69 research outputs found
Specific interplanetary conditions for CIR-, Sheath-, and ICME-induced geomagnetic storms obtained by double superposed epoch analysis
The comparison of specific interplanetary conditions for 798 magnetic storms
with Dst < -50 nT for the period 1976-2000 was made on the basis of the OMNI
archive data.We categorized various large-scale types of solar wind as
interplanetary drivers of storms: corotating interaction region (CIR), Sheath,
interplanetary CME (ICME) including magnetic cloud (MC) and Ejecta, separately
MC and Ejecta, and "Indeterminate" type. The data processing was carried out by
the method of double superposed epoch analysis which uses two reference times
(onset of storm and the minimum Dst index) and make a re-scaling of main phase
of storm a such way that after this transformation all storms have equal
durations of main phase in new time reference frame. This method reproduced
some well-known results and allowed us to obtain some new results.
Specifically, obtained results demonstrate high importance of Sheath in
generation of magnetic storms as well as a significant differences in
properties of MC and Ejecta and in their geoeffectiveness.Comment: 21 pages, 9 figures, 1 table, submitted to J. of Advances in Space
Research on 29 July, 2009 for Special Issue "Space Weather Advances
Geomagnetic storm dependence on the solar flare class
Content. Solar flares are often used as precursors of geomagnetic storms. In
particular, Howard and Tappin (2005) recently published in A&A a dependence
between X-ray class of solar flares and Ap and Dst indexes of geomagnetic
storms which contradicts to early published results.
Aims. We compare published results on flare-storm dependences and discuss
possible sources of the discrepancy.
Methods. We analyze following sources of difference: (1) different intervals
of observations, (2) different statistics and (3) different methods of event
identification and comparison.
Results. Our analysis shows that magnitude of geomagnetic storms is likely to
be independent on X-ray class of solar flares.Comment: 3 pages, 1 tabl
Comment on "Geoeffectiveness of halo coronal mass ejections" by N. Gopalswamy, S. Yashiro, and S. Akiyama
Comment on paper: Gopalswamy, N., S. Yashiro, and S. Akiyama (2007),
Geoeffectiveness of halo coronal mass ejections, J. Geophys. Res., 112, A06112,
doi:10.1029/2006JA012149
Gopalswamy et al. [2007] studied the geoeffectiveness of halo coronal mass
ejections (CMEs) on the basis of solar observations during 1996-2005 and found
that the geoeffectiveness of 229 frontside halo CMEs was 71%. Recently for
observations of 305 frontside halo CMEs during 1997-2003 the geoeffectiveness
was found to be 40% [Kim et al., 2005]. Complex analysis of both solar and
interplanetary measurements showed that the geoeffectiveness of frontside halo
CMEs is likely to be about 50% [Yermolaev et al., 2005; Yermolaev and
Yermolaev, 2006]. Gopalswamy et al. [2007] did not discuss possible causes of
this difference and were limited only to the general words: "The reason for the
conflicting results (geoeffectiveness of CMEs ranging from 35% to more than
80%) may be attributed to the different definition of halo CMEs and
geoeffectiveness." So, here we shall present our point of view on high
geoeffectivenees of CME obtained in paper by Gopalswamy et al. [2007]
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