Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-mode Excitation

Abstract

It has been suggested that the Z-mode instability driven by energetic electrons with a loss-cone type velocity distribution is one candidate process behind the continuum and zebra pattern of solar type-IV radio bursts. Both the temperature of background plasma ( T 0 ) and the energy of energetic electrons ( v e ) are considered to be important to the variation of the maximum growth rate ( γ max ). Here we present a detailed parameter study on the effect of T 0 and v e , within a regime of the frequency ratio ( ). In addition to γ max , we also analyze the effect on the corresponding wave frequency ( ) and propagation angle ( θ max ). We find that (1) γ max generally decreases with increasing v e , while its variation with T 0 is more complex depending on the exact value of v e . (2) With increasing T 0 and v e , presents stepwise profiles with jumps separated by gradual or very weak variations, and due to the warm plasma effect on the wave dispersion relation can vary within the hybrid band (the harmonic band containing the upper hybrid frequency) and the higher band. (3) The propagation is either perpendicular or quasi-perpendicular, and θ max presents variations in line with those of , as constrained by the resonance condition. We also examine the profiles of γ max with for different combinations of T 0 and v e to clarify some earlier calculations which show inconsistent results.