Reply to comment by F. Mottez on “Do magnetospheric shear Alfvén waves generate sufficient electron energy flux to power the aurora?”
نویسندگان
چکیده
[1] The gauge condition relating the electromagnetic potentials of shear Alfvén waves is one of the key governing equations in simulations of low-frequency waves in the Earth’s magnetosphere. Mottez [2013] suggests that the gauge condition used in Watt and Rankin [2010] is inappropriate for the case where the perpendicular wave number of the shear Alfvén wave varies as a function of distance along the field line. We present an alternate derivation of this gauge equation and argue that the assumptions used are appropriate for low-frequency shear Alfvén waves provided that the variation of the perpendicular wave number parallel to the geomagnetic field is much smaller than the corresponding variation of the field amplitude. [2] For a shear Alfvén wave in the magnetosphere, it is assumed that the perpendicular wavelengths are much smaller than the parallel wavelengths and that the frequency of the wave is much smaller than the local ion gyrofrequency. These assumptions allow us to represent the wave in terms of the scalar potential and the parallel component of the vector potential Ak only [Tikhonchuk and Rankin, 2000], delivering a considerable reduction in the spatial dimensions required for a numerical treatment. [3] The shear Alfvén wave is assumed to operate in a plasma which is quasi-neutral, hence r J = 0, where J is the current density. For low-frequency waves such as the shear Alfvén wave, this assumption is appropriate. If z is the direction along the field line and x is one of the directions perpendicular to the field, then we could also write @Jk @z + @J? @x = 0. (1)
منابع مشابه
Do magnetospheric shear Alfvén waves generate sufficient electron energy flux to power the aurora?
[1] Using a self‐consistent drift‐kinetic simulation code, we investigate whether electron acceleration owing to shear Alfvén waves in the plasma sheet boundary layer is sufficient to cause auroral brightening in the ionosphere. The free parameters used in the simulation code are guided by in situ observations of wave and plasma parameters in the magnetosphere at distances >4 RE from the Earth....
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