Pressure balance across magnetic flux ropes in the ionosphere of Venus

[1] The planet Venus has a dense atmosphere, and hence an ionosphere, and does not possess an intrinsic magnetic field. The solar wind interacts directly with the atmosphere and ionosphere of Venus. The Pioneer Venus Orbiter (PVO) observed many small-scale magnetic rope-like structures within the ionosphere. We examine thermal pressure variations for 2000 ropes for a wide range of altitudes and solar zenith angles. We demonstrate that flux ropes are statistically force-free at low altitudes, meaning that a decrease of thermal pressure variation across them is not needed to compensate for the magnetic pressure in these ropes. However, at higher altitudes, there is a statistical tendency for ropes to display a thermal pressure variation across them, indicating that these ropes are not fully force-free. INDEX TERMS: 2780 Magnetospheric Physics: Solar win