I just read an interesting paper by Smith et al. (2012, ApJ), where they describe four characteristic regions in the power spectra of turbulent magnetic field fluctuations:
1. f < 0.5 Hz: Ion Inertial Range, Spectral Index (SI) ~ 5/3
2. f \in [0.2,3] Hz: Ion Dissipation Range, SI ~ 3, generally steeper than 1 & 3
3. f \in [3,30] Hz: Electron Inertial Range, SI ~ 2.5
4. f > 30 Hz: Electron Dissipation Range, steeper than 3
My question is: What exacly controls the extent of the ion dissipation range and how can it be distinguished from the electron inertial scale?
Looking at a lot of observations of turbulence in the solar wind, one finds that the ion inertial range seems to directly turn into the electron inertial range, without showing characteristics of a steeper ion dissipation range. E.g. in the papers by Alexandrova et al. (2009, Phys.Rev.Let.), Sahraoui et al. (2009, Phys.Rev.Let.) and Bourouaine et al. (2012, ApJ) the ion dissipation range is either very small or even non-existent.
Also there are a lot of turbulence models, that do not take the ion dissipation range into account but rather go directly from Alfven wave turbulence to kinetic Alfven wave (KAW), whistler or Hall-MHD turbulence, e.g. the weakened cascade model by Howes et al. (2011, Phys.Plas.) or the Hall-MHD model by Galtier (2006, J.Plas.Phys.).
To my knowledge there are only few papers that deal with the ion dissipation range in detail, such as Voitenko & Keyser (2011, NL Proc. in Geoph.), who call this range the weakly dispersive range and explain it with non-linear interactions of KAW that can produce very steep slopes up to SI~5.
So much for the background. Now I would like to know: What are your thoughts on this? Have you encountered problems regarding ion dissipation? Do you know how to identify ion dissipation and electron inertial ranges in your data? What do you think controls the ion dissipation range? Why is it sometimes there and sometimes not?
I thought pick-up ions are responsible in large part for the dissipation at the termination termination shock. The pick-up ions are at most 20 percent the number density of the thermal ions, but their pressure dominates the thermal pressure.
see: e.g. Zank, G.P. 1999, Space Science Reviews, Issue 3/4 p. 413-688:
Interaction of the solar wind with the local interstellar medium, a theoretical perspective.
Gary Webb: CSPAR, Univ. of Alabama in Huntsville.
Agree with Gary on the pick-up ions but why not also try a quasi-linear dissipation on the cyclotron resonance with thermal ions? Will depend on the local ion distribution function (that's why the observed slopes vary?). Are there measurements of the ion PDFs associated with the different spectral slopes observed? Particle mirroring on quasi-periodic structures, QL plateau formation may dissipate the MHD cascade quite efficiently in this range.
in my recent paper I have, between others, introduced a new physical property: thermal natural frequency and explained the solar wind phenomenon
https://www.researchgate.net/profile/Dimis_Poulos