Transition to Continuous Unloading: Differentiating Storms and Substorms in211 Magnetospheric Dynamics

摘要

We present a new physical model for the global energy flows in the magnetotail211u001ewhich implies a distinction in the driving of storms and substorms. Using a model 211u001esystem, we demonstrate that some properties of both storms and substorms can be 211u001eobtained from the same dynamical system for different levels of solar wind 211u001eforcing. To say that storms are made up of substorms would be incorrect. Instead 211u001ewe see that quasiperiodic substorms result for weak forcing, while a steady storm 211u001eensues for strong forcing, with a continuous transition between the two. There is 211u001ean inverse bifurcation from unstable to stable in the state of the system with 211u001erespect to increasing driving. (Topologically, an attractor of dimension one for 211u001eweak forcing becomes an attractor of dimension zero for strong forcing). The 211u001eproperties of both states are analyzed for their energy contents and the power 211u001eflows between energy components. These states relate to two types of unloading of 211u001etail flux: storage-unloading and continuous unloading. The rapid storage-211u001eunloading process is shown to be equivalent to the substorm expansion onset. The 211u001ehypothesis is advanced that a magnetic storm is represented by the state of 211u001enearly continuous unloading.