THE EFFECTS OF KELVIN-HELMHOLTZ INSTABILITY ON RESONANCE-ABSORPTION LAYERS IN CORONAL LOOPS

One of the long-standing uncertainties in the wave-resonance theory of coronal heating is the stability of the resonance layer. The wave mot ions in the resonance layer produce highly localized shear flows which vary sinusoidally in time with the resonance period. This configurati on is potentially susceptible to the Kelvin-Helmholtz instability (KHI ), which can enhance small-scale structure and turbulent broadening of shear layers on relatively rapid ideal timescales. We have investigat ed numerically the response of a characteristic velocity profile, deri ved from resonance absorption models, to finite fluid perturbations co mparable to photospheric fluctuations. We find that the KHI primarily should affect long (greater than or similar to 6 x 10(4) km) loops whe re higher velocity flows (M greater than or similar to 0.2) exist in r esonance layers of order 100 km wide. There, the Kelvin-Helmholtz grow th time is comparable to or less than the resonance quarter-period, an d the potentially stabilizing magnetic effects are not felt until the instability is well past the linear growth stage. Not only is the reso nance layer broadened by the KHI, but also the convective energy trans port out of the resonance layer is increased, thus adding to the effic iency of the wave-resonance heating process. In shorter loops, e.g., t hose in bright points and compact flares, the stabilization due to the magnetic field and the high resonance frequency inhibit the growth of the Kelvin-Helmholtz instability beyond a minimal level.