Reformed solitary kinetic alfven waves due to dissipations and auroral electron acceleration

The physical nature of the auroral electron acceleration has been an outsta nding problem in space physics for decades. Some recent observations from t he auroral orbit satellites, FREJA and FAST, showed that large amplitude so litary kinetic Alfven waves (SKAWs) are a common electromagnetic active phe nomenon in the auroral magnetosphere. In a low-beta (i.e., beta /2 << m(e)/ m(i) << 1) plasma, the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions. Th is 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 dissi pation 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 m(e)v(A)(2)/e over a characteristic width of several lambda (e) . 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 r egion of 1-2 R-E above the auroral ionosphere, but also the accelerated ele ctrons from this region can obtain an energy of several keV and carry a fie ld-aligned current of several muA/m(2) which are comparable to the observat ions of auroral electrons.