Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary mo...Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions.展开更多
A new strategy is presented to explain the creation and persistence of zonal flows widely observed in plasma edge turbulence.The core physics in the edge regime of the magnetic-fusion tokamaks can be described qualita...A new strategy is presented to explain the creation and persistence of zonal flows widely observed in plasma edge turbulence.The core physics in the edge regime of the magnetic-fusion tokamaks can be described qualitatively by the one-state modified Hasegawa-Mima(MHM for short)model,which creates enhanced zonal flows and more physically relevant features in comparison with the familiar Charney-Hasegawa-Mima(CHM for short)model for both plasma and geophysical flows.The generation mechanism of zonal jets is displayed from the secondary instability analysis via nonlinear interactions with a background base state.Strong exponential growth in the zonal modes is induced due to a non-zonal drift wave base state in the MHM model,while stabilizing damping effect is shown with a zonal flow base state.Together with the selective decay effect from the dissipation,the secondary instability offers a complete characterization of the convergence process to the purely zonal structure.Direct numerical simulations with and without dissipation are carried out to confirm the instability theory.It shows clearly the emergence of a dominant zonal flow from pure non-zonal drift waves with small perturbation in the initial configuration.In comparison,the CHM model does not create instability in the zonal modes and usually converges to homogeneous turbulence.展开更多
Equatorial spread-F (ESF) backscatter plumes are often observed in radar range-time-intensity (RTI) maps at low latitude. Except case studies, few statistical investigations on the onset locations of scintillation-pro...Equatorial spread-F (ESF) backscatter plumes are often observed in radar range-time-intensity (RTI) maps at low latitude. Except case studies, few statistical investigations on the onset locations of scintillation-producing ESF plumes at given sites have been conducted. In this study, a statistical analysis is carried out on onset locations of ESF backscatter plumes observed at a low-latitude location Sanya (18.4°N, 109.6°E; dip lat 12.8°N) during equinoctial months of 2013. By employing a tracing method to locate backscatter plumes, we estimate the onset longitudes of periodic plumes obtained from the Sanya VHF radar five-beam steering measurements. The results show that the inter-plume distances (in longitude) are mostly confined within 200–600 km, and the ESF plumes producing ionospheric scintillations over Sanya are almost exclusively generated at the longitudes of 94°–110°E. The results indicate the necessity to monitor ESF plume initial generation in the longitude region of 94°–110°E to better understand the day-to-day variability in the occurrence of ionospheric scintillations over Sanya.展开更多
基金supported by National Natural Science Foundation of China (No. 10775137)by the Ministry of Science and Technology of China (No. 2009CB105001)partly by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion
文摘Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions.
基金supported by the Office of Naval Research through MURI(No.N00014-16-1-2161)
文摘A new strategy is presented to explain the creation and persistence of zonal flows widely observed in plasma edge turbulence.The core physics in the edge regime of the magnetic-fusion tokamaks can be described qualitatively by the one-state modified Hasegawa-Mima(MHM for short)model,which creates enhanced zonal flows and more physically relevant features in comparison with the familiar Charney-Hasegawa-Mima(CHM for short)model for both plasma and geophysical flows.The generation mechanism of zonal jets is displayed from the secondary instability analysis via nonlinear interactions with a background base state.Strong exponential growth in the zonal modes is induced due to a non-zonal drift wave base state in the MHM model,while stabilizing damping effect is shown with a zonal flow base state.Together with the selective decay effect from the dissipation,the secondary instability offers a complete characterization of the convergence process to the purely zonal structure.Direct numerical simulations with and without dissipation are carried out to confirm the instability theory.It shows clearly the emergence of a dominant zonal flow from pure non-zonal drift waves with small perturbation in the initial configuration.In comparison,the CHM model does not create instability in the zonal modes and usually converges to homogeneous turbulence.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41422404, 41374163,41374164 and 41074113)
文摘Equatorial spread-F (ESF) backscatter plumes are often observed in radar range-time-intensity (RTI) maps at low latitude. Except case studies, few statistical investigations on the onset locations of scintillation-producing ESF plumes at given sites have been conducted. In this study, a statistical analysis is carried out on onset locations of ESF backscatter plumes observed at a low-latitude location Sanya (18.4°N, 109.6°E; dip lat 12.8°N) during equinoctial months of 2013. By employing a tracing method to locate backscatter plumes, we estimate the onset longitudes of periodic plumes obtained from the Sanya VHF radar five-beam steering measurements. The results show that the inter-plume distances (in longitude) are mostly confined within 200–600 km, and the ESF plumes producing ionospheric scintillations over Sanya are almost exclusively generated at the longitudes of 94°–110°E. The results indicate the necessity to monitor ESF plume initial generation in the longitude region of 94°–110°E to better understand the day-to-day variability in the occurrence of ionospheric scintillations over Sanya.
