D resonances as eigenmodes of magnetized plasma

Summary form only given. The first diffuse resonance (D1) was discovered by Nelms and Lockwood in the spectrum generated by a topside sounder on the Alouette 2 spacecraft. They interpreted the frequency of D1 as 3/2 f/sub ce/, where f/sub ce/ is the electron gyro frequency. Further observations indicated that f/sub D1/ was dependent on f/sub pe//f/sub ce/ where f/sub pe/ is the electron plasma frequency. The hypothesis that the D resonances are electron eigenmodes has led to the following equations describing the frequencies for Dn and subsidiary resonances: f/sub Dn/=0.95(f/sub pe/f/sub ce/)/sup 1/2/n/sup 1/2/ f/sub Dn//sup +/=(f/sub Dn//sup 2/+f/sub ce//sup 2/)/sup 1/2/ f/sub Dn//sup -/=(f/sub Dn//sup 2/-f/sub ce//sup 2/)/sup 1/2/ where n=1,2,.... These formulas, based on a combined theoretical and empirical approach, describe a /spl radic/n spectrum with each mode split by the magnetic field analogous to the Zeeman splitting in quantum mechanics. The /spl radic/n spectrum was first predicted by Osherovich. A major challenge remains to derive the fundamental f/sub Dn/ frequency from first principles.