The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades,Some recent observations from the auroral orbit satellites,FREJA and FAST,showed that large amplitu...The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades,Some recent observations from the auroral orbit satellites,FREJA and FAST,showed that large amplitude solitary kinetic Alfven waves(SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere.In a low-β(i.e.,β/s<<me/mi<<1)plasma,the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions.This leads to instabilities and causes dissipations of SKAWs.In the present work,based on the analogy of classical particle motion in a potential well,it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included.The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of mevA^2/e over a characteristic width of several λe.As a consequence,the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local Alfven velocity.In particular,we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron acceleration problem.The result shows that not only the location of acceleration regions predicted by this model is well consistent with the observed auroral electron acceleration region of 1-2 RE above the auroral ionosphere,but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several μA/m^2 which are comparble to the observations of auroral electrons.展开更多
文摘The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades,Some recent observations from the auroral orbit satellites,FREJA and FAST,showed that large amplitude solitary kinetic Alfven waves(SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere.In a low-β(i.e.,β/s<<me/mi<<1)plasma,the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions.This leads to instabilities and causes dissipations of SKAWs.In the present work,based on the analogy of classical particle motion in a potential well,it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included.The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of mevA^2/e over a characteristic width of several λe.As a consequence,the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local Alfven velocity.In particular,we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron acceleration problem.The result shows that not only the location of acceleration regions predicted by this model is well consistent with the observed auroral electron acceleration region of 1-2 RE above the auroral ionosphere,but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several μA/m^2 which are comparble to the observations of auroral electrons.
