Effects of Different Geomagnetic Storm Drivers on the Ring Current: CRCM Results

The storm-time magnetic disturbance at the Earth\u27s equator, as commonly measured by the Dst index, is induced by currents in the near-Earth magnetosphere. The ring current is generally considered the most important contributor, but other magnetospheric currents have also been found to have significant effects. Of the two main types of solar geomagnetic storm drivers, Coronal Mass Ejections (CMEs) tend to have a much greater impact on Dst than Corotating Interaction Regions (CIRs). Ring current models have been found to underestimate Dst, particularly during storms driven by CIRs. One possible explanation is that the models neglect to handle some aspect of ring current physics that is particularly important for CIRs. This study uses the Comprehensive Ring Current Model (CRCM) to estimate the ring current contribution to Dst for a selection of storms of various strengths and different drivers (CMEs and CIRs) that have solar wind parameters that fit a typical profile. The model boundary is set to 10 RE at the equator, encompassing the entire ring current region. The magnetic field is held fixed, based on average storm parameters, which limits our model results to the effects of convection and plasma sheet density at the model boundary. Our model results generally show good agreement with the size and timing of fluctuations in Dst, which indicates that convection and boundary conditions play an important role in shaping Dst. We also find excellent agreement with the magnitude of Dst for CME-driven storms. For CIR-drivenstorms, however, the magnitude at the peak of the storm frequently deviates from actual Dst. In general, we agree with the results of previous research that CIR-driven storms are more underpredicted. However, this study includes some weaker CIR-driven stormsfor which Dst is actually overpredicted. Overall, when examining the dependence of modeled Dst* on actual Dst* at storm peak, we find that there is a statistically significant difference between CME- and CIR-driven storms. We also find that approximately half of the total ring current energy lies beyond an L-value of 6.6. However, this figure could be overestimated due to the use of a static magnetic field, which limits radial transport. Key Points Modeled vs actual Dst at storm peak is significantly different for CMEs and CIRs Convection and plasma sheet density are important for ring current energization Model shows half of total ring current energy lies beyond an L-value of 6.6

Mathematical models for vulnerable plaques

A plaque is an accumulation and swelling in the artery walls and typically consists of cells, cell debris, lipids, calcium deposits and fibrous connective tissue. A person is likely to have many plaques inside his/her body even if they are healthy. However plaques may become "vulnerable", "high-risk" or "thrombosis-prone" if the person engages in a high-fat diet and does not exercise regularly. In this study group, we proposed two mathematical models to describe plaque growth and rupture. The first model is a mechanical one that approximately treats the plaque as an inflating elastic balloon. In this model, the pressure inside the core increases and then decreases suggesting that plaque stabilization and prevention of rupture is possible. The second model is a biochemical one that focuses on the role of MMPs in degrading the fibrous plaque cap. The cap stress, MMP concentration, plaque volume and cap thickness are coupled together in a system of phenomenological equations. The equations always predict an eventual rupture since the volume, stresses and MMP concentrations generally grow without bound. The main weakness of the model is that many of the important parameters that control the behavior of the plaque are unknown. The two simple models suggested by this group could serve as a springboard for more realistic theoretical studies. But most importantly, we hope they will motivate more experimental work to quantify some of the important mechanical and biochemical properties of vulnerable plaques

Self-Consistent Model of Magnetospheric Electric Field, Ring Current, Plasmasphere, and Electromagnetic Ion Cyclotron Waves: Initial Results

Further development of our self-consistent model of interacting ring current (RC) ions and electromagnetic ion cyclotron (EMIC) waves is presented. This model incorporates large scale magnetosphere-ionosphere coupling and treats self-consistently not only EMIC waves and RC ions, but also the magnetospheric electric field, RC, and plasmasphere. Initial simulations indicate that the region beyond geostationary orbit should be included in the simulation of the magnetosphere-ionosphere coupling. Additionally, a self-consistent description, based on first principles, of the ionospheric conductance is required. These initial simulations further show that in order to model the EMIC wave distribution and wave spectral properties accurately, the plasmasphere should also be simulated self-consistently, since its fine structure requires as much care as that of the RC. Finally, an effect of the finite time needed to reestablish a new potential pattern throughout the ionosphere and to communicate between the ionosphere and the equatorial magnetosphere cannot be ignored

Anisotropic diffusion in continuum relaxation of stepped crystal surfaces

We study the continuum limit in 2+1 dimensions of nanoscale anisotropic diffusion processes on crystal surfaces relaxing to become flat below roughening. Our main result is a continuum law for the surface flux in terms of a new continuum-scale tensor mobility. The starting point is the Burton, Cabrera and Frank (BCF) theory, which offers a discrete scheme for atomic steps whose motion drives surface evolution. Our derivation is based on the separation of local space variables into fast and slow. The model includes: (i) anisotropic diffusion of adsorbed atoms (adatoms) on terraces separating steps; (ii) diffusion of atoms along step edges; and (iii) attachment-detachment of atoms at step edges. We derive a parabolic fourth-order, fully nonlinear partial differential equation (PDE) for the continuum surface height profile. An ingredient of this PDE is the surface mobility for the adatom flux, which is a nontrivial extension of the tensor mobility for isotropic terrace diffusion derived previously by Margetis and Kohn. Approximate, separable solutions of the PDE are discussed.Comment: 14 pages, 1 figur

Global, collisional model of high‐energy photoelectrons

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95539/1/grl8976.pd

Continued convection and the initial recovery of Dst

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94856/1/grl16086.pd

A new solar windâ driven global dynamic plasmapause model: 2. Model and validation

A new solar windâ driven global dynamic plasmapause (NSWâ GDP) model has been constructed based on the largest currently available database containing 49,119 plasmapause crossing locations and 3957 plasmapause profiles (corresponding to 48,899 plasmapause locations), from 18 satellites during 1977â 2015 covering four solar cycles. This model is compiled by the Levenbergâ Marquardt method for nonlinear multiparameter fitting and parameterized by VSW, BZ, SYMâ H, and AE. Continuous and smooth magnetic local time dependence controlled mainly by the solar windâ driven convection electric field ESW is also embedded in this model. Compared with previous empirical models based on our database, this new model improves the forecasting accuracy and capability for the global plasmapause. The diurnal, seasonal, and solar cycle variations of the plasmapause can be captured by the new model. The NSWâ GDP model can potentially be used to forecast the global plasmapause shape with upstream solar wind and interplanetary magnetic field parameters and corresponding predicted values of SYMâ H and AE and can also be used as input parameters for other inner magnetospheric coupling models, such as dynamic radiation belt and ring current models and even MHD models.Key PointsA new solar windâ driven global dynamic plasmapause model based on multisatellite observations is constructedThis model is parameterized by VSW, interplanetary magnetic field BZ, SYMâ H, and AE and has continuous and smooth MLT dependenceThis model is potentially applicable to inner magnetospheric research studies and space weather forecastsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138428/1/jgra53619.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138428/2/jgra53619_am.pd

A new solar windâ driven global dynamic plasmapause model: 1. Database and statistics

A large database, possibly the largest plasmapause location database, with 49,119 plasmapause crossing events from the in situ observations and 3957 plasmapause profiles (corresponding to 48,899 plasmapause locations in 1 h magnetic local time (MLT) intervals) from optical remote sensing from 1977 to 2015 by 18 satellites is compiled. The responses of the global plasmapause to solar wind and geomagnetic changes and the diurnal, seasonal, solar cycle variations of the plasmapause are investigated based on this database. It is found that the plasmapause shrinks toward the Earth globally and a clear bulge appears in the afternoon to premidnight MLT sector as the solar wind or geomagnetic conditions change from quiet to disturbed. The bulge is clearer during storm times or southward interplanetary magnetic field. The diurnal variations of the plasmapause are most probably the result of the difference between the magnetic dipole tilt and the Earth’s spin axis. The seasonal variations of the plasmapause are characterized by equinox valleys and solstice peaks. It is also found that the plasmapause approaches the Earth during high solar activity and expands outward during low solar activity. This database will help us study and understand the evolution properties of the plasmapause shape and the interaction processes of the plasmasphere, the ring current, and the radiation belts in the magnetosphere.Key PointsThe largest currently available plasmapause location database is compiled based on observations from 18 satellites from 1977 to 2015This database reveals the responses of the global plasmapause locations to solar wind and geomagnetic changesThe plasmapause locations exhibit clear MLTâ dependent diurnal, seasonal, and solar cycle variationsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138358/1/jgra53617_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138358/2/jgra53617.pd