It is shown that plane viscosity stratified system under longitudinal tempe
rature gradient may exhibit long-wavelength instabilities of a purely kinet
ic nature which persist at arbitrary small Reynolds number. The first insta
bility is so-called alpha effect, and the second one is a new surface-tensi
on-induced instability. The weakly nonlinear equations for the evolving int
erfaces are derived and simulated. (C) 1999 American Institute of Physics.
CS 1070-6631(99)03908-2].