A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the ...A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the impact of the spin-up forcing in the initialization stage on the fractional coverages （FCs） of plant functional type （PFT） in the subsequent simulation stage are assessed in seven classic climate regions by a modified Community Land Model’s Dynamic Global Vegetation Model （CLM-DGVM）. Results show that the impact of spin-up forcing is considerable in all regions except the tropical rainforest climate region （TR） and the wet temperate climate region （WM）. In the tropical monsoon climate region （TM）, the TR and TM transition region （TR-TM）, the dry temperate climate region （DM）, the highland climate region （H）, and the boreal forest climate region （BF）, where FCs are affected by climate non-negligibly, the discrepancies in initial FCs, which represent long-term cumulative response of vegetation to different climate anomalies, are large. Moreover, the large discrepancies in initial FCs usually decay slowly because there are trees or shrubs in the five regions. The intrinsic growth timescales of FCs for tree PFTs and shrub PFTs are long, and the variation of FCs of tree PFTs or shrub PFTs can affect that of grass PFTs.展开更多
This paper mainly studies the electrical current control of the spinning bare electrodynamic tether system(SBEDT)during its spin-up process.The SBEDT combines the high electrical absorption efficiency of bare tethers ...This paper mainly studies the electrical current control of the spinning bare electrodynamic tether system(SBEDT)during its spin-up process.The SBEDT combines the high electrical absorption efficiency of bare tethers and the centrifugal stability of spinning tethers,which provides a propellant-free solution to missions including space debris removal,artificial gravity,and payload transportation.However,the nonlinear current distribution of bare tethers poses serious challenges to its dynamic and control.To deal with this problem,this paper focuses on the current analysis and optimal control of tether motions.First,a dynamic model is established for analyzing the varying currents in different positions,and the analytical expressions of the electrodynamic force are given.Second,the minimum tether length for spin-up is calculated by the maximum equilibrium position,providing a theoretical basis for system design.Third,an optimal tether deploying/retrieving controller is proposed to adjust electrodynamic force.The control law is designed according to the Bellman optimality principle,which tracks the angular velocity and controls the tether length within a certain range.Under the proposed analyzing method and the corresponding control strategy,spinning stability can be maintained during the spin-up process and the system successfully reaches the desired spinning state.展开更多
The spin-up time TA in the spin-up process and spin-down time TD in the spin-down process of rotational air flow in the cylindrical vortex chamber with three kinds of the artificial surface roughness were investigated...The spin-up time TA in the spin-up process and spin-down time TD in the spin-down process of rotational air flow in the cylindrical vortex chamber with three kinds of the artificial surface roughness were investigated. One of the most different characteristics between the smooth and rough surface conditions was the spin-down time TD. Also the transient response of the tangential velocity on the spin-up process was analyzed numerically and this result was compared with the experimental results. The above stated results are reported here in detail.展开更多
In this paper, the numerical experiments on the issue of spin-up time for seasonal-scale regional climate modeling were conducted with the newly Regional Climate Model （RegCM3）, in the case of the abnormal climate e...In this paper, the numerical experiments on the issue of spin-up time for seasonal-scale regional climate modeling were conducted with the newly Regional Climate Model （RegCM3）, in the case of the abnormal climate event during the summer of 1998 in China. To test the effect of spin-up time on the regional climate simulation results for such abnormal climate event, a total of 11 experiments were performed with different spin-up time from 10 days to 6 months, respectively. The simulation results show that, for the meteorological variables in the atmosphere, the model would be running in “climate mode” after 4-8-day spin-up time, then, it is independent of the spin-up time basically, and the simulation errors are mainly caused by the model＇ s failure in describing the atmospheric processes over the model domain. This verifies again that the regional climate modeling is indeed a lateral boundary condition problem as demonstrated by earlier research work. The simulated mean precipitation rate over each subregion is not sensitive to the spin-up time, but the precipitation scenario is somewhat different for the experiment with different spin-up time, which shows that there exists the uncertainty in the simulation to precipitation scenario, and such a uncertainty exhibits more over the areas where heavy rainfall happened. Generally, for monthly-scale precipitation simulation, a soin-uo time of 1 month is enough, whereas a spin-up time of 2 months is better for seasonal-scale one. Furthermore, the relationship between the precipitation simulation error and the advancement/withdrawal of East Asian summer monsoon was analyzed. It is found that the variability of correlation coefficient for precipitation is more significant over the areas where the summer monsoon is predominant. Therefore, the model＇s capability in reproducing precipitation features is related to the heavy rainfall processes associated with the advancement/withdrawal of East Asian summer monsoon, which suggests that it is necessary to develop a more reliable parameterization scheme to capture the convective precipitation of heavy rainfall pro- cesses associated with the activities of East Asian summer monsoon, so as to improve the climate modeling over China.展开更多
A modified three-dimensional turbulence parameterization scheme,implemented by replacing the conventional eddydiffusivity formulation with the H-gradient model,has shown good performance in representing the subgrid-sc...A modified three-dimensional turbulence parameterization scheme,implemented by replacing the conventional eddydiffusivity formulation with the H-gradient model,has shown good performance in representing the subgrid-scale(SGS)turbulent fluxes associated with convective clouds in idealized tropical cyclone(TC)simulations.To evaluate the capability of the modified scheme in simulating real TCs,two sets of simulations of TC Soudelor(2015),one with the modified scheme and the other with the original scheme,are conducted.Comparisons with observations and coarse-grained results from large eddy simulation benchmarks demonstrate that the modified scheme improves the forecasting of the intensity and structure,as well as the SGS turbulent fluxes of Soudelor.Using the modified turbulence scheme,a TC with stronger intensity,smaller size,a shallower but stronger inflow layer,and a more intense but less inclined convective updraft is simulated.The rapid intensification process and secondary eyewall features can also be captured better by the modified scheme.By analyzing the mechanism by which turbulent transport impacts the intensity and structure of TCs,it is shown that accurately representing the turbulent transport associated with convective clouds above the planetary boundary layer helps to initiate the TC spin-up process.展开更多
基于TRAMS(Tropical Regional Atmospheric Model System)区域模式和ECMWF(European Centre for Medium-range Weather Forecasting)全球分析场资料,对一次华南暖区暴雨过程进行IAU-Replay模拟试验。由于本次个例模拟试验的分析时刻ECMW...基于TRAMS(Tropical Regional Atmospheric Model System)区域模式和ECMWF(European Centre for Medium-range Weather Forecasting)全球分析场资料,对一次华南暖区暴雨过程进行IAU-Replay模拟试验。由于本次个例模拟试验的分析时刻ECMWF分析场和TRAMS模式正好处于比较协调的状态,直接使用全球分析场进行冷启动也不会激发虚假高频短波,因此IAU-Replay方法对于模拟结果的初始平衡性影响较小。从动力场和水物质场的对比可以发现,IAU-Replay方法通过提前启动模式有效避免了Spin-up过程的影响,这对于降水预报具有明显的改进效果。对IAU-Replay中不同预热时间的敏感性进行测试,发现当预热时间从6 h延长至12 h后模式可以更加合理地模拟出与对流系统中直接相关的中小尺度信息,从而使降水预报效果更接近实况。连续一周的预报结果评估进一步验证了IAU-Replay技术的有效性。展开更多
Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subt...Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subtle differences in initializations of(a)500-850-h Pa environmental winds,and(b)midlevel moisture and ventilation.We then describe how these differences impact on the evolving convective organization,storm structure,and the timing of RI.As expected,ascent,diabatic heating and the secondary circulation near the inner-core are much stronger in the member that best forecasts the RI.The evolution of vortex cloudiness from this member is similar to the actual imagery,with the development of an inner cloud band wrapping inwards to form the eyewall.We present evidence that this structure,and hence the enhanced diabatic heating,is related to the tilt and associated dynamics of the developing inner-core in shear.For the most accurate ensemble member:(a)inhibition of ascent and a reduction in convection over the up-shear sector allow moistening of the boundary-layer air,which is transported to the down-shear sector to feed a developing convective asymmetry;(b)with minimal ventilation,undiluted clouds and moisture from the down-shear left quadrant are then wrapped inwards to the up-shear left quadrant to form the eyewall cloud;and(c)this process seems related to a critical down-shear tilt of the vortex from midlevels,and the vertical phase-locking of the circulation over up-shear quadrants.For the member that forecasts a much-delayed RI,these processes are inhibited by stronger vertical wind shear,initially resulting in poor vertical coherence of the circulation,lesser moisture and larger ventilation.Our analysis suggests that ensemble prediction is needed to account for the sensitivity of forecasts to a relatively narrow range of environmental wind shear,moisture and vortex inner-structure.展开更多
基金supported by the Chinese Academy of Sciences under Grant No.KZCX2-YW-219State Key Project for Basic Research Program of China(973)under Grant No.2010CB951801Key Program of National Natural Science Foundation under Grant No.40830103
文摘A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the impact of the spin-up forcing in the initialization stage on the fractional coverages （FCs） of plant functional type （PFT） in the subsequent simulation stage are assessed in seven classic climate regions by a modified Community Land Model’s Dynamic Global Vegetation Model （CLM-DGVM）. Results show that the impact of spin-up forcing is considerable in all regions except the tropical rainforest climate region （TR） and the wet temperate climate region （WM）. In the tropical monsoon climate region （TM）, the TR and TM transition region （TR-TM）, the dry temperate climate region （DM）, the highland climate region （H）, and the boreal forest climate region （BF）, where FCs are affected by climate non-negligibly, the discrepancies in initial FCs, which represent long-term cumulative response of vegetation to different climate anomalies, are large. Moreover, the large discrepancies in initial FCs usually decay slowly because there are trees or shrubs in the five regions. The intrinsic growth timescales of FCs for tree PFTs and shrub PFTs are long, and the variation of FCs of tree PFTs or shrub PFTs can affect that of grass PFTs.
基金support of the Natural Science Foundation of ChongqingChina(No.2023NSCQ-MSX2403)+2 种基金the Natural Science Basic Research Program of Shaanxi(No.2024JC-YBQN-0650)the China Postdoctoral Science Foundation(No.2023M732862)funded by the Chinese Scholarship Council
文摘This paper mainly studies the electrical current control of the spinning bare electrodynamic tether system(SBEDT)during its spin-up process.The SBEDT combines the high electrical absorption efficiency of bare tethers and the centrifugal stability of spinning tethers,which provides a propellant-free solution to missions including space debris removal,artificial gravity,and payload transportation.However,the nonlinear current distribution of bare tethers poses serious challenges to its dynamic and control.To deal with this problem,this paper focuses on the current analysis and optimal control of tether motions.First,a dynamic model is established for analyzing the varying currents in different positions,and the analytical expressions of the electrodynamic force are given.Second,the minimum tether length for spin-up is calculated by the maximum equilibrium position,providing a theoretical basis for system design.Third,an optimal tether deploying/retrieving controller is proposed to adjust electrodynamic force.The control law is designed according to the Bellman optimality principle,which tracks the angular velocity and controls the tether length within a certain range.Under the proposed analyzing method and the corresponding control strategy,spinning stability can be maintained during the spin-up process and the system successfully reaches the desired spinning state.
文摘The spin-up time TA in the spin-up process and spin-down time TD in the spin-down process of rotational air flow in the cylindrical vortex chamber with three kinds of the artificial surface roughness were investigated. One of the most different characteristics between the smooth and rough surface conditions was the spin-down time TD. Also the transient response of the tangential velocity on the spin-up process was analyzed numerically and this result was compared with the experimental results. The above stated results are reported here in detail.
基金Supported jointly by the National Natural Science Foundation of China under Grant Nos.40675065,40333026the Program of Jiangsu Key Laboratory of Meteorological Disaster (KJS0605).
文摘In this paper, the numerical experiments on the issue of spin-up time for seasonal-scale regional climate modeling were conducted with the newly Regional Climate Model （RegCM3）, in the case of the abnormal climate event during the summer of 1998 in China. To test the effect of spin-up time on the regional climate simulation results for such abnormal climate event, a total of 11 experiments were performed with different spin-up time from 10 days to 6 months, respectively. The simulation results show that, for the meteorological variables in the atmosphere, the model would be running in “climate mode” after 4-8-day spin-up time, then, it is independent of the spin-up time basically, and the simulation errors are mainly caused by the model＇ s failure in describing the atmospheric processes over the model domain. This verifies again that the regional climate modeling is indeed a lateral boundary condition problem as demonstrated by earlier research work. The simulated mean precipitation rate over each subregion is not sensitive to the spin-up time, but the precipitation scenario is somewhat different for the experiment with different spin-up time, which shows that there exists the uncertainty in the simulation to precipitation scenario, and such a uncertainty exhibits more over the areas where heavy rainfall happened. Generally, for monthly-scale precipitation simulation, a soin-uo time of 1 month is enough, whereas a spin-up time of 2 months is better for seasonal-scale one. Furthermore, the relationship between the precipitation simulation error and the advancement/withdrawal of East Asian summer monsoon was analyzed. It is found that the variability of correlation coefficient for precipitation is more significant over the areas where the summer monsoon is predominant. Therefore, the model＇s capability in reproducing precipitation features is related to the heavy rainfall processes associated with the advancement/withdrawal of East Asian summer monsoon, which suggests that it is necessary to develop a more reliable parameterization scheme to capture the convective precipitation of heavy rainfall pro- cesses associated with the activities of East Asian summer monsoon, so as to improve the climate modeling over China.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFC3000803)the National Natural Science Foundation of China(Grant Nos.42375149,41975133 and 42205070)the Shanghai Pujiang Program(Grant No.22PJ1415900)。
文摘A modified three-dimensional turbulence parameterization scheme,implemented by replacing the conventional eddydiffusivity formulation with the H-gradient model,has shown good performance in representing the subgrid-scale(SGS)turbulent fluxes associated with convective clouds in idealized tropical cyclone(TC)simulations.To evaluate the capability of the modified scheme in simulating real TCs,two sets of simulations of TC Soudelor(2015),one with the modified scheme and the other with the original scheme,are conducted.Comparisons with observations and coarse-grained results from large eddy simulation benchmarks demonstrate that the modified scheme improves the forecasting of the intensity and structure,as well as the SGS turbulent fluxes of Soudelor.Using the modified turbulence scheme,a TC with stronger intensity,smaller size,a shallower but stronger inflow layer,and a more intense but less inclined convective updraft is simulated.The rapid intensification process and secondary eyewall features can also be captured better by the modified scheme.By analyzing the mechanism by which turbulent transport impacts the intensity and structure of TCs,it is shown that accurately representing the turbulent transport associated with convective clouds above the planetary boundary layer helps to initiate the TC spin-up process.
文摘基于TRAMS(Tropical Regional Atmospheric Model System)区域模式和ECMWF(European Centre for Medium-range Weather Forecasting)全球分析场资料,对一次华南暖区暴雨过程进行IAU-Replay模拟试验。由于本次个例模拟试验的分析时刻ECMWF分析场和TRAMS模式正好处于比较协调的状态,直接使用全球分析场进行冷启动也不会激发虚假高频短波,因此IAU-Replay方法对于模拟结果的初始平衡性影响较小。从动力场和水物质场的对比可以发现,IAU-Replay方法通过提前启动模式有效避免了Spin-up过程的影响,这对于降水预报具有明显的改进效果。对IAU-Replay中不同预热时间的敏感性进行测试,发现当预热时间从6 h延长至12 h后模式可以更加合理地模拟出与对流系统中直接相关的中小尺度信息,从而使降水预报效果更接近实况。连续一周的预报结果评估进一步验证了IAU-Replay技术的有效性。
基金partially supported by the National Natural Science Foundation of China (Grant Nos. 41365005, 41765007 and 41705038)the Hainan Key Cooperation Program (Grant No. ZDYF2019213)the Natural Science Foundation of Hainan Province of China (Grant No. 417298)
文摘Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subtle differences in initializations of(a)500-850-h Pa environmental winds,and(b)midlevel moisture and ventilation.We then describe how these differences impact on the evolving convective organization,storm structure,and the timing of RI.As expected,ascent,diabatic heating and the secondary circulation near the inner-core are much stronger in the member that best forecasts the RI.The evolution of vortex cloudiness from this member is similar to the actual imagery,with the development of an inner cloud band wrapping inwards to form the eyewall.We present evidence that this structure,and hence the enhanced diabatic heating,is related to the tilt and associated dynamics of the developing inner-core in shear.For the most accurate ensemble member:(a)inhibition of ascent and a reduction in convection over the up-shear sector allow moistening of the boundary-layer air,which is transported to the down-shear sector to feed a developing convective asymmetry;(b)with minimal ventilation,undiluted clouds and moisture from the down-shear left quadrant are then wrapped inwards to the up-shear left quadrant to form the eyewall cloud;and(c)this process seems related to a critical down-shear tilt of the vortex from midlevels,and the vertical phase-locking of the circulation over up-shear quadrants.For the member that forecasts a much-delayed RI,these processes are inhibited by stronger vertical wind shear,initially resulting in poor vertical coherence of the circulation,lesser moisture and larger ventilation.Our analysis suggests that ensemble prediction is needed to account for the sensitivity of forecasts to a relatively narrow range of environmental wind shear,moisture and vortex inner-structure.
