Beam-driven electron-acoustic waves in auroral region of magnetosphere with superthermal trapped electrons

The propagation characteristics of nonlinear electron-acoustic (EA) waves are studied in a four-component magneto-plasma, containing inertial cold electrons, warm drifting beam electrons, trapped superthermal hot electrons, and static ions. A linear dispersion relation for EA waves is derived to analyze the impact of electron superthermality on the ω−k relation. For nonlinear analysis, a reductive perturbation formalism is adopted to solve the set of model equations in the form of a trapped Zakharov–Kuznetsov (tZK) equation. The latter is analyzed to determine the solitary structures in terms of phase portraits and exact soliton solutions showing the impact of electron trapping efficiency (γ), hot electron superthermality (κ), drifting speed, temperature and density of beam electrons, and temperature and density of cold electrons, using typical parameters from the short-duration burst of broad-band electrostatic noise emissions observed by the Viking spacecraft in the auroral region. The solitary structures propagate as positive potential pulses and become modified with superthermal trapped electrons, leading to hole (hump) in cold (hot) electron density excitations. The electric field structures of the EA waves are found to be in exact agreement with the observed solitary structures in the auroral region. It is observed that electric field strength associated with these waves decreases as the magnetic field increases. The present model can be used to understand the transport of energy and momentum between plasma particles and to comprehend magnetic reconnection region in magnetopause, where two-temperature electrons and large-amplitude parallel electrostatic waves have been reported by magnetopause multiscale observations.