Dispersion of low frequency plasma waves upstream of the quasi-perpendicular terrestrial bow shock

Abstract

Low frequency waves in the foot of a supercritical quasi-perpendicular shock front have been observed since the very early in situ observations of the terrestrial bow shock (Guha et al., 1972). The great attention that has been devoted to these type of waves since the first observations is explained by the key role attributed to them in the processes of energy redistribution in the shock front by various theoretical models. In some models, these waves play the role of the intermediator between the ions and electrons. It is assumed that they are generated by plasma instability that exist due to the counter-streaming flows of incident and reflected ions. In the second type of models, these waves result from the evolution of the shock front itself in the quasi-periodic process of steepening and overturning of the magnetic ramp. However, the range of the observed frequencies in the spacecraft frame are not enough to distinguish the origin of the observed waves. It also requires the determination of the wave vectors and the plasma frame frequencies. Multipoint measurements within the wave coherence length are needed for an ambiguous determination of the wave vectors. In the main multi-point missions such as ISEE, AMPTE, Cluster and THEMIS, the spacecraft separation is too large for such a wave vector determination and therefore only very few case studies are published (mainly for AMPTE UKS AMPTE IRM pair). Here we present the observations of upstream low frequency waves by the Cluster spacecraft which took place on 19 February 2002. The spacecraft separation during the crossing of the bow shock was small enough to determine the wave vectors and allowed the identification of the plasma wave dispersion relation for the observed waves. Presented results are compared with whistler wave dispersion and it is shown that contrary to previous studies based on the AMPTE data, the phase velocity in the shock frame is directed downstream. The consequences of this finding for both types of models that were developed to explain the generation of these waves are discussed

The Response of the Venusian Plasma Environment to the Passage of an ICME: Hybrid Simulation Results and Venus Express Observations

“…There are a number of candidates for these waves such as whistler waves (Russell, ), ion cyclotron waves (Delva et al, ; Wei et al, ), and nonlinear magnetic structures (Walker et al, ). It is our interpretation that the waves upstream are Doppler‐shifted whistler mode waves as similar dispersive wave trains are commonly observed upstream of planetary bow shocks (Dimmock et al, ) with comparable characteristics. We also suggest that the downstream waves are also likely whistler waves transmitted from upstream.…”

A statistical study of magnetic field fluctuations in the dayside magnetosheath and their dependence on upstream solar wind conditions

“…Magnetic field turbulence in the MS is often associated with electromagnetic waves such as whistler, mirror mode, and kinetic Alfvén waves which are known to occupy the MS. Preferably, the physical process corresponding to the observations would be determined but spatial‐temporal ambiguities make such investigations difficult especially on a statistical basis. This issue can be resolved using several techniques typically relying on theoretical models or techniques which are dependent on multispacecraft measurements [see Hoppe et al , ; Dimmock et al , ]. However, theoretical models can often be very specific which in turn provide limited applicability.…”

Two-stream instabilities from the lower-hybrid frequency to the electron cyclotron frequency: application to the front of quasi-perpendicular shocks

“…Whistler waves especially in the lower-hybrid range have interested theorists and simulationists owing to their potential role for transferring energy between ions and electrons (e.g., Wu et al, 1983;Winske et al, 1985;Scholer, 2003, 2006). Observationally, an important characteristic of whistlers in this regime is that the waves appear to propagate obliquely with respect to B o (Krasnoselskikh et al, 1991;Hull et al, 2012;Sundkvist et al, 2012;Dimmock et al, 2013). Moreover, when the waves can be put into their macroscopic context, their wavevectors have been measured as equally oblique with respect to the shock normal (Hull et al, 2012;Dimmock et al, 2013).…”

“…Observationally, an important characteristic of whistlers in this regime is that the waves appear to propagate obliquely with respect to B o (Krasnoselskikh et al, 1991;Hull et al, 2012;Sundkvist et al, 2012;Dimmock et al, 2013). Moreover, when the waves can be put into their macroscopic context, their wavevectors have been measured as equally oblique with respect to the shock normal (Hull et al, 2012;Dimmock et al, 2013). Since the normal presumably corresponds to the direction of the drift between the ion populations, the waves appear to propagate at a sizable angle with respect to the drift.…”