The August 24, 2002 Coronal Mass Ejection: When a Western Limb Event Connects to Earth

We discuss how some coronal mass ejections (CMEs) originating from the western limb of the Sun are associated with space weather effects such as solar energetic particles (SEPs), shock or geo-effective ejecta at Earth. We focus on the August 24, 2002 coronal mass ejection, a fast (~ 2000 km/s) eruption originating from W81. Using a three-dimensional magneto-hydrodynamic simulation of this ejection with the Space Weather Modeling Framework (SWMF), we show how a realistic initiation mechanism enables us to study the deflection of the CME in the corona and the heliosphere. Reconnection of the erupting magnetic field with that of neighboring streamers and active regions modify the solar connectivity of the field lines connecting to Earth and can also partly explain the deflection of the eruption during the first tens of minutes. Comparing the results at 1 AU of our simulation with observations by the ACE spacecraft, we find that the simulated shock does not reach Earth, but has a maximum angular span of about 120$^\circ$, and reaches 35$^\circ$ West of Earth in 58 hours. We find no significant deflection of the CME and its associated shock wave in the heliosphere, and we discuss the consequences for the shock angular span.Comment: 7 pages, 4 figures, IAU 257 Symposium Proceeding

Towards a Realistic, Data-Driven Thermodynamic MHD Model of the Global Solar Corona

In this work we describe our implementation of a thermodynamic energy equation into the global corona model of the Space Weather Modeling Framework (SWMF), and its development into the new Lower Corona (LC) model. This work includes the integration of the additional energy transport terms of coronal heating, electron heat conduction, and optically thin radiative cooling into the governing magnetohydrodynamic (MHD) energy equation. We examine two different boundary conditions using this model; one set in the upper transition region (the Radiative Energy Balance model), as well as a uniform chromospheric condition where the transition region can be modeled in its entirety. Via observation synthesis from model results and the subsequent comparison to full sun extreme ultraviolet (EUV) and soft X-Ray observations of Carrington Rotation (CR) 1913 centered on Aug 27, 1996, we demonstrate the need for these additional considerations when using global MHD models to describe the unique conditions in the low corona. Through multiple simulations we examine ability of the LC model to asses and discriminate between coronal heating models, and find that a relative simple empirical heating model is adequate in reproducing structures observed in the low corona. We show that the interplay between coronal heating and electron heat conduction provides significant feedback onto the 3D magnetic topology in the low corona as compared to a potential field extrapolation, and that this feedback is largely dependent on the amount of mechanical energy introduced into the corona.Comment: 17 pages, 11 figures, Submitted to ApJ on 12/08/200

Numerical Studies of the Solar Energetic Particle Transport and Acceleration

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76215/1/AIAA-2005-4928-462.pd

Numerical Investigations of Catastrophe in Coronal Magnetic Configuration Triggered by Newly Emerging Flux

We performed 2D magnetohydrodynamical numerical experiments to study the response of the coronal magnetic configuration to the newly emerging magnetic flux. The configuration includes an electric-current-carrying flux rope modeling the prominence floating in the corona and the background magnetic field produced by two separated magnetic dipoles embedded in the photosphere. Parameters for one dipole are fixed in space and time to model the quiet background, and those for another one are time dependent to model the new flux. These numerical experiments duplicate important results of the analytic solution but also reveal new results. Unlike previous works, the configuration here possesses no symmetry, and the flux rope could move in any direction. The non-force-free environment causes the deviation of the flux rope equilibrium in the experiments from that determined in the analytic solution. As the flux rope radius decreases, the equilibrium could be found, and it evolves quasi-statically until the flux rope reaches the critical location at which the catastrophe occurs. As the radius increases, no equilibrium exists at all. During the catastrophe, two current sheets form in different ways. One forms as the surrounding closed magnetic field is stretched by the catastrophe, and another one forms as the flux rope squeezes the magnetic field nearby. Although reconnection happens in both the current sheets, it erases the first one quickly and enhances the second simultaneously. These results indicate the occurrence of the catastrophe in asymmetric and non-force-free environment, and the non-radial motion of the flux rope following the catastrophe

Modeling a space weather event from the Sun to the Earth: CME generation and interplanetary propagation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94980/1/jgra17180.pd

A Three-dimensional Model of the Solar Wind Incorporating Solar Magnetogram Observations

We present a new compressible MHD model for simulating the three-dimensional structure of the solar wind under steady state conditions. The initial potential magnetic field is reconstructed throughout the computational volume using the source surface method, in which the necessary boundary conditions for the field are provided by solar magnetogram data. The solar wind in our simulations is powered by the energy interchange between the plasma and large-scale MHD turbulence, assuming that the additional energy is stored in the "turbulent" internal degrees of freedom. In order to reproduce the observed bimodal structure of the solar wind, the thermodynamic quantities for the initial state are varied with the heliographic latitude and longitude depending on the strength of the radial magnetic field

Halloween Storm Simulations with the Space Weather Modeling Framework

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77046/1/AIAA-2006-87-256.pd

Theoretical modeling for the stereo mission

We summarize the theory and modeling efforts for the STEREO mission, which will be used to interpret the data of both the remote-sensing (SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The modeling includes the coronal plasma, in both open and closed magnetic structures, and the solar wind and its expansion outwards from the Sun, which defines the heliosphere. Particular emphasis is given to modeling of dynamic phenomena associated with the initiation and propagation of coronal mass ejections (CMEs). The modeling of the CME initiation includes magnetic shearing, kink instability, filament eruption, and magnetic reconnection in the flaring lower corona. The modeling of CME propagation entails interplanetary shocks, interplanetary particle beams, solar energetic particles (SEPs), geoeffective connections, and space weather. This review describes mostly existing models of groups that have committed their work to the STEREO mission, but is by no means exhaustive or comprehensive regarding alternative theoretical approaches

Review of solar energetic particle models

Solar Energetic Particle (SEP) events are interesting from a scientific perspective as they are the product of a broad set of physical processes from the corona out through the extent of the heliosphere, and provide insight into processes of particle acceleration and transport that are widely applicable in astrophysics. From the operations perspective, SEP events pose a radiation hazard for aviation, electronics in space, and human space exploration, in particular for missions outside of the Earth’s protective magnetosphere including to the Moon and Mars. Thus, it is critical to improve the scientific understanding of SEP events and use this understanding to develop and improve SEP forecasting capabilities to support operations. Many SEP models exist or are in development using a wide variety of approaches and with differing goals. These include computationally intensive physics-based models, fast and light empirical models, machine learning-based models, and mixed-model approaches. The aim of this paper is to summarize all of the SEP models currently developed in the scientific community, including a description of model approach, inputs and outputs, free parameters, and any published validations or comparisons with data.</p