  Genesis of flux ropes observed by Pioneer-Venus Orbiter in the
photoequilibrium region at Venus is analysed. Stability analysis of the
large-scale magnetic field pushed deep inside during period of high dynamic
pressure of solar wind had shown that the top-side boundary of the magnetic
belt located within the region of photoequilibrium is unstable. The finite
conductivity of plasma tends to stabilise the instability so that the
bottom-side part of the magnetic belt is regular. Non-numerous flux ropes which
were observed above the predicted instability region are likely moving upward
because of the magnetic buoyancy.
