|
|
| Figure 4 |
[10] The known laws in the geomagnetic storm development are clearly seen: Long and strong negative values of Bz correspond to the geomagnetic storm enhancement, when similar, but positive values lead to the geomagnetic storm cessation and weakening Akasofu et al., 1985; Gonzalez et al., 1999, 2004; Intriligator et al., 2005; Yurchyshyn, 2004 (available at http://sprg.ssl.berkeley.edu/RHESSI/rst/abstracts/yurchyshyn.txt)]. We have indicated by eight arrows the corresponding time intervals in Figure 4, which demonstrate the temporary cessation or blocking in the geomagnetic storm development [Gonzalez et al., 2004]. It is possible in this way to reconstruct the interplanetary conditions using magnetograms obtained on the ground for large historical geomagnetic storms of the past, when direct magnetic field measurements in the prespace era had not started or were not available in more recent history. It would be interesting to perform the comparative study in this direction using archives for the known historic geomagnetic storms [Chapman and Bartels, 1940; Sugiura and Chapman, 1960; Tsurutani et al., 2003; Veselovsky et al., 2005a, 2005b]. Unfortunately, the available lists of "remarkable," "violent," or "great" storms are far from being complete and homogeneous in sense of the selection criteria.
[11] As for the solar origins of heliospheric perturbations, we
should note early results on erupting prominences demonstrating
velocities of the orders from tens up to hundreds kilometers per
second
[Akasofu and Kamide, 2005;
Tsurutani et al., 2005;
Veselovsky, 1996].
CMEs can move even faster, up to more than
2000 km s
-1, and drive piston or blast waves ahead. In that case
for the self-similar spherically symmetric situation for extremely
strong shock one can apply dimensionless scaling estimate for
the speed of its front
V
(2/5)E1/5 r-1/5t-3/5,
where
E is the
released free energy,
r is the density of the homogeneous
atmosphere, and
t is the time after explosion. For the stratified
atmosphere the deceleration of the shock can be expressed in a
more complicated manner, but the principal ideas remain valid.
In the case of the kinematic self-similarity, the evolution of the
plasma velocity obeys the purely geometric law
V R/t, which is
independent on the background and perturbation parameters.
These asymptotic regimes indicate only extreme or intermediate
behavior, and numerical solutions are needed in each case for
matching them and obtaining realistic numbers, as usual in
problems of this type for real geometry and initial conditions in
the inhomogeneous background.
[12] One more comment should be made on the absence of any cause-sequence relation between CMEs and solar flares. In spite of this obvious fact, many fruitless attempts are still found in the current literature to establish such unphysical connections. Both phenomena are merely electromagnetic and plasma manifestations of the same dissipation process of the free energy in the solar corona. They can proceed nearly simultaneously and demonstrate their peaks coinciding in time with the reasonable accuracy of the order of their time duration, or being sometimes earlier, or later each against other in this sequence. It was shown both theoretically and observationally [Akasofu and Kamide, 2005; Pettit, 1946; Tsurutani et al., 2005]. Maximal acceleration of the CME can be observed a little bit before or after the maximal brightness of the flare. This time sequence is interesting for the study of the details but not for the establishment of causes and sequences. The questions: What is the first? What is primary, flare or CME?, has no deep physical meaning. They are ill-posed and have no correct answer. There is no relation in this case.
[13] Several comments are in order regarding CME prominence relations. Many studies of the recent years can be summarized as follows. CMEs can be formed even if the prominence was not erupted, but only "activated." The discrimination depends on the criteria and is not quite objective. In any case, big CMEs without appreciable changes beneath them are not common and could be related to the cases with not sufficient information, sensitivity, resolution, etc. Free energy releases high in the corona independent of lower boundary conditions just due to local instability are possible in principle. However, such cases of "independence" are not known for big events. Hence we should again think about physically open systems but not closed ones. All eruptive prominences are accompanied by the CME formation.
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