Understanding storm-time ring current sources: Data analysis and global modeling.

With the availability of abundant, high-quality recent observations (ground-based and space-borne) and the newly-developed Space Weather Modeling Framework (SWMF), the storm-time ring current sources are examined via extensive data analyses and global storm simulations. The results of this dissertation work improve our understanding of upstream solar wind conditions, immediate plasma-sheet sources, and ionospheric outflow effect during storms. It is found in the magnetic cloud-storm study that ∼76% of magnetic clouds cause storms, but only ∼30% of storms are caused by clouds. A storm can be driven by a cloud's leading field, axial field, trailing field, or the combination thereof. It is shown that the leading field is the most geoeffective region and the sheath is equally effective at causing storms during solar maximum compared to solar minimum. A new name, quasicloud, is proposed for those cloud-like solar wind structures. Superposed epoch analyses are performed to make comparisons of typical behaviors of upstream solar wind plasma and interplanetary magnetic field (IMF), geosynchronous-orbit hot ions, and geomagnetic indices in four storm categories: moderate and in tense storms at solar minimum and maximum. The long-known control of geomagnetic activity mainly by southward IMF Bz is supported in the investigations. The averaged interplanetary causes of intense storms at solar minimum are against the well-known empirical criteria (Bz ≤ -10 nT for ≥ 3 hrs). Around storm minimum in each category, hot ions at geosynchronous orbit are denser near dawn than dusk. In the second part of the dissertation work, high-performance storm simulations are performed with the actual and superposed solar wind as input to the SWMF, respectively. It is shown that the SWMF is reaching a sophistication level for allowing quantitative comparison with observations. Major storm characteristics except for the recovery phase are successfully reproduced. It is demonstrated that ionospheric outflow plays an important role in causing a storm. IMF Bz ≤ -5 nT for ≥ 2 hrs without large oscillations in the solar wind and an increased inner boundary mass density to compensate is not geoeffective enough to cause a moderate storm. 24 M virtual geostationary satellites are introduced to make data-model comparisons straightforward.Ph.D.Atmospheric sciencesEarth SciencesGeophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125936/2/3224794.pd