**THE SOLAR ACTIVITY DURING THE HOLOCENE: AMPLITUDE VARIATIONS OF THE QUASY-CENTURY AND QUASI-TWO-CENTURY SOLAR CYCLES**

**Boris Komitov ^{(1)} , Boncho Bonev^{(2)} , Kaloyan Penev^{(3),} and Stephano Sello^{(4)}**

**Bulgarian Academy of Sciences- Institute of Astronomy, Bulgaria ,6003 Stara Zagora 3 POBox 39;***komitov@mbox.digsys.bg*

**(2) Laboratory for Extraterrestrial Physics, Code 690, NASA's Goddard Space Flight Center, Greenbelt, MD 20771; ***bbonev@lepvax.gsfc.nasa.gov**.*

**(3) Harvard University, Mail Stop 10, 60 Garden Street, Cambridge, MA 02138; ***kpenev@cfa.harvard.edu**.*

**(4) Mathematical and Physical Models, Enel Research, Via Andrea Pisano 120, 56122 PISA - ITALY; ***stefano.sello@enel.it**.*

- Introducton
- Methods

We summarize the recent results and prospective work in two parallel studies (Komitov; Bonev, Penev, & Sello) of the long-term trends in solar variability that can be deduced from both indirect data and optical records. Analysis' of data from ^{14}C measurements (*Stuiver et al, 1998*), aurorae (Schove series; *Schove,1983*), and direct astronomical records (group sunspot number) (*Hoyt and Shatten,1998*) focus on the stability and changes in amplitude of the cycles with duration near one and two centuries. Although these two projects have been carried independently and different methods have been used. We present them in a joint fashion in order to emphasize the common direction of their work.

The T-R periodogramm analysis for a cycles detection in times series has been used in Komitov’s study. The details of this method are described in a few works ( *Komitov 1986, 1997,2001; Benson et al. 2003*). The integral power S-parameters , which are derived on the base of results from the T-R periodogram analysis of time series (*Komitov 1999*) has been also used for estimation of the cycles magnitudes. In the second study (Bonev, Penev & Sello) a “moving windows” T-R periodogramm method as well as a multiresolution wavelet analysis has been used.

3. Results and analysis

Komitov’s study points out that a 2200 - 2500 year cycle plays an important role in the variations of the ^{14}C production rate during the last 10 000 years /Holocene /. This cycle has a likely solar origin and also shows strong climatic appearences. Its minimums correspond to the Maunder-type minima of solar activity.

Very important is the fact that the present structure and length of this quasybimillenial solar oscilation has been established about 7000 –7500 years ago. During the early part of Holocene this cycle has been shorter than now with length ~ 1800 years.

During the last ~5000 years a modulation of the solar bi-centurial cycle's amplitude by the ~2300 year cycle is observed. During the earlier part of Holocene /~ 8000 – 3000 BC/ this “modulating” supermillenial cycle is expressed as a quasyperiodic trend, which corresponds of period T »
3000 years. A more detailed analysis point out that the “critical” moment of changing the modulation regime is near to 5000 BC /fig.1/. This moment is very interesting in climatic aspect, because it is in high coincidence with the end of transited supermillenial warming after the Wurm ice epoch ( *Imbree & Imbree, 1979*) . The magnitude of the quasy-bicenturial cycle is higher near the Maunder-type minima . The results concerning the Schoves series are in a very good agreement with the aforesaid /fig. 2/.

A quasymillenial (T~ 1000 years) oscilation is most powerful in the magnitude behaviour of quasycenturial solar multiplet (70-130 years). Essentially weaker is the influence of 2200-2500 year cycle.

Bonev, Penev, & Sello examined the last 4500 years of the ^{14}C record, the continuous part of the Schove series/ AD 296 – 1996/, and the Group Sunspot Numbers. These authors applied two independent "local" methods for investigating unsteady non-linear time series: a moving windows periodogram algorithm (fig.3), and a multiresolution wavelet analysis. In their recent work Bonev, Penev, & Sello showed the changes related to the variability behavior of the quasi-century and two-century cycles on a very high scale-temporal and amplitude resolution /fig.3/. A synthesis of the peculiarities revealed in the examined solar activity proxies strongly suggested a downward trend of the long-term solar variability in the next several decades (*Bonev, Penev & Sello, 2004*).

The two parallel studies presented here propose several lines of evidence for an upcoming long-term solar variability minimum, which might be less deep than the Maunder minimum.

4. Conclusion

On the base of the above mentioned analysis it may to conclude that the obtained results by using of different methods are in a very good agreement. The comparison between results on the base of tree rings radiocarbon data and Schove’s series for the last ~1700 years are in strong coincidence too. The last one pointed out that the oldest reconstruction of large-scale structure of solar activity by D.J.Schove from AD 1955 and 1983 is not in contradiction, but rather in good agreement with the modern “cosmogenic” isothopes series.

There are evidences for a significant changes in regime of centurial and supercenturial variations of solar activity during the Holocene. A essential part of this changes is caused by modulation effects from quasibimillenial (2200-2500 year ) and quasymillenial (~ 900 –1000 year ) cycles.

About 5000- 5500 BC a serious change in the regime of large scale behaviour of solar activity has been occurred. It is characterized by establishing of the presnt structure of the 2200-2500 year cycle as well as by amplitude modulation effects of the same one over the shorter submillenial and quasycenturial solar cycles.

The amplitude modulation effects of quasybimillenial and quasymillenial cycles over the shorter (solar cycles is a very important feature of large scale variations of solar activity. It is necessary to account it if we will made a more precise solar activity forecasting model for time intervals in range of few decades or more.

Fig.1. The integral power S-parameter /S(200) / for the quasybicenturial solar cycle (170< T< 230 years) in tree-ring radiocarbon series during Holocene. The “shock” near 5000 BC is clear visible. During the recent Holocene (b) a strong ~2300 year cycle in S(200) series exist.

Fig.2. The integral power S-parameter /S(200) / for the quasybicenturial solar cycle (170< T< 230 years) in Schove’s series (AD 296 – 1996).

Fig.3. A two-dimensional T-R correllogramm of tree ring radiocarbon series for the last ~4500 years. For every separate T-R procedure a moving window of 800 years has been used. The mean time interval between local maximums of correlation coefficient R for period T~ 200 years is about 2200-2300 years (*Bonev, Penev and Sello, 2004*).

REFFERENCES

Benson J.L., Bonev B,James Ph. ,Shan K, Cantor P.,c and Caplinger M ., The seasonal behavior of water ice clouds in the Tharsis and Valles Marineris regions of Mars: Mars Orbiter Camera Observations, 2003, Icarus v.165 pp 34–52

**Bonev B., Penev K. and Sello S,** **Long –Term Solar Variability and the Solar Cycle in the XXI Century, **RY**2004, Astrophys J. Lett, L81-84,Apr.10**

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Komitov, B., On a Possible Effect of Solar Cycles on the Climate of Bulgaria, *Solar Dat*a, 1986, No. 5, pp.73–78.

Komitov, B., The Schove’s Series: Centurial and Supercen-turial Variations of Solar Activity. Relationships between Adjacent Solar Cycles, Bulg. Geophys. J., 1997, vol. 23, No.1-2, pp. 69–79.

Komitov, B.,To Problems of Stability of the 100- and 200-Year Solar Cycles * *(Rep. 6th National Conf. On Sun –Earth Physics), Sofia, 1999, pp. 185–187.

Komitov, B., *T–R *Periodogram Analysis, Chronobiologiya I biometeorologiya v bulgarskata meditsina (Chronobiology and Biometeorology in Bulgarian Medicine), Madzhirov, N., Ed., Plovdiv: 2001, pp. 30–31.

Hoyt, D. and Schatten, K., Group Sunspot Numbers: A New Solar Activity Reconstruction, *Solar Phys*., 1998, vol.181, No. 2, pp. 491–512.

Imbree J. and Imbree K,. The Secret of Ice Epochs /Russian Edd./,1988, Mir, Moscow

**Schove, D.J., Sunspot Cycles , Stroudsburg: Hutchinson Ross, 1983**.

M. Stuiver, P. J. Reimer, E. Bard, J. W. Beck, G. S. Burr, K. A. Hughen, B. Kromer, F. G. McCormac, J. v. d. Plicht and M. Spurk. INTCAL98 Radiocarbon Age Calibration, 24,000-cal BP. Radiocarbon 40, 1041-1083 (1998).