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The Science of SCOPE

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Turbulence

 

Transport in plasma occurs in physical, energy, and/or wave-number space and brings about plasma mixing, particle acceleration, and/or conversion or dissipation of energy. Turbulence often plays a crucial role in these transport processes, but because of its collisionless nature, transport in space plasma can exhibit very unique or anomalous features. SCOPE will unveil anomalous transport in collisionless plasma that most likely involves multi-scale physics and non-linearity, by attempting to answer the three key questions as follows:

image largeimage small Turbulence is likely to play an important role in substorm onset, which is one of the most dramatic phenomena in magnetospheric physics. The turbulence is of mulit-scale nature, ranging from MHD to electron-scale, and the key for unstanding the physics of the onset process is in uncovering how the processes at different scales couple.

1. How does turbulence transport energy over multiple scales?

A conventional theory of turbulence predicts that energy cascade (transport of energy from one spatial scale to another) occurs locally in wave-number space, namely via interaction of waves/vortices with similar wavelengths. In a space plasma such as the solar wind, however, waves with vastly different scales may couple, allowing for transport of energy directly from large- to small-scale and consequently for energy dissipation. SCOPE will uncover the energy cascade process in turbulent plasma whose dynamics may well be constrained under the influence of the magnetic field.

2. How does turbulence cause anomalous transport of collisionless plasma?

A conventional theory predicts that in the collisionless regime, no transport of particles occurs across the magnetic lines of force, but observations show that the solar wind enters the Earth’s magnetosphere across the barrier of the Earth’s magnetic field. SCOPE will reveal the ultimate mechanism (magnetic reconnection or turbulent diffusion) by which solar wind particles are transferred to the magnetosphere and how such microphysical processes become efficient during the course of the evolution of turbulent eddies of plasma.

3. What type of anomalous transport arises from the interaction between turbulence and non-uniform fields?

One of the most intriguing magnetospheric phenomena known as substorm rapidly converts and releases energy, and is believed to initiate in a non-uniform region of the magnetotail where macro- as well as micro-instabilities may get excited. SCOPE will answer the question of how various instabilities develop in such a non-uniform field and what anomalous effects does their turbulent growth bring about, for example, whether or not it causes a sudden structural or state transition of the magnetosphere that manifests in the ionosphere as an explosive expansion of aurora.