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ACE News #94 - Dec 16, 2005
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We announce the availability of an enhanced and extended dataset for the study of solar wind heavy-ion composition and dynamics. These data come from measurements by the Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ion Mass Spectrometer (SWIMS) on ACE. The data are obtained from energy and time-of-flight measurements via an inversion method that, to a large degree, removes the overlap between neighboring ions. The resulting dataset establishes a new standard in mass and charge resolution for in-situ heavy-ion measurements.
The attached figure is intended to demonstrate the diagnostic power of the newly released SWICS datasets. The insert shows six days of SWICS data in mid-April 2002, which included some of the most intense geomagnetic disturbances of the solar cycle. The top-panel shows average charge states of Fe, C, and O; the mid-panel shows elemental abundances of He, C, and Fe, all relative to O; the bottom panel shows speeds of Fe, O, C and He with the same color scale as above. The speeds of the heavy ions show clear signatures for the arrival of shocks (S), driven by coronal mass ejections. The ionic charge states in the top panel indicate the arrival of CME plasma (C), through the occurrence of unusual ionic charge states for Fe, C, and O. The middle panel shows elemental abundances indicative of the physical conditions of the source regions from which the CMEs originated. Shock boundaries and leading-edge CME boundaries are shown as yellow and orange lines, respectively.
The first CME, arriving before April 19th, shows a classical CME with a single shock, as sketched in the background of the figure. The second CME, arriving after April 19th, has a shock driven into the first ejection, showing heliospheric interactions of two CMEs. The final perturbation after April 21 only exhibits a shock, but no CME plasma, indicating a glancing blow away from the CME, but interacting with the CME associated shock.
This is a small subset of the delivered SWICS data, with unprecedented potential to address the origin of CMEs (through elemental composition), their thermodynamic expansion through the heliosphere (through ionic charge states and temperatures), and their dynamic interaction in the heliosphere (through ion-specific speeds and temperatures).
This new solar wind data set may be found at the ACE Science Center Level 2 Data web page.
Submitted by Jim M. Raines, Susan T. Lepri, Thomas H. Zurbuchen, George Gloeckler, and L. A. Fisk of the University of Michigan. Please direct questions or comments to firstname.lastname@example.org.
Last modified 16 Dec 2005, by