19 research outputs found
Fast changes of energetic particle intensity near the boundary between the magnetotail and trapped region during substorm activations
Cellular automata model of magnetospheric-ionospheric coupling
We propose a cellular
automata model (CAM) to describe the substorm activity of the
magnetospheric-ionospheric system. The state of each cell in the model is
described by two numbers that correspond to the energy content in a region of
the current sheet in the magnetospheric tail and to the conductivity of the
ionospheric domain that is magnetically connected with this region. The driving
force of the system is supposed to be provided by the solar wind that is
convected along the two boundaries of the system. The energy flux inside is
ensured by the penetration of the energy from the solar wind into the array of
cells (magnetospheric tail) with a finite velocity. The third boundary (near to
the Earth) is closed and the fourth boundary is opened, thereby modeling the
flux far away from the tail. The energy dissipation in the system is quite
similar to other CAM models, when the energy in a particular cell exceeds some
pre-defined threshold, and the part of the energy excess is redistributed
between the neighbouring cells. The second number attributed to each cell
mimics ionospheric conductivity that can allow for a part of the energy to be
shed on field-aligned currents. The feedback between "ionosphere" and
"magnetospheric tail" is provided by the change in a part of the
energy, which is redistributed in the tail when the threshold is surpassed. The
control parameter of the model is the z-component of the interplanetary
magnetic field (Bz IMF), "frozen" into the solar wind. To study the
internal dynamics of the system at the beginning, this control parameter is
taken to be constant. The dynamics of the system undergoes several
bifurcations, when the constant varies from - 0.6 to - 6.0. The Bz IMF input
results in the periodic transients (activation regions) and the inter-transient
period decreases with the decrease of Bz. At the same time the onset of
activations in the array shifts towards the "Earth". When the modulus
of the Bz IMF exceeds some threshold value, the transition takes place from
periodic to chaotic dynamics. In the second part of the work we have chosen as
the source the real values of the z-component of the interplanetary magnetic
field taken from satellite observations. We have shown that in this case the
statistical properties of the transients reproduce the characteristic features
observed by Lui et al. (2000).Key words. Magnetospheric physics
(magnetosphere-ionosphere interactions) – Space plasma physics (nonlinear
phenomena
CELLULAR MODEL ANALOGY OF THE MAGNETOSPHERE-IONOSPHERE SUBSTORM ACTIVITY DRIVEN BY SOLAR WIND WITH FINITE VELOCITY OF PENETRATION INTO MAGNETOSPHERE
Abstract. The cellular model as an analogy of the dynamical magnetosphere-ionosphere system related with the substorm activity is presented. Each cell in the model contains two connected parts, one of which may be associated with the magnetosphere current sheet piece, and other -with the ionosphere region at the same magnetic field tube. The local positive feedback between magnetospheric and ionospheric parts of each cell has been included in the model. The magnetospheric part of the model system is organised as a rectangular cellular automation with local redistribution of the stored energy from the cells where the threshold value is exceeded. We suppose that the threshold value in each cell depends on external control parameter which influences the long boundaries of the rectangular array. The finite velocity is assumed for the influence penetration into the array and along boundaries. Internal rules in the model are fully deterministic: there is not used any random number. As an external control parameter of the model we consider the z-component of interplanetary magnetic field (B z IMF) which is «freezed» in the solar wind. Dynamics of the model for constant control parameter and for driving by real B z IMF is discussed. The model demonstrates two types of transients. The characteristics of the transients are discussed
Changes in the magnetospheric cross-field current during substorm expansion phase as observed by CRRES
CRRES observations of local tailward stretchings of the geomagnetic field at 6.3 < L < 6.7 during the substorm expansion phase
Investigation of the conjugacy between auroral breakup and energetic electron injection.
CosRes2_07LazutinLO
Abstract -In the first part of this study of the substorm of March 12, 1991, the space-time structure of substrorm disturbance and dynamics of auroral ions were considered. This second part presents an analysis of measurements of auroral electrons onboard the CRRES satellite. It is demonstrated that enhancements of the electron flux (injections) during large-scale and local dipolarizations of the magnetic field are determined by a combination of field-aligned, induction, and betatron mechanisms of acceleration with an effect of displacement of the drift shells of particles. The relative contributions of these mechanisms in relation to the energy of auroral electrons are determined. PACS: 94.30.Lr, 94.30.Aa, 94.20.A
Observations of substorm fine structure
Particle and magnetic field measurements on
the CRRES satellite were used, together with geosynchronous satellites and
ground-based observations, to investigate the fine structure of a magnetospheric
substorm on February 9, 1991. Using the variations in the electron fluxes, the
substorm activity was divided into several intensifications lasting about 3–15
minutes each. The two main features of the data were: (1) the intensifications
showed internal fine structure in the time scale of about 2 minutes or less. We
call these shorter periods activations. Energetic electrons and protons at the
closest geosynchronous spacecraft (1990 095) were found to have comparable
activation structure. (2) The energetic (>69 keV) proton injections were
delayed with respect to electron injections, and actually coincided in time with
the end of the intensifications and partial returns to locally more stretched
field line configuration. We propose that the energetic protons could be able to
control the dynamics of the system locally be quenching the ongoing
intensification and possibly preparing the final large-scale poleward movement
of the activity. It was also shown that these protons originated from the same
intensification as the preceeding electrons. Therefore, the substorm instability
responsible for the intensifications could introduce a negative feedback loop
into the system, creating the observed fine structure with the intensification
time scales.Key words. Magnetospheric Physics (Storms and
substorms)