How a magnetic helix can develop at solstice in a Uranus-type rotating magnetosphere

<p class="p1">The characteristic relaxation time of the Uranus magnetosphere is of the order &#160;of the planet's rotation period. This is also the case for Jupiter or Saturn. However, the specificity of Uranus (and to a lesser extent of &#160;Neptune) is that the rotation axis and the magnetic dipole axis are separated by &#160;a large angle (~60&#176;) the consequence of which is the development of a highly dynamic and complex magnetospheric tail. In addition, and contrary to all other planets of the solar system, the rotation axis of Uranus happens to be quasi-parallel to the ecliptic plane which also implies a strong variability of the magnetospheric structure as a function of the season. The magnetosphere of Uranus is thus a particularly challenging case for global plasma simulations, even in the frame of MHD. We present a detailed analysis of MHD simulations of a fast-rotating magnetosphere inspired from Uranus at solstice. At first, a simplified case allows us to explain in detail the formation and the internal structure of a double helix that develops in the magnetotail at solstice. Then we analyse a "real" Uranus simulation with&#160;parameters for the solar wind and planetary magnetic field defined from the measurements of Voyager II flyby in 1986.</p>