Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh31c2021l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH31C-2021
Astronomy and Astrophysics
Astrophysics
[7513] Solar Physics, Astrophysics, And Astronomy / Coronal Mass Ejections, [7924] Space Weather / Forecasting, [7959] Space Weather / Models
Scientific paper
As we progress toward the next solar maximum, we have a unique opportunity to use multi-perspective spacecraft observations together with numerical models to better understand the evolution and propagation of coronal mass ejections (CMEs). Of interest to both the scientific and forecasting communities are the Earth-directed "halo" CMEs, since they typically produce the most geoeffective events. To accurately model a CME, its initial speed, size, and propagation orientation are measured from white light coronagraph observations obtained at L1 along the Sun-Earth line. However, it is well known that determining the actual initial geometries of halo CMEs is a challenge due to the plane-of-sky projection effects. We select for our study the recent 15 February 2011 halo CME event. During this time the STEREO-A and -B spacecraft were fortuitously located ~90 degrees away from the Sun-Earth line such that the CME was viewed as solar limb events from these two spacecraft, thereby providing a more reliable constraint on the initial CME geometry. Together with these multi-perspective observations, we use a simple geometrical description that assumes a cone shape for a CME to calculate its angular width and central position. We then simulate the event using the coupled Wang-Sheeley-Arge (WSA)/Enlil 3D numerical solar corona-solar wind model. To drive the background solar wind we use daily updated global photospheric magnetic field maps (magnetograms) from the Global Oscillation Network Group (GONG). A more global perspective of the propagation and evolution of the CME is obtained from the simulation results than that provided by only using spacecraft observations located at fixed vantage points. To improve our modeling techniques, we assess the sensitivity of the modeled CME arrival times to the initial input CME geometry by creating an ensemble of numerical simulations based on multiple sets of cone parameters for this event. We find that the accuracy of the modeled arrival times not only depends on the initial input CME geometry, but also on the accuracy of the modeled solar wind background, which is driven by the input magnetograms. Thus to improve our modeling of the background solar wind, we use the recently developed data-assimilated magnetograms produced by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model, which provide a more instantaneous snapshot of the global photospheric field distribution than that provided by traditional daily updated magnetograms. We present our modeling results in conjunction with observations of the CME and discuss the performance of the cone+WSA/Enlil model in reproducing the global properties of the event.
Arge Charles Nickolos
Lee Chong OH
Millward George H.
Odstrcil Dusan
Pizzo Victor J.
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