RECENT THEORETICAL RESULTS ON CORONAL HEATING DANIEL O. GOMEZ 1,∗ , PABLO A. DMITRUK 1,† and LEONARDO J. MILANO 2,† 1 Department of Physics, University of Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires, Argentina 2 National Solar Observatory, P.O.Box 62, Sunspot, NM 88349, U.S.A. (Received 20 September 1999; accepted 1 March 2000) Abstract. The scenario of magnetohydrodynamic turbulence in connection with coronal active re- gions has been actively investigated in recent years. According to this viewpoint, a turbulent regime is driven by footpoint motions and the incoming energy is efficiently transferred to small scales due to a direct energy cascade. The development of fine scales to enhance the dissipation of either waves or DC currents is therefore a natural outcome of turbulent models. Numerical integrations of the reduced magnetohydrodynamic equations are performed to simulate the dynamics of coronal loops driven at their bases by footpoint motions. These simulations show that a stationary turbulent regime is reached after a few photospheric times, displaying a broadband power spectrum and a dissipation rate consistent with the energy loss rates of the plasma confined in these loops. Also, the functional dependence of the stationary heating rate with the physical parameters of the problem is obtained, which might be useful for an observational test of this theoretical framework. 1. Introduction Recent X-ray and EUV observations of the solar corona reveal a highly structured brightness distribution, which is the consequence of magnetic fields confining the X-ray emitting plasma and governing its dynamics. Observations made with high spatial resolution (Schrijver et al., 1999; Golub et al., 1990; Golub and Pasachoff, 1997) show coronal magnetic loops with a highly filamentary internal structure. Coronal heating theories have traditionally been classified into two broad cate- gories: (a) AC or wave models, for which energy is provided by waves generated at the photosphere and, (b) DC or stress models, which assume that energy dissi- pates in magnetic stresses driven by slow footpoint motions. Although these two concepts seem mutually exclusive, the following assumptions are shared by both classes of models: (i) the ultimate source for coronal heating is the kinetic energy of the photospheric velocity field, (ii) the dissipation mechanism is Joule heating, although viscosity might also play an important role, (iii) the existence of fine structure in the coronal magnetic field is invoked to speed up Joule (or viscous) dissipation. Recent review articles on coronal heating (Narain and Ulmschneider, ∗ Also at: Instituto de Astronom´ ıa y F´ ısica del Espacio, C.C.67, Suc.28, 1428 Buenos Aires, Argentina. † Presently at: Bartol Research Institute, University of Delaware, Newark, DE 19716, U.S.A. Solar Physics 195: 299–318, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.