252 research outputs found
Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities
We investigate the relationship between the monthly averaged maximal speeds
of coronal mass ejections (CMEs), international sunspot number (ISSN), and the
geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar
cycle 23). Our new findings are as follows. (1) There is a noteworthy
relationship between monthly averaged maximum CME speeds and sunspot numbers,
Ap and Dst indices. Various peculiarities in the monthly Dst index are
correlated better with the fine structures in the CME speed profile than that
in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not
exhibit a double peak maximum. Instead, the CME speed profile peaks during the
declining phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3) The CME
number shows a double peak similar to that seen in the sunspot numbers. The CME
occurrence rate remained very high even near the minimum of the solar cycle 23,
when both the sunspot number and the CME average maximum speed were reaching
their minimum values. (4) A well-defined peak of the Ap index between 2002 May
and 2004 August was co-temporal with the excess of the mid-latitude coronal
holes during solar cycle 23. The above findings suggest that the CME speed
index may be a useful indicator of both solar and geomagnetic activities. It
may have advantages over the sunspot numbers, because it better reflects the
intensity of Earth-directed solar eruptions
Low-Latitude Coronal Holes at the Minimum of the 23rd Solar Cycle
Low and mid-latitude coronal holes (CHs) observed on the Sun during the
current solar activity minimum (from September 21, 2006, Carrington rotation
(CR) 2048, until June 26, 2009 (CR 2084)) were analyzed using {\it SOHO}/EIT
and STEREO-A SECCHI EUVI data. From both the observations and Potential Field
Source Surface (PFSS) modeling, we find that the area occupied by CHs inside a
belt of around the solar equator is larger in the current 2007
solar minimum relative to the similar phase of the previous 1996 solar minimum.
The enhanced CH area is related to a recurrent appearance of five persistent
CHs, which survived during 7-27 solar rotations. Three of the CHs are of
positive magnetic polarity and two are negative. The most long-lived CH was
being formed during 2 days and existed for 27 rotations. This CH was associated
with fast solar wind at 1 AU of approximately 620 km s. The 3D
MHD modeling for this time period shows an open field structure above this CH.
We conclude that the global magnetic field of the Sun possessed a multi-pole
structure during this time period. Calculation of the harmonic power spectrum
of the solar magnetic field demonstrates a greater prevalence of multi-pole
components over the dipole component in the 2007 solar minimum compared to the
1996 solar minimum. The unusual large separation between the dipole and
multi-pole components is due to the very low magnitude of the dipole component,
which is three times lower than that in the previous 1996 solar minimum.Comment: 14 pages, 7 figure
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