MHD structures, waves and turbulence in the solar wind: Observations and theories

Dissipation and heating in solar wind turbulence: from the macro to the micro and back again

“…Among the scientific observations of astrophysical plasma that are available to us, the solar wind provides an excellent laboratory for the study of fully developed plasma turbulence. The solar wind and the near-Earth environment are also the only in situ observationally accessible highly turbulent plasmas [1][2][3] with magnetic Reynolds numbers of the order of 10 5 [4] at 1 AU. In situ spacecraft observations from both field and particle instruments, show highly developed turbulence at 1 AU.…”

Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

“…In this view the fluctuations are described as non-interacting Alfvén waves along with an admixture of classical MHD discontinuities that advect with the wind [80,97]. This perspective stands in contrast to a number of features of interplanetary observations that are consistent with an active turbulence cascade, including, for example, reduction of Alfvénicity, lowering of the Alfvén ratio, development of anisotropy, evolution of the correlation scale [98,99], observed plasma heating [100,101] and the direct measurement of cascade rates [18,102,103]. The recent revival of the so-called spaghetti model of solar wind flux tubes [65,104,105] treats flux tubes and their boundaries, which are static discontinuities, as inert remnants of coronal processes.…”

Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma Instabilities

“…Our use of linear theory is motivated in part by the argument that strongly turbulent fluctuations in a plasma retain certain properties associated with linear modes Salem et al 2012;Chen et al 2013;Howes et al 2014). Observations in the solar wind show that dn p and | | d B are anticorrelated (Belcher & Davis 1971;Bavassano & Bruno 1989;Tu & Marsch 1995;Chernyshov et al 2008;Yao et al 2011;Howes et al 2012;Klein et al 2012;Kiyani et al 2013), and we consequently take the large-scale compressions to be solutions to the hot-plasma dispersion relation for which dn p and | | d B are anticorrelated. We refer to such solutions as "kinetic slow modes."…”

“…After some algebra, we obtain the following expressions for the differentials that describe the effect of fluctuations in B and n p on R p and  b p : For the sake of simplicity, we take our equilibrium state to be isotropic and approximate the wave-polarization properties using isotropic MHD, which yields defines the phase speed of the fast (upper sign) and slow (lower sign) magnetosonic mode in units of the Alfvén speed v A , and where κ is the specific heat ratio (see also Marsch 1986;Tu & Marsch 1995). Figure 6 shows the hodogram of a plasma parcel in the - , which we have constructed with Equations (32) and (33) using the thresholds from Equation (5).…”