LABORATORY STUDY OF SOME LIGHTNING-INDUCED EFFECTS IN THE IONOSPHERICPLASMA

Laboratory experiments have been conducted at MIT, using the student-b uilt Versatile Toroidal Facility (VTF), to investigate some ionospheri c plasma effects produced by lightning-induced whistler waves. Lower h ybrid waves, generated by the lightning-induced whistler waves, can ca use a chain of extensive plasma effects, such as the acceleration of e lectrons and ions and the spectral broadening of plasma waves. Two mec hanisms by which whistler waves generate lower hybrid waves can be imp ortant in the ionosphere. On is the simultaneous excitation of lower h ybrid waves and low-frequency mode waves by intense whistler waves. Th e other is the nonlinear mode conversion of whistler waves into lower hybrid waves in the presence of short-scale field-aligned density stri ations. The effect of lower hybrid waves on the spectra of Langmuir wa ves has been investigated. The results of VTF laboratory experiments s how that lower hybrid waves can beat with Langmuir waves to produce fr equency-upshifted and frequency-downshifted Langmuir waves, broadening the spectra of Langmuir waves. The intensity of these beat waves, how ever, depends upon the angle of wave propagation with respect to the b ackground magnetic field. (C) 1998 Elsevier Science Ltd. All rights re served.