679 research outputs found
Characterization of the Turbulent Magnetic Integral Length in the Solar Wind: From 0.3 to 5 Astronomical Units
The solar wind is a structured and complex system, in which the fields vary
strongly over a wide range of spatial and temporal scales. As an example, the
turbulent activity in the wind affects the evolution in the heliosphere of the
integral turbulent scale or correlation length [{\lambda}], usually associated
with the breakpoint in the turbulent-energy spectrum that separates the
inertial range from the injection range. This large variability of the fields
demands a statistical description of the solar wind. In this work, we study the
probability distribution function (PDF) of the magnetic autocorrelation lengths
observed in the solar wind at different distances from the Sun. We use
observations from Helios, ACE, and Ulysses spacecraft. We distinguish between
the usual solar wind and one of its transient components (Interplanetary
Coronal Mass Ejections, ICMEs), and study also solar wind samples with low and
high proton beta [\beta_p ]. We find that in the last 3 regimes the PDF of
{\lambda} is a log-normal function, consistent with the multiplicative and
non-linear processes that take place in the solar wind, the initial {\lambda}
(before the Alfv\'enic point) being larger in ICMEs
Large-scale current systems and ground magnetic disturbance during deep substorm injections
We present a detailed analysis of the large-scale current systems and their effects on the
ground magnetic field disturbance for an idealized substorm event simulated with the
equilibrium version of the Rice Convection Model. The objective of this study is to evaluate
how well the bubble-injection picture can account for some classic features of the
substorm expansion phase. The entropy depletion inside the bubble is intentionally
designed to be so severe that it can penetrate deep into geosynchronous orbit. The
results are summarized as follows: (1) Both the region-1-sense and region-2-sense
field-aligned currents (FACs) intensify substantially. The former resembles the
substorm current wedge and flows along the eastern and western edges of the bubble.
The latter is connected to the enhanced partial ring current in the magnetosphere
associated with a dipolarization front earthward of the bubble. In the ionosphere, these
two pairs of FACs are mostly interconnected via Pedersen currents. (2) The horizontal
ionospheric currents show a significant westward electrojet peaked at the equatorward
edge of the footprint of the bubble. The estimated ground magnetic disturbance is
consistent with the typical features at various locations relative to the center of the westward
electrojet. (3) A prominent Harang-reversal-like boundary is seen in both ground DH
disturbance and plasma flow pattern, appearing in the westward portion of the equatorward
edge of the bubble footprint, with a latitudinal extent of 5 and a longitudinal extent of the
half width of the bubble. (4) The dramatic dipolarization inside the bubble causes the
ionospheric map of the inner plasma sheet to exhibit a bulge-like structure, which may be
related to auroral poleward expansion. (5) The remarkable appearance of the westward
electrojet, Harang-reversal-like boundary and poleward expansion starts when the
bubble reaches the magnetic transition region from tail-like to dipole-like
configuration. We also estimate the horizontal and vertical currents using magnetograms at
tens of ground stations for a deep injection substorm event occurred on April 9, 2008,
resulting in a picture that is qualitatively consistent with the simulation. Based on the
simulations and the observations, an overall picture of the ionospheric dynamics and its
magnetospheric drivers during deep bubble injections is obtained
Field-aligned currents observed by CHAMP during the intense 2003 geomagnetic storm events
International audienceThis study concentrates on the characteristics of field-aligned currents (FACs) in both hemispheres during the extreme storms in October and November 2003. High-resolution CHAMP magnetic data reflect the dynamics of FACs during these geomagnetic storms, which are different from normal periods. The peak intensity and most equatorward location of FACs in response to the storm phases are examined separately for both hemispheres, as well as for the dayside and nightside. The corresponding large-scale FAC peak densities are, on average, enhanced by about a factor of 5 compared to the quiet-time FACs' strengths. And the FAC densities on the dayside are, on average, 2.5 times larger in the Southern (summer) than in the Northern (winter) Hemisphere, while the observed intensities on the nightside are comparable between the two hemispheres. Solar wind dynamic pressure is correlated with the FACs strength on the dayside. However, the latitudinal variations of the FACs are compared with the variations in Dst and the interplanetary magnetic field component Bz, in order to determine how these parameters control the large-scale FACs' configuration in the polar region. We have determined that (1) the equatorward shift of FACs on the dayside is directly controlled by the southward IMF Bz and there is a saturation of the latitudinal displacement for large value of negative Bz. In the winter hemisphere this saturation occurs at higher latitudes than in the summer hemisphere. (2) The equatorward expansion of the nightside FACs is delayed with respect to the solar wind input. The poleward recovery of FACs on the nightside is slower than on the dayside. The latitudinal variations on the nightside are better described by the variations of the Dst index. (3) The latitudinal width of the FAC region on the nightside spreads over a wide range of about 25° in latitude
Correlation and Taylor scale variability in the interplanetary magnetic field fluctuations as a function of solar wind speed
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95101/1/jgra21350.pd
Micro-plasticity and intermittent dislocation activity in a simplified micro structural model
Here we present a model to study the micro-plastic regime of a stress-strain
curve. In this model an explicit dislocation population represents the mobile
dislocation content and an internal shear-stress field represents a mean-field
description of the immobile dislocation content. The mobile dislocations are
constrained to a simple dipolar mat geometry and modelled via a dislocation
dynamics algorithm, whilst the shear-stress field is chosen to be a sinusoidal
function of distance along the mat direction. The latter, defined by a periodic
length and a shear-stress amplitude, represents a pre-existing micro-structure.
These model parameters, along with the mobile dislocation density, are found to
admit a diversity of micro-plastic behaviour involving intermittent plasticity
in the form of a scale-free avalanche phenomenon, with an exponent for the
strain burst magnitude distribution similar to those seen in experiment and
more complex dislocation dynamics simulations.Comment: 30 pages, 12 figures, to appear in "Modelling and Simulation in
Materials Science and Engineering
Hadron Spectroscopy with COMPASS at CERN
The aim of the COMPASS hadron programme is to study the light-quark hadron
spectrum, and in particular, to search for evidence of hybrids and glueballs.
COMPASS is a fixed-target experiment at the CERN SPS and features a two-stage
spectrometer with high momentum resolution, large acceptance, particle
identification and calorimetry. A short pilot run in 2004 resulted in the
observation of a spin-exotic state with consistent with the
debated . In addition, Coulomb production at low momentum transfer
data provide a test of Chiral Perturbation Theory. During 2008 and 2009, a
world leading data set was collected with hadron beam which is currently being
analysed. The large statistics allows for a thorough decomposition of the data
into partial waves. The COMPASS hadron data span over a broad range of channels
and shed light on several different aspects of QCD.Comment: 4 pages, 5 figure
Recommended from our members
Hadron spectroscopy and B physics at RHIC
A description is given of the physics opportunities at RHIC regarding quark-gluon spectroscopy. The basic idea is to isolate with appropriate triggers the sub-processes pomeron + pomeron {yields} hadrons and {gamma}{sup *} + {gamma}{sup *} {yields} hadrons with the net effective mass of hadrons in the range of 1.0 to 10.0 GeV, in order to study the hadronic states composed of quarks and gluons. The double-pomeron interactions are expected to produce glueballs and hybrids preferentially, while the two-offshell-photon initial states should couple predominantly to quarkonia and multiquark states. Of particular interest is the possibility of carrying out a CP-violation study in the self-tagging B decays, B{sub d}{sup 0} {yields} K{sup +}{pi}{sup {minus}} and {bar B}{sub d}{sup 0} {yields} K{sup {minus}}{pi}{sup +}. 20 refs., 4 figs
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Double-Pomeron and two-photon processes at RHIC
Double-Pomeron processes have been shown to be an important and novel source of hadron production at moderate energies at the ISR. These processes are expected to provide glue-rich hadrons from 1 GeV to 10 GeV or more, encompassing the states consisting of u, d, s and b quarks. The double-pomeron cross sections for central hadroproduction are calculated for p {times} p and Au {times} Au at RHIC. Two-photon production of hadrons in the central region begins to dominate or at least become comparable to the double-Pomeron processes as the Z of the beams increases from p to Au. Since photons couple to charge, these hadroproductions involve mainly quarkonia and multiquark states. Therefore, a comparative study of these processes is expected to provide new insights into the constituents of hadronic matter. The two-photon processes are calculated following the recipe given by Cahn and Jackson. The paper starts out with a thorough discussion of the relevant kinematics, phase space and Regge amplitudes
Changes in the response of the AL Index with solar cycle and epoch within a corotating interaction region
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