Computational studies of narrow electron beams and oblique inertial Alfven waves in a gravitationally bound density gradient

Two basic auroral processes are investigated using a novel 2.5D PIC code which supports the presence of a gravitationally-bound density gradient atmosphere. An electrostatic version of the code is used to investigate cold, narrow ($8.4lDe$) electron beams incident upon the gradient. Solitary structures are observed to form and interact strongly with the density gradient. Identified as electron phase space holes, they are observed to experience a gradient-ward (downward) acceleration force which compresses solitary structures as they move out of the gradient or rarefies them as they pass into the gradient. Complex mergers and other interactions are observed, including a fractal-like progression of streaming electrons causing phase space holes and vice versa. These structures appear to be similar to the “fast solitary waves” identified by the FAST satellite. An electromagnetic version of the code employs a restricted Darwin scheme to launch oblique, inertial Alfvén waves into a similar gradient. Strong wave reflection is noted as well as parallel wavelength modification. However, further analysis is hampered by insufficient computer memory. Necessary modifications of the simulation setup that would permit future successful Alfvén wave launching and gradient experiments are detailed.