-
[show abstract]
[hide abstract]
ABSTRACT: We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfvén waves with ω(plas) ≤ 0.1ω(ci) down to k(⊥) ρ(i)∼2. Each k spectrum in the direction perpendicular to B0 shows two scaling ranges separated by a breakpoint (in the interval [0.4,1]k(⊥)ρ(i): a Kolmogorov scaling k(⊥)⁻¹ⁱ⁷ followed by a steeper scaling ∼k(⊥)⁻⁴ⁱ⁵. We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate.
Physical Review Letters 09/2010; 105(13):131101. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Using four-point measurements of the Cluster spacecraft, the energy distribution was determined for magnetic field fluctuations in the solar wind directly in the three-dimensional wave-vector domain in the range |k|<or=1.5x10{-3} rad/km. The energy distribution exhibits anisotropic features characterized by a prominently extended structure perpendicular to the mean field preferring the ecliptic north direction and also by a moderately extended structure parallel to the mean field. From the three-dimensional energy distribution wave vector anisotropy is estimated with respect to directions parallel and perpendicular to the mean magnetic field, and the result suggests the dominance of quasi-two-dimensional turbulence toward smaller spatial scales.
Physical Review Letters 04/2010; 104(17):171101. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster∕PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T⟂/T‖≳2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch‐angle scattering.
AIP Conference Proceedings. 03/2010; 1216(1):265-270.
-
[show abstract]
[hide abstract]
ABSTRACT: The three-component model of magnetic field fluctuations is applied to the analysis of the wave number spectra to study fluctuations
in the solar wind, the foreshock, and the magnetosheath. The analysis exhibits a transition of the dominant fluctuation component
from the solar wind to the magnetosheath, from the two-dimensional to the Alfvénic in the foreshock, and to the compressible
component in the magnetosheath.
12/2009: pages 363-368;
-
[show abstract]
[hide abstract]
ABSTRACT: 1] Observations of nongyrotropic electron distributions in the region upstream of the Earth's bow shock suggest that there exists a mechanism to lock in their phase, otherwise they would rapidly gyrophase mix into a ring-beam distribution. Measurements by the Plasma Electron and Current Experiment (PEACE) on the Cluster spacecraft have provided a way of determining the rotational period of a nongyrotropic electron distribution. For the time period studied, the rotational period is found to be %0.5 Hz, significantly lower than the local Larmor frequency but in line with the frequency of waves observed in the local magnetic field. Detailed wave analysis has revealed that the waves are most likely ordinary right-hand whistler waves. The conclusion is that the waves provide the necessary phase locking mechanism. It is not clear whether those waves are generated by the nongyrotropic distribution or are produced by other means and then cause the observed nongyrotropy., A phase locking mechanism for nongyrotropic electron distributions upstream of the Earth's bow shock, J. Geophys. Res., 110, A06206, doi:10.1029/2005JA011010.
01/2005;
-
[show abstract]
[hide abstract]
ABSTRACT: Coarse-grained information from a hybrid simulation show that previously developed quasifluid equations of state capture some aspects of proton cyclotron resonant interactions for parallel propagation in a low β plasma. Direct kinetic information is used as a closure for the information exchanged with the higher-order moment quantities. The coarse-graining procedure involves averaging over many proton-inertial lengths and looking at long time scales associated with the wave envelopes. By use of the coarse-graining prior to statistical analysis, the anticorrelations predicted by the equations of state are very high for both the single resonant wave case and for a broadband spectrum centered on a resonant wave. These anticorrelations are also consistent with what one expects from a single particle orbit analysis. A similar analysis, but done without the prior averaging procedures, shows no relevant correlations, and no simple dynamics emerges from the kinetic data in this case. A comparison is made with a model based on quasilinear theory. These results suggest that, in addition to simply taking velocity moments of particle distributions, the proper averaging of kinetic information over space and time scales lying below the range accessible to a fluid model can be essential to its success. © 1998 American Institute of Physics.
Physics of Plasmas 01/1998; 5(2):333-344. · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Using the four Cluster spacecraft, we have determined
the three-dimensional wave-vector spectra of fluctuating
magnetic fields in the solar wind. Three different solar
wind intervals of Cluster data are investigated for this purpose,
representing three different spatial scales: 10 000 km,
1000 km, and 100 km. The spectra are determined using the
wave telescope technique (k-filtering technique) without assuming
the validity of Taylor’s frozen-in-flow hypothesis nor
are any assumptions made as to the symmetry properties of
the fluctuations. We find that the spectra are anisotropic
on all the three scales and the power is extended primarily
in the directions perpendicular to the mean magnetic field,
as might be expected of two-dimensional turbulence, however,
the analyzed fluctuations are not axisymmetric. The
lack of axisymmetry invalidates some earlier techniques using
single spacecraft observations that were used to estimate
the percentage of magnetic energy residing in quasitwo-
dimensional power. However, the dominance of twodimensional
turbulence is consistent with the relatively long
mean free paths of cosmic rays in observed in the heliosphere.
On the other hand, the spectra also exhibit secondary
extended structures oblique from the mean magnetic field direction.
We discuss possible origins of anisotropy and asymmetry
of solar wind turbulence spectra.
Annales Geophysicae. 29(2011):1731-1738.
-
Journal of Geophysical Research, v.115 (2010).
