On the origin of fluctuations in the cusp diamagnetic cavity

Abstract

[1] We have analyzed Cluster magnetic field and plasma data during high-altitude cusp crossing on 14 February 2003. Cluster encountered a diamagnetic cavity (DMC) during northward interplanetary magnetic field (IMF) conditions, and as IMF rotated southward, the spacecraft reencountered the cavity more at the sunward side. The DMC is characterized by a high level of magnetic field fluctuations and high-energy electrons and protons. Ultralow-frequency turbulence has been suggested as a mechanism to accelerate particles in DMC. We demonstrate in this paper for the first time that many of the low-frequency fluctuations in the cavity are back and forth motion of the DMC boundaries over the spacecraft and transient reconnection signatures. We also find examples of some isolated high-amplitude waves that could possibly be nonlinear kinetic magnetosonic modes. The lack of strong wave power at the vicinity of local ion cyclotron frequency in the DMC suggests that perhaps a mechanism other than wave-particle heating is a dominant source for ion heating in DMCs.

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

“…Though some observations agree with this gradual character for the inner transitions, for example Niehof et al (2010); Nykyri et al (2011a), others describe a much more rapid transition (Lavraud et al, 2002). This may be partly due to the dynamic nature of the cusp region, for instance Nykyri et al (2011b) have shown that some of the local fluctuations in plasma parameters within the CDC may be attributed to the reaction of the CDC to solar wind changes on relatively short timescales. This gradual transition in the simulation may also be caused by limited resolution (note that the simulation already has a much higher resolution than typical global models) or by physics not contained within our model such as dipole tilt or inherent fluctuations within the solar wind plasma.…”

Properties of a large-scale flux rope and current sheet region on the dayside of Mars: MGS MAG/ER and MEX ASPERA-3 ELS observations

“…Similar structures of depressed magnetic field are also observed in the high-altitude cusps regions of the Earth, as associated with the observations of cusp energetic particles and ULF wave activity (Nykyri et al, 2011). Therefore, if involving open crustal magnetic field, the observation of an extended current sheet and hot diamagnetic region at Mars could represent an analogy to the cusp diamagnetic cavities of the Earth.…”

“…Lower frequency fluctuations of approximately 0.003 Hz (330 s) were found embedded within the magnetic field vectors showing the current sheet rotation (B x and B y component), indicating either temporal changes from the movement of the current sheet position over the spacecraft, or spatial changes as the spacecraft crossed different sides of the current sheet. Nykyri et al (2011) proposed that a similar property observed in diamagnetic cavities at the cusp regions of the Earth's magnetosphere as responsible for accelerating particles.…”

Comparison Between Fluid Simulation With Test Particles and Hybrid Simulation for the Kelvin‐Helmholtz Instability

“…The test particle simulation agrees well with the hybrid simulation at the early nonlinear stage; however, there is large deviation in the vortex region at the later nonlinear stage. This anisotropic temperature is likely to driven small-scale kinetic waves (e.g., mirror modes and ion cyclotron waves; Dimmock et al, 2015;Dimmock et al, 2017;Nykyri et al, 2003;Nykyri et al, 2011) and secondary instabilities (e.g., firehose instability). Note in Figure 4, these two simulations have similar 3 ∕ 1 value in the vortex region, meaning this deviation may be attributed to the different magnetic field directions in fluid and hybrid simulations.…”