Summary: The Solar Activity in the Miocene Period
In this Subthesis we study the solar activity in the Miocene (or Triassic)
period. Measurements of the thickness of the annual tree­rings of petrified
trees provide a unique method to determine the cycle of the solar activity
during the life­time of the tree in pre­historic times. Study of annual tree­
rings of 12 different petrified trees from the Miocene (or Triassic) period show
solar cycles with a period of 6:8 \Gamma 8:4 years in contradiction to the recent
average 22­year­period.
1 Introduction
Modern solar observations show that the Sun varies on time scales of minu­
tes (radio bursts, flares) to weeks and months (sunspots) up to years (global
magnetic field variation with a period of 22 years). Although the period of
the observations is not so long, 387 years only, direct observations of the
surface of the Sun show changes of even longer periods; e.g. a cycle of vari­
ation obtained from the envelope of the annual mean sunspot numbers with
a period of 80 \Gamma 90 years (the Gleissberg cycle).
The time variations of the Sun can be divided into two classes: (i) those
that are visible on the surface of the Sun (e.g. sunspots, faculae, solar fla­
res, eruptive prominences, changes of the general magnetic field of the Sun);
(ii) changes observed at the Earth in the form of an energy and/or particle

Source: Armagh Observatory

Collections: Physics