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" Long-term evolution of 27
days signal in solar activity and terrestrial magnetic indices – common
features and differences ". M.G. Shnirman (MITP RAN) Abstract: Solar
activity is known to be the origin of the short-term oscillation of The
Earth’s magnetic field. The 27-day signal created by the solar rotation is
reflected by the 27-day geomagnetic signal. We study the long-term evolution
of the 27 days signal and compare its properties for solar and geomagnetic
activity. We suggest the running averaging of 27 days’ range energy packet as
a principal tool of this study. The
27-days signal exhibits the 22-year Hale cycle whose properties are different for
sunspot numbers (Wolf number, sunspot group numbers, etc) and geomagnetic indices
(aa-index, Dst-index,
etc). The Hale cycle is manifested in the normalized aa-index
through the whole 130-years time span covered by geomagnetic indices
reflecting the non-symmetric part of the solar wind. We obtain that “short”
and “long” period in the 27-days range are differently reflected in the solar
and geomagnetic activity. Shorter periods energy has
rather similar evolution when longer periods (more than 28 days) exhibit
different behavior. The 22-years cycle in aa-index
is clearly generated by relatively “long” periods (more than 28 days), which
is not true for sunspot numbers. We discuss possible origin of this
observation. The 150
years evolution of the 27-days signal and its Hale cycle demonstrates
quasi-stationary behavior at long time intervals with a few critical moments.
One of them happens around 1915 and precedes the increase of solar activity.
Another one is observed around |
