Alfvén ship waves: high-<I>m</I> ULF pulsations in the magnetosphere generated by a moving plasma inhomogeneity

Abstract

Abstract. The generation of a high-m Alfvén wave by substorm injected energetic particles in the magnetosphere is studied. The wave is supposed to be emitted by an alternating current created by the drifting particle cloud or ring current inhomogeneity. It is shown that the wave appears in some azimuthal location simultaneously with the particle cloud arrival at the same spot. The value of the azimuthal wave number is determined as m∼ω/ω d , where ω is the eigenfrequency of the standing Alfvén wave and ω d is the particle drift frequency. The wave propagates westward, in the direction of the proton drift. Under the reasonable assumption about the density of the energetic particles, the amplitude of the generated wave is close to the observed amplitudes of poloidal ULF pulsations.

Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study

“…The data can be interpreted in terms of the theory of the wave generation by substorm injected particles as elaborated by Mager and Klimushkin (2008), Mager et al (2009) and Zolotukhina et al (2008), with, in this case an electron cloud of energy ∼33 keV acting as the wave source. According to the theory, wave comes into being with mixed polarization.…”

“…However, when these two modes have a different parallel structure (Leonovich, 2001) this coupling may under some circumstances be neglected and the excitation of the Alfvén waves can be studied alone. The theory of the generation of this mode by substorm injected particles has been elaborated by Mager and Klimushkin (2008) and Mager et al (2009). Although that theory was developed for the proton-driven high-m wave case, its qualitative features can be generalized for a more general situation, with lower m-numbers and a wave source in the energetic electron population (see Zolotukhina et al, 2008).…”

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

“…Aurora is characterized by a complicated spectrum of magnetic field oscillations, in particular in the ultra-low frequency (ULF) range, including Pi2 pulsations as an onset sensor (Olson, 1999) and pulsations both of Pi1/2 and Pc4-5 types specific to different stages of a substorm (Samson et al, 1992;Holter et al, 1995;Mager and Klimushkin, 2008). Presubstorm features in ULF parameters were studied by Saito et al (2008) and Liang et al (2009) but only concentrating on the final pre-onset minutes.…”

Generation of resonant Alfvén waves in the auroral oval

“…However, the assumption that substorm-related morning Pc5 pulsations are generated by resonant instabilities of energetic electrons, similar to the excitation of storm-time Pc5 waves in the dusk sector by energetic protons, contradicts ground-based observations, which show low m values and large lateral scales of these oscillations (Olson and Rostoker, 1978). A possibility for Alfvén wave generation by a non-steady transverse current of drifting energetic particles (the "ship waves" mechanism by Mager and Klimushkin, 2008) also results in the excitation of high-m waves. Rostoker and Lam (1978) proposed an interpretation of the electrojet-Pc5 relationship, suggesting that Pc5 waves are the eigenmodes of a 3-D magnetosphere-ionosphere current system.…”

“…(5) near the resonant point x R can be written in integral form, following Mager and Klimushkin (2008):…”