CONVECTIVE TURBULENCE IN WEAKLY IONIZED PLASMA

We show that the two-dimensional E x B and Rayleigh-Taylor driven turb ulence in the weakly ionized plasma of the Earth's ionosphere is isomo rphic to the viscous convection of an ordinary fluid in a porous mediu m due to temperature gradients (E is the ambient electric field and B is the magnetic field). The turbulence results in fluctuations of the electron density which have been observed for several decades by incoh erent radar backscattering techniques and rocket mounted instruments. A two-dimensional single field equation has been derived to describe t his convective turbulence. Numerical simulations of this equation reve al a strong anisotropy in the turbulence, which consists of rising hot bubbles and falling cool bubbles, These bubbles break up into fingers . Sharp gradients are generated in the direction perpendicular to grav ity or equivalently the driving electric field E. After reaching a qua sisteady state, the omnidirectional energy spectrum approaches k(-2). Physical mechanisms leading to anisotropy are analysed. An equation, a nalogous to that for the convective ionospheric plasma, but applicable instead to the two-dimensional convection in the Earth's mantle is de rived and simulated. The results from this simulation are discussed.