the interactions between methanogenic and methanotrophic communities contributed to CH_(4)emissions in wetlands.The keystone species discerned by the network analysis also showed their importance in mediating CH_(4)fluxes.Methane(CH_(4))emissions in wetlands were lowest in spring;during this period,the most complex interactions between microbes were observed,with intense competition among methanogens while methanotrophs demonstrated better cooperation.Reverse patterns manifested themselves in summer when the highest CH_(4)flux was observed.Methanoregula formicica was negatively correlated with CH_(4)fluxes and occupied the largest ecological niches in the spring network.In contrast,both Methanocella arvoryzae and Methylocystaceae demonstrated positive correlations with CH_(4)fluxes and were better adapted to the microbial community in the summer.In addition,soil temperature and nitrogen were regarded as significant environmental factors to CH_(4)fluxes.This study was successful in explaining the seasonal patterns and microbial driving mechanisms of CH_(4)emissions in wetlands.
文摘The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO-2, NO-3, PO3-4 and SIO4-4) were measured in PW and BW in El Mex Bay and surround drains during spring 2010. Nutrient concentrations gradiance in PW with overlying seawater were evaluated according to Fick’s Law. Average inorganic nutrient fluxes were estimated using the pore water gradient concentration across the sediment-water interface. Calculated nutrient fluxes had averages of ﹣7.24, ﹣1.36, ﹣7.86 and ﹣1.33 in El Mex Bay. Additionally, the fluxes in the drains were ﹣34.39, ﹣32.28, ﹣53.20 and ﹣117.6 mg·m﹣2·day﹣1 for NO-3, NO-2, PO3-4 and SIO4-4, respectively. Mineralogical studies of sediment samples by using IR, X-ray analysis were carried out to identify the chemical structure of sediments. The results revealed that calcite, aragonite and quartz are the dominant minerals. On the other hand, differential thermal analysis (DTA) was used to evaluate and discuss different kinetic parameters such as Ea#, ΔG#, ΔH#, ΔS#, Z and Tm support the view of the extra stability of these sediments.
文摘<div style="text-align:justify;"> In this paper, we study the error estimates for direct discontinuous Galerkin methods based on the upwind-biased fluxes. We use a newly global projection to obtain the optimal error estimates. The numerical experiments imply that <em>L</em><sup>2 </sup>norms error estimates can reach to order <em>k</em> + 1 by using time discretization methods. </div>
文摘Wet deposition was collected in Mexico City (MC), Metropolitan Area of Monterrey (MAM) and El Chico National Park (ECNP), during 2009 and 2010. pH, conductivity, Cl-, , Na+, K+, Ca2+ and Mg2+ were determined. In MC, sulphate levels were greater than nitrate levels, and NH4 had mixed sources (vehicular emissions and agriculture activities). MAM had markedly alkaline atmospheric deposition, Na+ and Cl-levels were unexpectedly high, especially during hurricane “Alex”. Low pH values were found in ECNP and nitrate concentrations were high, suggesting the influence of a local source (forest fires). Deposition fluxes (Kg.ha-1yr-1) for N-NO3, N-NH4 and S-SO4 were 1.36, 2.74 and 4.84 for MAM;7.27, 0.57 and 4.32 for ECNP;and 5.97, 4.96 and 6.78 for MC, respectively. Nitrogen deposition fluxes in ECNP were high considering that this site is a natural reserve.
文摘Evapotranspiration acts an important role in hydrologic cycle and water resources planning. But the estimation issue still remains until nowadays. This research attempts to make clear this problem by the following way. In a humid region, by applying the Bowen ratio concept and optimum procedure on the soil surface, sensible and latent heat fluxes are estimated using net radiation (Rn) and heat flux into the ground (G). The method uses air temperature and humidity at a single height by reciprocally determining the soil surface temperature (Ts) and the relative humidity (rehs). This feature can be remarkably extended to the utilization. The validity of the method is confirmed by comparing of observed and estimated latent (lE) and sensible heat flux (H) using the eddy covariance method. The hourly change of the lE, H, Ts and rehs on the soil surface, yearly change of lE and H and relationship of estimated lE and H versus observed are clarified. Furthermore, monthly evapotranspiration is estimated from the lE. The research was conducted using hourly data of FLUXNET at a site of Japan, three sites of the United States and two sites of Europe in humid regions having over 1000 mm of annual precipitation.
文摘The surface exchange of NH<sub>3</sub> and HNO<sub>3</sub> gases over heathland was measured with theaerodynamic gradient method in Leende,the Netherlands during April 25 and May 9,1991.Due toreactions in the system NH<sub>3</sub>,HNO<sub>3</sub> and NH<sub>4</sub>NO<sub>3</sub>,the NH<sub>3</sub> deposition flux is overestimated,whileHNO<sub>3</sub> shows apparent emission fluxes mostly during the field experiment.Results reveal that NH<sub>3</sub>gradients are influenced slightly by HNO<sub>3</sub> and the HNO<sub>3</sub> gradients are strongly controlled by theNH<sub>3</sub>.A clear relationship between NH<sub>3</sub> and HNO<sub>3</sub> gradient is suggested by the Leende experiment.Before the late afternoon,NH<sub>3</sub> deposition gradients will cause HNO<sub>3</sub> upward gradients,meanwhilethe NH<sub>3</sub> gradients themselves will become smaller.After the HNO<sub>3</sub> upward gradient reaches maxi-mum,the NH<sub>3</sub> deposition gradients will be enlarged or the emission gradients depressed,while theHNO<sub>3</sub> upward gradients become smaller.
