Pete Riley, J. T. Gosling, D. J. McComas, NIS-1, MS D466, Los Alamos National Laboratory, Los Alamos, NM 87545, USA J. G. Luhmann (Univ. California, Space Sciences Lab., Berkeley, CA), V. J. Pizzo (NOAA/SEC, Boulder, CO), D. A. Biesecker (School of Phys. and Space Res., Univ. of Birmingham, UK), T. Hoeksema (HEPL Annex B213, Stanford, CA), A. J. Lazarus (MIT, Cambridge, MA), A. Lecinski (HAO, NCAR, Boulder, CO), L. Strachan (CfA, Cambridge, MA 02138, USA), B. Thompson (NASA GSFC/Applied Research Corp., MD, USA)
The period designated "Whole Sun Month" (WSM, August 10 - September 8, 1996) occurred serendipitously with the return of solar wind variability at the Ulysses spacecraft. Ulysses was located between N29 deg. and N27 deg. heliographic latitude, 4.2 and 4.3AU, and on the opposite side of the Sun from Earth. For more than a year prior to July, 1996, Ulysses had been immersed exclusively in high-speed coronal-hole flow. Since then, Ulysses has observed a regular pattern of alternating fast/slow streams that are typical near the minimum of the solar activity cycle. In this study, we explore the evolution of the solar wind between the Sun and Ulysses during an interval surrounding WSM. In view of Ulysses' position relative to Earth, we extend the interval of analysis so as to include several solar rotations both before and after WSM. In addition, this interval includes an evolving equatorward extension of the coronal hole (the so-called "elephant's trunk") and an equatorial active region near ~250 deg. Carrington longitude that appears to significantly modify the topology of the streamer belt. We approach our study in two ways. First, using a fluid dynamic code, we model the evolution of the stream structure out to the location of Ulysses by specifying the speed, density, and temperature at the solar source surface. Solar source surface potential field models from the Wilcox Solar Observatory are used to define the boundary conditions on the velocity gradients with respect to the heliospheric current sheet. Comparison of these results with Ulysses (as well as near-Earth) observations, allows us to assess the quality of the inner (source surface) boundary conditions of the model. And second, using several techniques, we map the measured in situ plasma measurements at Ulysses back to the Sun and compare with SOHO observations enabling us to associate solar-wind structures with structures at the Sun. This may also allow us to identify a latitude range from which the flow at Ulysses originates.
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