Oceanic geostrophic turbulence theory predicts significant inverse kinetic energy (KE) cascades at scales larger than the energy injection wavelength. However,the characteristics of the mesoscale variabilities associa...Oceanic geostrophic turbulence theory predicts significant inverse kinetic energy (KE) cascades at scales larger than the energy injection wavelength. However,the characteristics of the mesoscale variabilities associated with the inverse KE cascade in the real oceans have not been clear enough up to now. To further examine this problem,we analyzed the spectral characteristics of the oceanic mesoscale motions over the scales of inverse KE cascades based on high-resolution gridded altimeter data. The applicability of the quasigeostrophic (QG) turbulence theory and the surface quasigeostrophic (SQG) turbulence theory in real oceans is further explored. The results show that the sea surface height (SSH) spectral slope is linearly related to the eddy-kinetic-energy (EKE) level with a high correlation coefficient value of 0.67. The findings also suggest that the QG turbulence theory is an appropriate dynamic framework at the edge of high-EKE regions and that the SQG theory is more suitable in tropical regions and low-EKE regions at mid-high latitudes. New anisotropic characteristics of the inverse KE cascade are also provided. These results indicate that the along-track spectrum used by previous studies cannot reveal the dynamics of the mesoscale variabilities well.展开更多
A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue method.We show a special isotropic turbulence,in which the initial condi...A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue method.We show a special isotropic turbulence,in which the initial condition is constructed by reversing the velocity field in space,i.e.,the time-reversed turbulence.It is shown that the product of eigenvalues of the rate-of-strain tensor can quantitatively describe the backward energy transfer process.This description is consistent to the velocity derivative skewness Sk.However,compared with Sk,it is easier to be obtained,and it is expected to be extended to anisotropic turbulence.Furthermore,this description also works for the resolved velocity field,which means that it can be used in engineering turbulent flows.The description presented here is desired to inspire future investigation for the modeling of the backward energy transfer process and lay the foundation for the accurate prediction of complex flows.展开更多
The inverse cascade fl ux of kinetic energy(KE)and its length scale in the South Indian Countercurrent(SICC)region were investigated using 24-year satellite altimeter daily data from 1993–2016.The evolution of the ed...The inverse cascade fl ux of kinetic energy(KE)and its length scale in the South Indian Countercurrent(SICC)region were investigated using 24-year satellite altimeter daily data from 1993–2016.The evolution of the eddy life cycle in the SICC was presented systemically.It was found that the arrest and inject scales of inverse cascade were within the baroclinic most unstable scale and observed energy-containing eddy scale.The seasonal cycle of the arrest scale,inject scale,and amplitude of the inverse cascade were compared with the eddy kinetic energy seasonal cycle,which revealed a 1.5-month lag of the eddy kinetic energy to the vertical shear of zonal velocity,implying the existence of nonlinear processes during the eddy growth phase.Meanwhile,the anisotropy of the inverse cascade indicated that kinetic energy might be transferred from meridional motions to zonal motions,which is probably caused byβeff ect.These results would be benefi cial for a better understanding of the KE transfer processes in the SICC region.展开更多
A population inversion study of GaAs/AlxGa1-xAs three-quantum-well quantum cascade structures is presented. We derive the population inversion condition （PIC） of the active region （AR） and discuss the PICs on diff...A population inversion study of GaAs/AlxGa1-xAs three-quantum-well quantum cascade structures is presented. We derive the population inversion condition （PIC） of the active region （AR） and discuss the PICs on different structures by changing structural parameters such as the widths of quantum wells or barriers in the AR. For some instances, the PIC can be simplified and is proportional to the spontaneous emission lifetime between the second and the first excited states, whereas some other instances imply that the PIC is proportional to the state lifetime of the second excited state.展开更多
基金The National Key R&D Program of China under contract Nos 2016YFC0301203 and 2019YFC1407903the Natural Science Foundation of Hebei Province under contract No.D2019407046+1 种基金the Hebei Science and Technology Project under contract No.19273301Dthe NSFC-Shangdong Province Joint Fund under contract No.U1406401.
文摘Oceanic geostrophic turbulence theory predicts significant inverse kinetic energy (KE) cascades at scales larger than the energy injection wavelength. However,the characteristics of the mesoscale variabilities associated with the inverse KE cascade in the real oceans have not been clear enough up to now. To further examine this problem,we analyzed the spectral characteristics of the oceanic mesoscale motions over the scales of inverse KE cascades based on high-resolution gridded altimeter data. The applicability of the quasigeostrophic (QG) turbulence theory and the surface quasigeostrophic (SQG) turbulence theory in real oceans is further explored. The results show that the sea surface height (SSH) spectral slope is linearly related to the eddy-kinetic-energy (EKE) level with a high correlation coefficient value of 0.67. The findings also suggest that the QG turbulence theory is an appropriate dynamic framework at the edge of high-EKE regions and that the SQG theory is more suitable in tropical regions and low-EKE regions at mid-high latitudes. New anisotropic characteristics of the inverse KE cascade are also provided. These results indicate that the along-track spectrum used by previous studies cannot reveal the dynamics of the mesoscale variabilities well.
基金the National Natural Science Foundation of China(Nos.12002318 and51976203)the Central Government Guides Local Science and Technology Development Fund Projects(No.YDZX20191400002850)the Science Foundation of North University of China(No.XJJ201929)。
文摘A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue method.We show a special isotropic turbulence,in which the initial condition is constructed by reversing the velocity field in space,i.e.,the time-reversed turbulence.It is shown that the product of eigenvalues of the rate-of-strain tensor can quantitatively describe the backward energy transfer process.This description is consistent to the velocity derivative skewness Sk.However,compared with Sk,it is easier to be obtained,and it is expected to be extended to anisotropic turbulence.Furthermore,this description also works for the resolved velocity field,which means that it can be used in engineering turbulent flows.The description presented here is desired to inspire future investigation for the modeling of the backward energy transfer process and lay the foundation for the accurate prediction of complex flows.
基金Supported by the National Natural Science Foundation of China(Nos.41776035,41676007)the Funds for Creative Research Groups of China(No.41421005)。
文摘The inverse cascade fl ux of kinetic energy(KE)and its length scale in the South Indian Countercurrent(SICC)region were investigated using 24-year satellite altimeter daily data from 1993–2016.The evolution of the eddy life cycle in the SICC was presented systemically.It was found that the arrest and inject scales of inverse cascade were within the baroclinic most unstable scale and observed energy-containing eddy scale.The seasonal cycle of the arrest scale,inject scale,and amplitude of the inverse cascade were compared with the eddy kinetic energy seasonal cycle,which revealed a 1.5-month lag of the eddy kinetic energy to the vertical shear of zonal velocity,implying the existence of nonlinear processes during the eddy growth phase.Meanwhile,the anisotropy of the inverse cascade indicated that kinetic energy might be transferred from meridional motions to zonal motions,which is probably caused byβeff ect.These results would be benefi cial for a better understanding of the KE transfer processes in the SICC region.
基金supported by the National Natural Science Foundation of China(No.60976070)the Special Funds of China Academy of Engineering Physics(No.909)
文摘A population inversion study of GaAs/AlxGa1-xAs three-quantum-well quantum cascade structures is presented. We derive the population inversion condition （PIC） of the active region （AR） and discuss the PICs on different structures by changing structural parameters such as the widths of quantum wells or barriers in the AR. For some instances, the PIC can be simplified and is proportional to the spontaneous emission lifetime between the second and the first excited states, whereas some other instances imply that the PIC is proportional to the state lifetime of the second excited state.
