ULF waves excited by negative/positive solar wind dynamic pressure impulses at geosynchronous orbit

Abstract

1] When a solar wind dynamic pressure impulse impinges on the magnetophere, ultralow-frequency (ULF) waves can be excited in the magnetosphere and the solar wind energy can be transported from interplanetary space into the inner magnetosphere. In this paper, we have systematically studied ULF waves excited at geosynchronous orbit by both positive and negative solar wind dynamic pressure pulses. We have identified 270 ULF events excited by positive solar wind dynamic pressure pulses and 254 ULF events excited by negative pulses from 1 January 2001 to 31 March 2009. We have found that the poloidal and toroidal waves excited by positive and negative pressure pulses oscillate in a similar manner of phase near 06:00 local time (LT) and 18:00 LT, but in antiphase near 12:00 LT and 0:00 LT. Furthermore, it is shown that excited ULF oscillations are in general stronger around local noon than those in the dawn and dusk flanks. It is demonstrated that disturbances induced by negative impulses are weaker than those by positive ones, and the poloidal wave amplitudes are stronger than the toroidal wave amplitudes both in positive and negative events. The potential impact of these excited waves on energetic electrons at geosynchronous orbit has also been discussed.

Fast acceleration of “killer” electrons and energetic ions by interplanetary shock stimulated ULF waves in the inner magnetosphere

“…The variations of magnetic field, B r , and electric field, E ϕ , for poloidal waves are the result of numerical simulation. The blue solid line and red dashed line represent the poloidal ULF waves excited by positive and negative impulse respectively [49]. As shown in Figure 3, the amplitude of the poloidal wave is larger at 11 LT than it is that at 0 LT and 06 LT.…”

“…The wave that is excited by positive and negative impulse is similar in amplitude and 180° out of phase. These results have been further proved by statistical analysis of GOES magnetic field data at geosynchronous orbit [49].…”

“…The solar wind dynamic pressure pulses will compress the magnetopause first and then launch the fast magnetosonic wave inside the magnetosphere. This wave could further stimulate FLR in the dayside magnetosphere around the magnetic local noon [49].…”

“…The sudden raise/drop of solar wind dynamic pressure will cause compression/inflation of the magnetosphere [49], which further excites ULF waves in the magnetosphere [28,49].…”

Van Allen Probe observations of drift-bounce resonances with Pc 4 pulsations and wave–particle interactions in the pre-midnight inner magnetosphere

“…Toroidal pulsations have been attributed to a wide variety of mechanisms, including field line resonances triggered by abrupt changes and sudden impulses in the solar wind dynamic pressure (e.g., Zhang et al, 2010;Sarris et al, 2010), the Kelvin-Helmholtz instability (KHI) at the magnetopause (e.g., Pu and Kivelson, 1983;Fujita et al, 1996), and bursty reconnection and the generation of flux transfer events on the magnetopause (Gillis et al, 1987). Poloidal pulsations have also been attributed to a number of mechanisms, most notably drift-bounce resonances, ballooning modes, and drift mirror mode instabilities (Hasegawa, 1969;Lanzerotti et al, 1969;Hughes et al, 1979;Engebretson et al, 1992;Korotova et al, 2009;Liu et al, 2013).…”