Periodic plasma escape from the mass-loaded Kronian magnetosphere

Abstract

We use a single-fluid global MHD model to study the solar wind control of large-scale mass loading and plasma release phenomena in the Kronian magnetosphere. We show that, at high solar wind dynamic pressure, the loss of plasma in the magnetotail is continuous. At medium dynamic pressure, plasmoids are pinched off periodically along an X-line in the postmidnight sector through a cascade of helical reconnection. Plasmoids have a magnetic topology of a helical flux rope with its ends anchoring in the polar regions of Saturn. With decreasing dynamic pressure, the repetition period of plasmoids gradually increases. A higher mass-loading rate or a higher axial tilt of Saturn makes the repetition period longer. At low dynamic pressure, the release of plasmoids becomes quasi-periodic or chaotic. The pressure control of the repetition period is very similar to the behavior of a dripping faucet. The mass and volume of the closed magnetosphere are smaller at lower dynamic pressures because of a relatively longer X-line. In our simulations, large-scale plasmoids are responsible for less than 8% of the total mass loss, and the rest of the plasma is lost via cross-field diffusion or other small-scale mechanisms. Copyright 2010 by the American Geophysical Union.