Volume 148, number 5 PHYSICS LETTERS A 20 August 1990 Electromagnetic radiation generation in an inhomogeneous magnetized plasma Hamid Saleem’ Institute for Theoretical Physics, Department ofPhysics and Astronomy, Ruhr-University Bochum, D-4630 Bochum, FRG and G. Murtaza Department of Physics, Quaid-I-Azam University, Islamabad, Pakistan Received 1 August 1989; revised manuscript received 10 April 1990; accepted for publication 12 June 1990 Communicated by R.C. Davidson The parametric decay ofthe electrostatic upper-hybrid wave into ordinary and extraordinary electromagnetic radiation and the electron convection mode in an inhomogeneous weakly magnetized dense plasma is studied. The large growth rate values as compared to our earlier work indicate that this is an important decay process responsible for the generation of enhanced narrow band radiation observed in the earth’s magnetosphere. Several authors [1—7] have suggested different mechanisms for the generation of terrestrial nonthermal con- tinuum radiation. It is important to note that this electromagnetic radiation is always accompanied by some intense electrostatic waves observed near the upper-hybrid (UH) frequency, the field is ~ 1 mV/rn. The si- multaneous existence of the two suggests a causal relationship between them. There is now a general consensus that the intense electrostatic upper-hybrid wave converts into electromagnetic radiation by some linear or non- linear process [5]. Since observations [8] reveal narrow, relatively intense lines in the radiation spectrum, Murtaza and Shukia [6] pointed out that coherent conversion may also act at times. They proposed that the radiation could have been generated by a parametric decay process of the upper-hybrid wave. Their calculations presented that the upper-hybrid pump wave can parametrically decay into a perpendicularly (to an external magnetic field B 0) propagating electrostatic lower-hybrid/ion-cyclotron wave and a left handed circularly polarized (LHCP) elec- tromagnetic wave (along B0) or an ordinary mode radiation (across B0). Although there is no definitive state- ment with regard to the polarization of the radiation, the observations do indicate the existence of both 0- mode and X-mode radiation [5]. Therefore, Saleem et a!. [71 showed that UHW can also parametrically excite the X-mode radiation accompanied by some low-frequency mode. The low-frequency modes are not known exactly in the source region. Therefore, a number of test waves were tried as low-frequency counterparts in the decay process of UHW which include: lower-hybrid wave, ion-cyclotron wave, electron acoustic wave and shear Alven wave. They also presented a comparison of growth rates of different decay processes. The minimum e- folding time turned out to be of the order of a fraction of a second for the plasma parameters in the source region. Permanent addresses: (1) NPD, PINSTECH, P.O. Nilore, Islamabad, Pakistan; (2) Department of Physics, Quaid-i-Azam Univer- sity, Islamabad, Pakistan. Elsevier Science Publishers B.V. (North-Holland) 263