26 research outputs found
Inverse cascade in the structure of substorm aurora and non-linear dynamics of field-aligned current filaments
We investigate time evolution of scaling index αA that characterizes
auroral luminosity fluctuations at the beginning of substorm expansion. With
the use of UVI images from the Polar satellite, it is shown that αA
typically varies from values less than unity to ~1.5, increasing with
breakup progress. Similar scaling features were previously reported for
fluctuations at smaller scales from all-sky TV observations. If this
signature is interpreted in terms of non-linear interactions between scales,
it means that the power of small-scale fluctuations is transferred with time
to larger scales, a kind of the inverse cascade. Scaling behavior in the
aurora during substorm activity is compared with that in the field-aligned
currents simulated numerically in the model of non-linear interactions of
Alfvénic coherent structures, according to the Chang et al. (2004) scenario.
This scenario also suggests an inverse cascade, manifesting in clustering of
small-scale field-aligned current filaments of the same polarity and
formation of "coarse-grained" structures of field-aligned currents
Anomalous behavior of cutoff rigidity variation in the region of the Mexico station during a magnetic superstorm on 20 November 2003
The pioneering storm-time model of magnetospheric magnetic field T01S made
possible trajectory calculations for the events of giant magnetic storms. We
have performed such calculations for a unique magnetic storm on 20 November
2003. In our previous paper, Belov et al. (2005), dedicated to the
magnetospheric effects of cosmic rays (CR) during this storm, we revealed an
anomalous behavior of a cutoff rigidity variation at the Mexico station. Here,
by trajectory calculations, we demonstrate that this peculiarity persists in
the latitudinal and longitudinal curves of cutoff rigidity (Rc) for both
quiet and storm-time conditions and thus should be considered as physically
meaningful
Simulation of the interchange instability in a magnetospheric substorm site
We perform modeling of the interchange instability driven by longitudinal pressure asymmetry in the region of the pressure buildup that forms in the inner magnetosphere at the substorm growth phase. The simulation refers to the dawnward side of the Harang discontinuity and times after <i>B<sub>z</sub></i> IMF turning northward. The solution for the equilibrium state indicates tailward flows associated with vortices, which is in agreement with a previous finding of Ashour-Abdalla et al.&nbsp;(1999, 2002). We show that in the regions of equilibrium field-aligned currents (FACs), small initial perturbations in <i>pV</i><sup>&gamma;</sup> (<i>p</i> is the isotropic plasma pressure, <i>V</i> is the unit magnetic flux tube volume, &gamma;=5/3 the adiabatic exponent), set up as ripples inclined to azimuth, grow in time. For the background FAC of ~10<sup>-6</sup> A/m<sup>2</sup>, the linear growth rate of the instability is ~6 min. Starting from the 12th&nbsp;min of evolution, the perturbations exhibit nonlinear deformations, develop undulations and front steepening. An interesting peculiarity in the distribution of the associated small-scale FACs is that they become asymmetric with time. Specifically, the downward currents are more localised, reaching densities up to 15&times;10<sup>-6</sup> A/m<sup>2</sup> at the nonlinear stage. The upward FACs are more dispersed. When large enough, these currents are likely to produce the aurora. We also run our simulation for the initial perturbations of large transverse scales in order to demonstrate that the interchange instability can be responsible for pressure and cross-tail current spatial variations of great extent