THe effects of strong convection electric field on the electron density in the auroral ionosphericF-region have been simulated numerically by means of a physical model. It is found that an enhancement of electric fiel...THe effects of strong convection electric field on the electron density in the auroral ionosphericF-region have been simulated numerically by means of a physical model. It is found that an enhancement of electric field directed west-northward in post-noon or west-southward in pre-noon results in an ionization depletion with its maximum at altitudes 40–50 km higher than that of theF 2 peak. When the enhanced electric field lasts for 45 min and has a maximum about 32 mV/m, the resulted ionization depletions reach their maximum at the time just ～10 min behind the time when the convection electric field and ion temperature enhancements reach their maximum. This is consistent well with EISCAT observations. The magnitudes of the percentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal variation phase of the background electron density.展开更多
Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pr...Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMFB z component. Strong hard particle precipitation occurred in the initial phase for both storms, associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMFB z. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly inE-andF-region, but the electron temperature did quite different, with a strong increase in the lowerE-region relating to plasma instability excited by strong electric field and a slight decrease in theF-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.展开更多
The EISCAT data are used to confirm the important role of precipitation particles in the ionization rate in the auroral region. The height range of the effective ionization is quite different for particles with differ...The EISCAT data are used to confirm the important role of precipitation particles in the ionization rate in the auroral region. The height range of the effective ionization is quite different for particles with different energies. On the other hand, an enhancement of magnetospheric convection often results in decreasing of electron density, N , in the F layer. During January 28￣29,1985, the disturbed profiles of N were very typical, in which N m(E layer) N (F layer) and N decreased with height above 147 km. This phenomenan is caused by both energetic particles and intensive convection. During the period of February 16￣17, 1993, however, the N (F layer) increased extremely, while N (E layer) remained low. This is also a typical profile, but is opposite to the former one. In this case,the particles with lower energy (<1 keV) in the magnetosheath enter directly the high latitude ionosphere through the cusp,and can contribute significantly to the F layer ionization content.展开更多
基金the National Natural Science Foundation of China (496742 4140 0 740 3 9) and the Research Fund forthe Doctoral Program of Higher Education in China
文摘THe effects of strong convection electric field on the electron density in the auroral ionosphericF-region have been simulated numerically by means of a physical model. It is found that an enhancement of electric field directed west-northward in post-noon or west-southward in pre-noon results in an ionization depletion with its maximum at altitudes 40–50 km higher than that of theF 2 peak. When the enhanced electric field lasts for 45 min and has a maximum about 32 mV/m, the resulted ionization depletions reach their maximum at the time just ～10 min behind the time when the convection electric field and ion temperature enhancements reach their maximum. This is consistent well with EISCAT observations. The magnitudes of the percentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal variation phase of the background electron density.
基金Supported by the National Natural Science Foundation of China!(496 74241)the Research Fund for the DoctoralProgram of High
文摘Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMFB z component. Strong hard particle precipitation occurred in the initial phase for both storms, associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMFB z. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly inE-andF-region, but the electron temperature did quite different, with a strong increase in the lowerE-region relating to plasma instability excited by strong electric field and a slight decrease in theF-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.
文摘The EISCAT data are used to confirm the important role of precipitation particles in the ionization rate in the auroral region. The height range of the effective ionization is quite different for particles with different energies. On the other hand, an enhancement of magnetospheric convection often results in decreasing of electron density, N , in the F layer. During January 28￣29,1985, the disturbed profiles of N were very typical, in which N m(E layer) N (F layer) and N decreased with height above 147 km. This phenomenan is caused by both energetic particles and intensive convection. During the period of February 16￣17, 1993, however, the N (F layer) increased extremely, while N (E layer) remained low. This is also a typical profile, but is opposite to the former one. In this case,the particles with lower energy (<1 keV) in the magnetosheath enter directly the high latitude ionosphere through the cusp,and can contribute significantly to the F layer ionization content.
