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Session 19 - The Sun.
Oral session, Monday, June 08
In a recent paper Leinert and Jackson (1998) analyzed brightness observations from the Helios spacecraft photometers, in situ data and interplanetary scintillation (IPS) velocities, and used these to model global heliospheric plasma changes over solar cycle no. 21. Our analysis shows changes in the solar wind flow in terms of mass and velocity over one Carrington rotation. We model the available IPS velocity observations using a tomographic least squares fit to determine solar wind speeds. This technique, crucial to our analysis, provides more contrast between high speed winds over the solar poles and low speed winds near the equator than possible with previous techniques. Here, we confirm the validity of this technique with recent Ulysses spacecraft measurements and a comparison between Ulysses-measured solar wind speeds and IPS velocities available from the STELab in Japan.
The primary result of the measurements over solar cycle 21 show the extent to which the approximation of constant solar wind momentum flux is valid in more detail than was previously possible. Under this assumption we find that additional mass at about the 15% level is added to the solar wind at solar activity maximum, and that this mass is most likely present in the form of discrete events (Coronal Mass Ejections). This implies that there are probably two different processes acting to remove solar wind from the sun - one provided by a constant coronal energization, and one that is associated with the strongest solar magnetic fields.
Leinert, Ch. and B.V. Jackson, Global Solar Wind Changes Over Solar Cycle 21: a Combination of Helios Photometer, In-situ and IPS Data, Astrophys. J., (accepted), 1998.
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