Dusan Odstrcil

Modeling 3-D solar wind structure

Abstract Recent advances in numerical methods and computer systems make it possible to tackle complicated, more realistic ambient and transient solar wind flows. An overview of the ongoing work performed at the NOAA Space Environment Center is presented with examples illustrating: (a) global.3-D interaction of a CME propagating in structured background solar wind, (b) incorporation of a more realistic ambient solar wind, (c) merging of coronal and heliospheric models to track CMEs, and (d) near-Earth solar wind simulations. The aim is to highlight the complexities confronting numerical modelers in meeting challenges imposed by space weather research and forecasting.

Flux cancellation and coronal mass ejections

Time dependent magnetohydrodynamic computations of the flux cancellation mechanism are presented. Previous authors have discussed this mechanism as a possible cause for the formation of prominences and the trigger for prominence eruptions and coronal mass ejections (CMEs). This paper shows that flux cancellation in an energized two-and-one-half-dimensional helmet streamer configuration first leads to the formation of stable flux rope structures. When a critical threshold of flux reduction is exceeded, the configuration erupts violently. Significant amounts of stored magnetic energy are released through magnetic reconnection. The ejected flux rope propagates out into the solar wind and forms an interplanetary shock wave. A similar eruption occurs for a three-dimensional calculation where the ends of the flux rope field lines are anchored to the Sun. The flux cancellation mechanism unifies the processes of prominence formation, prominence eruption, and CME initiation, and thus provides an attractive hypothesis for explaining the cause of these dynamic events.Time dependent magnetohydrodynamic computations of the flux cancellation mechanism are presented. Previous authors have discussed this mechanism as a possible cause for the formation of prominences and the trigger for prominence eruptions and coronal mass ejections (CMEs). This paper shows that flux cancellation in an energized two-and-one-half-dimensional helmet streamer configuration first leads to the formation of stable flux rope structures. When a critical threshold of flux reduction is exceeded, the configuration erupts violently. Significant amounts of stored magnetic energy are released through magnetic reconnection. The ejected flux rope propagates out into the solar wind and forms an interplanetary shock wave. A similar eruption occurs for a three-dimensional calculation where the ends of the flux rope field lines are anchored to the Sun. The flux cancellation mechanism unifies the processes of prominence formation, prominence eruption, and CME initiation, and thus provides an attractive hypothe...

Numerical Simulation of Interacting Magnetic Flux Ropes

A 212‐D MHD numerical model is used to investigate the dynamic interaction between two flux ropes (clouds) in a homogeneous magnetized plasma. One cloud is set into motion while the other is initially at rest. The moving cloud generates a shock which interacts with the second cloud. Two cases with different characteristic speeds within the second cloud are presented. The shock front is significantly distorted when it propagates faster (slower) in the cloud with larger (smaller) characteristic speed. Correspondingly, the density behind the shock front becomes smaller (larger). Later, the clouds approach each other and by a momentum exchange they come to a common speed. The oppositely directed magnetic fields are pushed together, a driven magnetic reconnection takes a place, and the two flux ropes gradually coalescence into a single flux rope.

Magnetohydrodynamic modeling of interplanetary CMEs

Heliospheric models of coronal mass ejection (CME) propagation and evolution provide an important insight into the dynamics of CMEs and are a valuable tool for interpretating interplanetary in situ observations. Moreover, they represent a virtual laboratory for exploring conditions and regions of space that are not conveniently or currently accessible by spacecraft. We summarize our recent advances in modeling the properties and evolution of CMEs in the solar wind. We describe our current state of research with three examples: 1) interpreting the global context of in situ observations; 2) identifying new phenomena in the simulations; and 3) computing geoeffective phenomena. We conclude by discussing what topics will likely be important for models to address in the future.

Ensemble modeling of successive halo CMEs observed during 2-4 Aug 2011

Previously, we investigated the sensitivity of the 3D MHD Wang-Sheeley-Arge (WSA)-Enlil numerical results to the input “cone” geometry for an Earth-directed “halo” coronal mass ejection (CME) event [1]. A modeling ensemble was created from multiple sets of input parameters obtained through the use of the cone fitting tool together with realistic ranges for the angular width and leading edge distance estimated from STEREO limb observations. We obtained a spread of ~ 13 hours in the ensemble shock arrival times, which overlapped and was nearly centered on the observed arrival time. Because the sensitivity of the modeling ensemble may be event-dependent, we conduct an ensemble modeling study for three consecutive halo CME events. These events were selected in part because of the availability of STEREO limb observations, which help to constrain the initial CME geometries during the cone fitting process, but also because of the opportunity to explore the predictive capability of WSA-Enlil-cone in modeling mult...