In this paper, we have discussed the possibility of excitation of zero-frequency modes by a finite-amplitude electron-sound wave in a highly non-isothermal (Ti ≫ Te) magnetoplasma. According to our investigation, the modulational instabilities of the electron-acoustic waves may produce enhanced twodimensional vortices (convection cells) and magnetic field fluctuation. Both of them can, in turn, modify transport properties of a hot magnetoplasma.

Our results could be applicable to plasmas in the earth's magnetotail (Frank, Ackerson & Lepping 1976) or thetapinches, both of which have Ti≫Te. However, for thetapinch application, one should actually modify our results to include plasma non-uniformities. In such a situation, instead of electron-acoustic waves, one encounters ion drift waves (e.g. Shukla, Yu & Varma 1981) whose modulational instabilities can readily be studied following the procedure discussed here.

Owing to the lack of experimental data, we cannot at present verify predictions of our theory for plasmas either in space or in a laboratory. However, a typical example shows that the growth rates of both the convection cells and the magnetostatic modes are quite substantial. Hence, the phenomena discussed here may indeed appear in nature.

We are grateful to Ming Yu for many useful discussions. The work of one of us(P. K. S.) was performed under the auspices of the Sonderforschungsbereich Plasmaphysik Bochum/J ülich. One of us (H.U.R.) thanks the Deutsche Akademische Austauschdienst for the award of a fellowship.