Energy cascade rate measured in a collisionless space plasma with MMS data and compressible Hall magnetohydrodynamic turbulence theory. (arXiv:1911.09749v1 [physics.plasm-ph])
<a href="http://arxiv.org/find/physics/1/au:+Andres_N/0/1/0/all/0/1">Nahuel Andrés</a>, <a href="http://arxiv.org/find/physics/1/au:+Sahraoui_F/0/1/0/all/0/1">Fouad Sahraoui</a>, <a href="http://arxiv.org/find/physics/1/au:+Galtier_S/0/1/0/all/0/1">Sebastien Galtier</a>, <a href="http://arxiv.org/find/physics/1/au:+Hadid_L/0/1/0/all/0/1">Lina Z. Hadid</a>, <a href="http://arxiv.org/find/physics/1/au:+Ferrand_R/0/1/0/all/0/1">Renaud Ferrand</a>, <a href="http://arxiv.org/find/physics/1/au:+Huang_S/0/1/0/all/0/1">Shiyong Y. Huang</a>
The first complete estimation of the compressible energy cascade rate
$|varepsilon_text{C}|$ at magnetohydrodynamic (MHD) and sub-ion scales is
obtained in the Earth’s magnetosheath using Magnetospheric MultiScale (MMS)
spacecraft data and an exact law derived recently for {it compressible} Hall
MHD turbulence. A multi-spacecraft technique is used to compute the velocity
and magnetic gradients, and then all the correlation functions involved in the
exact relation. It is shown that when the density fluctuations are relatively
small, $|varepsilon_text{C}|$ identifies well with its incompressible
analogue $|varepsilon_text{I}|$ at MHD scales but becomes much larger than
$|varepsilon_text{I}|$ at sub-ion scales. For larger density fluctuations,
$|varepsilon_text{C}|$ is larger than $|varepsilon_text{I}|$ at every scale
with a value significantly higher than for smaller density fluctuations. Our
study reveals also that for both small and large density fluctuations, the
non-flux terms remain always negligible with respect to the flux terms and that
the major contribution to $|varepsilon_text{C}|$ at sub-ion scales comes from
the compressible Hall flux.
The first complete estimation of the compressible energy cascade rate
$|varepsilon_text{C}|$ at magnetohydrodynamic (MHD) and sub-ion scales is
obtained in the Earth’s magnetosheath using Magnetospheric MultiScale (MMS)
spacecraft data and an exact law derived recently for {it compressible} Hall
MHD turbulence. A multi-spacecraft technique is used to compute the velocity
and magnetic gradients, and then all the correlation functions involved in the
exact relation. It is shown that when the density fluctuations are relatively
small, $|varepsilon_text{C}|$ identifies well with its incompressible
analogue $|varepsilon_text{I}|$ at MHD scales but becomes much larger than
$|varepsilon_text{I}|$ at sub-ion scales. For larger density fluctuations,
$|varepsilon_text{C}|$ is larger than $|varepsilon_text{I}|$ at every scale
with a value significantly higher than for smaller density fluctuations. Our
study reveals also that for both small and large density fluctuations, the
non-flux terms remain always negligible with respect to the flux terms and that
the major contribution to $|varepsilon_text{C}|$ at sub-ion scales comes from
the compressible Hall flux.
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