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Multi­Wavelength Investigations of Solar Activity
Proceedings IAU Symposium No. 223, 2004
A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev, eds.
c
# 2004 International Astronomical Union
DOI: 00.0000/X000000000000000X
Solar cycle 23 analysis
Georgeta Mari›s 1 , Miruna Daniela Popescu 1,2
and Diana Be›sliu 1
1 Astronomical Institute of the Romanian Academy Str. Cutitul de Argint 5, RO­040558 1
Bucharest, Romania e­mail: gmaris@aira.astro.ro
2 Armagh Observatory, College Hill, Armagh, BT61 9DG, N. Ireland email: mdp@arm.ac.uk
Abstract. We analyse the solar cycle (SC) 23 behavior. We also make a comparison with some
previous cycles and present a few aspects concerning the forecasts made for SC 23 maximum.
As regards the following cycle, in accordance to other early predictions, our empirical method,
based on observing the flare energy release during the descendant phase of the precedent SC,
estimate that the amplitude of SC 24 will be low.
1. Previous forecasts and a short review of SC 23
A large range of forecasting methods is used to predict the occurrence and ampli­
tude of SCs. They have changed from simple statistical (nonlinear) to complex physical
(precursor), based on the understanding of the dynamo process that generates the solar
magnetic field and its evolution (Joselyn (1997); Sello (2003); Schatten et al. (2003)).
According to the smoothed sunspot relative number (SSR no.), SC 23 began in May
1996. Based on many prediction methods, it was originally expected to reach a magnitude
comparable to SC 21 (SSR 21
max = 164.5) and even higher. A summary of forecasts for
its maximum is given by Mari›s et al. (2003). SSR 23
max was expected to be between 140
and 200, with the exception of a climatologycal method, which had an estimation of
115. SC 23 maximum level was SSR 23
max = 120.8, reached in Apr. 2000, with a second
(smaller) maximum in Nov. 2001, of 115.5.
The SSR no. for SCs 20 to 23 is given in Fig. 1 a. For SC 23 current data are only for
90 months from its minimum (May 1996 ­ Dec. 2003). The SSR of SC 23 is lower than
for SCs 21 and 22 and closer to SC 20. Previous SCs with similar SSRmax (see Fig. 1 b)
had lengths between 9 yr and 1 month (SC 2) and 11 yr and 10 months (SC 11). SC 23
seems to be much alike SC 17, which had a length of 10 yr and 6 months.
The first SC 23 active region (AR) emerged in May 1996 -- late, in comparison with
previous SCs, therefore it might give a hint on the cycle's slow amplification and low
activity level. SC 23 ARs became predominant over the ones of SC 22 after Feb. 1997. Its
ascending phase starts to develop in Sept. 1997. On its descending phase, SC 23 had a
series of long duration ARs, e#cient in high energy eruptive events. They took place in:
Jul. 2000, Mar. ­ Apr. 2001, May ­ Jun. 2002 and Oct. ­ Nov. 2003 (Mari›s et al., 2002).
We think that by looking at those pulses on the descending phase, which are more
obvious in flare energy release indices than in SSR, we can have information about the
activity in the current cycle, and even about the appearance of the following one. Those
ARs might appear because of the interaction between the magnetic fields, belonging to
the old and to the new solar cycle, with a reversed dipole. This behavior of flares could
explain the ''abnormal'' and unpredicted appearance of SC 23. The new magnetic dipole,
responsible for SC 23 activity, began to lose part of its energy even during the descending
phase of SC 22, so that the activity of SC 23 proves to be well below predicted values.
1

2 G. Mari›s et al.
Figure 1. (a) the SSR no. for SCs 20 to 23. For SC 23 current data are only for 90 months from
its minimum (May 1996 to Dec. 2003); (b) previous SCs with similar maximum values for SSR
as compared to SC 23 (SSR 23
max = 120.8): SC 2: 9 yr and 1 month, SSR 2
max = 115.8; SC 10: 11
yr and 4 months, SSR 10
max = 98.0; SC 11: 11 yr and 10 months, SSR 11
max = 140.3; SC 15: 10 yr
and 1 month, SSR 15
max = 105.4; SC 17: 10 yr and 6 months, SSR 17
max = 119.2; SC 20: 11 yr and
9 months, SSR 20
max = 110.6. In (b) each cycle was lifted with 40 units for clarity.
2. Some early forecasts for SC 24
Preliminary estimations for the following SC support a tendency towards a reduction
in the intensity of solar activity. Using a solar dynamo precursor method, Schatten and
Tobiska (2003) predict a rapid decline, starting with SC 24. They estimate that the Sun
may be heading towards a ''Maunder'' type of minimum -- an extensive period of reduced
levels for activity. Sello (2003) uses both a nonlinear and a precursor method, giving a
peak amplitude as SSR 24
max = 96 ± 25, occurring in Apr. 2011 and as 115 ± 21 for 2011,
respectively. Another early nonlinear prediction (SSR 24
max = 87 ± 23.5) was given by
Duhau (2003), who also presents evidence that solar activity is in a decline that started
in 1993.
According to our empirical method of estimating the solar activity, based on observing
the flare energy release during the descendant phase of the precedent SC, the recent
events from Oct. ­ Nov. 2003 and the likely existence of some upcoming similar ones
make us agree that the amplitude of SC 24 is going to be low.
Acknowledgements
G. M. would like to acknowledge the receivement of an IAU travel grant.
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