How Quiet is the Quiet Magnetosphere?

Abstract:

The term “quiet magnetosphere” has been accepted as a descriptor of a magnetospheric state under small solar wind driving conditions. Observations indicate that such a state entails a substantial reduction of field-aligned currents, the polar cap potential, polar cap size, and general convection in the magnetosphere. While this paradigm is often discussed, little research has been applied to determine the detailed state of the structure of the magnetosphere. Due to basic constraints, such as entropy conservation, it appears, for example, very likely that the state of the quiet magnetosphere depends on the dynamic history. Relaxation to a unique relaxed state, should, if at all, only be possible on some yet undetermined relaxation time scale. Finally, the quiet state should depend on residual fluctuations in the solar wind driver, even if the IMF is northward. This presentation is shedding some first light on the issue of the quiet magnetosphere. We are using global MHD simulations to study the relaxation process starting from different driven states. By studying different key parameters, we derive estimates for relaxation time scales, and we will demonstrate the role solar wind fluctuations play in shaping the typical behavior of a relaxed magnetosphere.