Eun-Hwa Kim, Iver. H. Cairns and Jay R. Johnson
Linear mode conversion of Langmuir/ to electromagnetic near the plasma and upper hybrid frequency in the presence of density gradients is potentially relevant to type II and III solar radio bursts, ionospheric radar experiments, pulsars, and continuum for planetary magnetospheres. Here, we study mode conversion in warm, using a numerical electron fluid simulation code when the density gradient has a wide range of angle, , to the ambient , for a range of incident Langmuir/ wavevectors. Our results include: (1) Left-handed polarized ordinary () and right-handed polarized extraordinary () mode are produced in various ranges of for Ω = ()1 3() < 1.5, whereis the (angular) electron cyclotron frequency, is the angular frequency, is the length scale of the (linear) density gradient, and is the speed of light; (2) the mode is produced most strongly in the range, 40° < < 60°, for intermediately with Ω = 1.0 and 1.5, while it is produced over a wider range, 0° ≤ ≤ 90°, for weakly with Ω = 0.1 and 0.7; (3) the maximum total conversion efficiencies for power from the Langmuir/ mode to are of order 50%99% and the corresponding conversion efficiencies are 5%14% (depending on the adiabatic index and = / 2, where is the electron temperature and is the electron) for various Ω; (4) the mode conversion window becomes wider as Ω and increase. Hence, the results in this paper confirm that linear mode conversion under these conditions can explain the weak total circular of interplanetary type II and III solar radio bursts because a strong mode can be generated via linear mode conversion near ∼ 45°.