Plasma physics challenge: confirm new plasma wave mode predicted by space physics

摘要

Summary form only given. A new plasma wave mode has been proposed to explain plasma emissions stimulated by satellite-borne high-power radio-frequency sounders designed to derive remote electron density profiles from electromagnetic-wave echoes. These sounders also generate electrostatic waves that produce coherent echoes (called plasma resonances because of their appearance on the data records) that occur near harmonics of the electron cyclotron frequency f/sub ce/, the electron plasma frequency f/sub pe/, and the upper-hybrid frequency f/sub uh/, where f/sub uh//sup 2/=f/sub pe//sup 2/+f/sub ce//sup 2/. They also stimulate plasma emissions, at frequencies related to these characteristic frequencies, including a sequence observed at frequencies below f/sub pe/ and between the f/sub ce/ harmonics. They are known as the Dn resonances because of their diffuse appearance on ionospheric topside-sounder records where they were first observed nearly forty years ago. Five mechanisms have been proposed to explain these resonances. One, based on eigenmodes of cylindrical electromagnetic plasma oscillations , predicts the observed frequency spacing of the observed Dn sequence and also that these resonances would be expected in any magnetized plasma where f/sub pe/ and f/sub ce/ are comparable. In agreement with these predictions the Dn resonances have been stimulated in other space plasmas, including the magnetosphere in spite of much different f/sub pe/, f/sub ce/ and electron temperature values, the main controlling parameter being the ratio f/sub pe//f/sub ce/. An empirical fit to ionospheric topside sounder observations yields f/sub D1/=0.95 (f/sub pe/f/sub ce/)/sup 1/2/. The main challenge remaining is to derive this fundamental frequency, i.e., for n=1 which is most prominently observed when f/sub pe//f/sub ce//spl ap/2-4, from kinetic theory (analytically or by numerical simulations) and verify using laboratory experiments.