TITLE:
Solar Activity, Solar Wind and Geomagnetic Signatures
AUTHORS:
Jean-Louis Zerbo, Frédéric Ouattara, Christine Amory Mazaudier, Jean-Pierre Legrand, John D. Richardson
KEYWORDS:
Solar Wind; Geomagnetic Activity; Solar Activity; Geomagnetic Index aa
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.3 No.4,
October
21,
2013
ABSTRACT: The present study investigates solar events through geomagnetic
activity and physical processes on the Sun: 1) Quiet activity (QA) related to
the slow solar wind, 2) Recurrent activity (RA) related to high and moderate
speed solar wind streams from coronal holes, 3) Shock activity (SA) identified
by observations of SSCs and 4) Unclear activity (UA) which contains all
activity not covered by the first three cases. For recent cycles, we analyze
and emphasize some important results: Quiet activity is predominant for cycle
23, comprising 40% of the total activity and over 80% of the activity near
solar minimum. Shock and recurrent activity contributions to total geomagnetic
activity are largest in cycle 20. The most fluctuating events are observed
during cycles 21 and 22. Throughout solar cycle 23, the contribution, from each
type of activity, differs from recent solar cycles, with larger percentages of quiet and
recurrent activity and less unclear activity. These percentages are similar to
those in solar cycles observed in the late 1800s. Since 1963, solar wind data
are available. We analyze the distribution of the solar wind velocity for each
geomagnetic class of activity and find that: 1) Within each activity type aa
does not depend on V, 2) Approximately 80% of the solar wind has V > 450 km/s for
RA, 3) SA and UA both have 60% of the solar wind V > 450 km/s. We found the
following conditions for all four solar cycles: 1) For QA 95% of
solar wind speeds are in the range 399 ± 69 km/s, 2) For RA 95% of the solar
wind speeds range from 582 ± 110 km/s, 3) For SA 95% of the solar wind
velocities are order of 482 ± 101.4 km/s, and 4) For UA 95% of solar wind
speeds are 480 ± 85.82 km/s. These results confirm the classification scheme
that QA reflects slow wind effects, RA effects high wind stream and UA answers to the
fluctuations between high wind stream (~60%) and slow wind (~40%).
The study shows that high wind stream (~60%) and slow wind (~40%) are both
registered for SA.