  In this work we consider the effect of a small-scale helical driving force on
fluid with a stable temperature gradient with Reynolds number Re<<1. At first
glance, this system does not appear to have any instability. However, we show
that large-scale vortex instability appears in fluid despite its stable
stratification. In the non-linear mode, this instability gets saturated and
gives a large number of stationary spiral vortex structures. Among these
structures there is a stationary helical soliton and a kink of a new type. The
theory is built on the rigorous asymptotical method of multi-scale development.
