Genesis of Flux Ropes Observed by Pioneer-Venus Orbiter in the Photoequilibrium Region At Venus

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.