Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh21a1572h&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH21A-1572
Other
2164 Solar Wind Plasma, 2169 Solar Wind Sources, 7536 Solar Activity Cycle (2162), 7537 Solar And Stellar Variability (1650), 7599 General Or Miscellaneous
Scientific paper
Knowledge of the presence and evolution of periodicities in the solar wind at out--of--ecliptic latitudes can give information about the latitudinal structure of the solar wind and help distinguish between theories that predict the global characteristics of the solar wind and heliosheet. We have computed the spectrogram of the plasma velocity measured by the Ulysses spacecraft in the interval of 1991--2008 in the range of 5-- and 40--days and confirmed periodicities observed in previous limited--time--interval studies. A statistical method has been developed to determine if the observed periodicities are due to physical effects such as current sheet crossings or multiple coronal holes as opposed to being harmonics of the fundamental approximately 26--day period. Based on those criteria, we conclude that many 13--day periods are due to physical processes and not simply harmonics of the 26--day period. An example occurs in late 1999 when Ulysses was at mid- latitudes; a clear 13--day period is present without an accompanying 26--day period. The spectrogram also reveals 14--, 23--, and 30--35--day periods during solar minimum while Ulysses was at high southern latitudes. This feature appears for both solar cycles 22 and 23, although the periods are slightly shorter during the solar cycle 23 southern polar pass. We also notice complexity in the periods that appear during the solar cycle 23 maximum. All of these features are interpreted in the context of warped current sheets and other periodically appearing structures.
Henderson C. M.
Weigel Robert S.
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