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  • 1
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    Magnetohydrodynamic Turbulence and Reconnection in the Magnetotail (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: We have used a global MHD simulation with high spatial resolution to investigate the origin and properties of turbulence in the plasma sheet. In this simulation we imposed a steady southward IMF with a magnitude of 5 nT at the upstream simulation boundary for more than three hours followed by ninety minutes of northward IMF of the same magnitude. The solar wind number density was 20 cm-3, the thermal pressure was 20 pPa, and the velocity was 500 km/s in the x direction. The moderately high dynamic pressure confined the magnetotail to the high-grid resolution region. Even for these nominal solar wind parameters and steady driving the plasma sheet became turbulent. The power spectral densities and probability distribution functions computed from the simulations were comparable to those obtained from spacecraft observations. The largest scale vortices were associated with reconnection outflows and, in the southward IMF case, with the diversion of high speed flows in the near-Earth region. Both time and space domain analyses revealed that there were three scales present, the large scale of the driving processes, the intermediate inertial scale and the dissipative scale.
    Keywords: Space Sciences (General)
    Type: SM53A-06 , GSFC.ABS.5719.2011 , American Geophysical Union (AGU) 2011 Fall Meeting; Dec 05, 2011 - Dec 09, 2011; San Francisco, CA; United States
    Format: application/pdf
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  • 2
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    Cluster Observations of Multiple Dipolarization Fronts (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1-3, are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multi-spacecraft timing analysis, DF normals are found to propagate mainly earthward at $160-335$ km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the $x$ and $y$ components of the magnetic field whose peaks are found 1-2 minutes after the DF passage. These $(B_{x},B_{y} )$-fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with $(B_{x},B_{y})$ fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux-tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the mid-tail magnetic topology. This process generates significant field-aligned currents, and might power the auroral brightening in the ionosphere. However, this event is neither associated with the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.
    Keywords: Geosciences (General)
    Type: SM11D-04 , GSFC.ABS.5713.2011 , American Geophysical Union 2011 Fall Meeting; Dec 04, 2011 - Dec 09, 2011; San Francisco, CA; United States
    Format: application/pdf
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  • 3
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    Theory and Simulations of Solar System Plasmas (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: "Theory and simulations of solar system plasmas" aims to highlight results from microscopic to global scales, achieved by theoretical investigations and numerical simulations of the plasma dynamics in the solar system. The theoretical approach must allow evidencing the universality of the phenomena being considered, whatever the region is where their role is studied; at the Sun, in the solar corona, in the interplanetary space or in planetary magnetospheres. All possible theoretical issues concerning plasma dynamics are welcome, especially those using numerical models and simulations, since these tools are mandatory whenever analytical treatments fail, in particular when complex nonlinear phenomena are at work. Comparative studies for ongoing missions like Cassini, Cluster, Demeter, Stereo, Wind, SDO, Hinode, as well as those preparing future missions and proposals, like, e.g., MMS and Solar Orbiter, are especially encouraged.
    Keywords: Space Sciences (General)
    Type: European Geosciences Union General Assembly 2011; Apr 02, 2011 - Apr 09, 2011; Vienna; Austria
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  • 4
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    Observations and Interpretation of Magnetofluid Turbulence at Small Scales (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: High time resolution magnetic field measurements from the four Cluster spacecraft have revealed new features of the properties of magnetofluid turbulence at small spatial scales; perhaps even revealing the approach to the dissipation regime at scales close to the electron inertial length. Various analysis techniques and theoretical ideas have been put forward to account for the properties of those measurements. The talk will describe the current state of observations and theory, and will point out on-going and planned research that will further our understanding of how magnetofluid turbulence dissipates. The observations and theories are directly germane to studies being planned as part of NASA's forthcoming Magnetospheric Multiscale Mission.
    Keywords: Space Sciences (General)
    Type: GSFC.ABS.5718.2011 , American Geophysical Union (AGU) 2011 Fall Meeting; Dec 05, 2011 - Dec 09, 2011; San Francisco, CA; United States
    Format: application/pdf
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