scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Evolution of 3D solar wind structure during cycles 22 and 23
Tokumaru Munetoshi , Fujiki Ken'ichi , Msasyoshi Kojima
Solar-Terrestrial Environment Laboratory, Nagoya University
Interplanetary scintillation (IPS) measurements made with the 327-MHz multi-station system
of the Solar-Terrestrial Environment Laboratory of Nagoya University were analyzed to study
long-term variation of the global solar wind structure during cycles 22 and 23 (1985-2008). In
this analysis, the computer-assisted tomography method was applied to retrieve threedimensional
distribution of the solar wind speed from IPS observations. The result clearly
demonstrated that the solar wind structure evolved drastically with the solar cycle; the source
surface areas of fast (slow) wind increased systematically as the solar activity declines,
reaching the maximum (minimum) value at the minimum phase. In addition, the spatial
distribution of fast and slow winds showed different latitude preference. High latitude regions
were mostly dominated by the fast wind except for a few years around the maximum phase,
while low latitude regions were occupied with the slow wind throughout the cycle. These
behaviors of fast/slow winds are regarded as manifestation of the solar cycle change of Sun's
magnetic field. An excellent correlation between fast/slow wind areas and polar magnetic
field is demonstrated here. The important point to note is that the solar wind speed
distribution for the current minimum significantly differs from that for the previous minimum.
This difference is considered as a consequence of weaker polar fields in the current minimum,
and may be a part of secular variation of the solar activity.