The universally growing mode in the solar atmosphere: coronal heating by drift waves

Abstract

The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid and kinetic drift wave theory. We show that the basic ingredient necessary for the heating is the presence of density gradients in the direction perpendicular to the magnetic field vector. Such density gradients are a source of free energy for the excitation of drift waves. We use only well‐established basic theory, verified experimentally in laboratory plasmas. Two mechanisms of the energy exchange and heating are shown to take place simultaneously: one due to the Landau effect in the direction parallel to the magnetic field, and another one, stochastic heating, in the perpendicular direction. The stochastic heating (i) is due to the electrostatic nature of the waves, (ii) is more effective on ions than on electrons, (iii) acts predominantly in the perpendicular direction, (iv) heats heavy ions more efficiently than lighter ions and (v) may easily provide a drift wave‐heating rate that is orders of magnitude above the value that is presently believed to be sufficient for the coronal heating, that is ≃6 × 10−5 J m−3 s−1 for active regions and ≃8 × 10−6 J m−3 s−1 for coronal holes. This heating acts naturally through well‐known effects that are, however, beyond the current standard models and theories.

Kinetic Instability of Drift-Alfvén Waves in Solar Corona and Stochastic Heating

“…In a typical realistic geometry, e.g., in a laboratory plasma or in the magnetic structures in the corona, the x-coordinate would correspond to the radial direction, the y-coordinate to the poloidal direction, and the z-coordinate to the axial direction. More details on this are available in Vranjes & Poedts (2009b). Additional inhomogeneities of the magnetic field and the temperature introduce the reactive-type η i -instability discussed in detail in Vranjes & Poedts (2009c).…”

“…The characteristic diffusion time is in fact orders of magnitude above the drift-wave growth time. More details on that issue are available in Vranjes & Poedts (2008, 2009b.…”

“…In the limit of a negligible ion response along the magnetic field vector, |ω r /k z | c s with c 2 s = κT e /m i , and for small gravity effects, this gives the ES drift-wave frequency used in Vranjes & Poedts (2009a, 2009b, 2009c, 2009d:…”

“…In our recent papers (Vranjes & Poedts 2009a, 2009b, 2009c, 2009d a novel approach and a new paradigm for the coronal heating has been put forward. The model is based on the driftwave theory, a well-known subject in the general plasma theory, in laboratory plasma physics, and even in terrestrial ionospheric research (Kelley 1989).…”

“…The nature of the heating is such that it essentially acts in the perpendicular direction, and, in addition to this, more massive particles are in fact more effectively heated by that mechanism. The analysis performed in Vranjes & Poedts (2009a, 2009b, 2009c, 2009d was focused on the electrostatic (ES) domain of the drift-wave instability. This implies a small plasma-β = 2μ 0 n 0 κT /B 2 0 , e.g., of the order or below m e /m i .…”