Saturday, September 13, 2008

Predictions of deep solar minimum

Makarov et al 2001

Indeed our analysis shows that the magnetic flux from the Sun increases by a factor of 1.4 since 1964 and this agrees with the observations. But we have found an increase of polar magnetic field strength (Bp) from the observations of the annual mean number of polar faculae (Npf ) in this period. Consequently the mean polar magnetic field _Bp_ has been estimated of 2.5 G in cycle 21 and 4.0 G in cycle 23, i.e., an increase by a factor of 1.6. Hence there was an increase of the value of the polar field of the Sun, but on an interval of time of about two to three 11-year cycles. Long-term increase of magnetic flux from the Sun was mainly caused by growth of the area of polar cap of the Sun occupied by the unipolar magnetic field.

A new index of polar activity of the Sun _Apz_ (area of polar cap occupied by a unipolar fields) has been compared with the aa, W and A-index. We used the correlations between _aa_ and _Apz_ to estimate the limit latitude of the highlatitude zone boundary θ2m to be about 60. Its minimum is < 38, the present value.We suggest that θ2m practically coincides with the conical blades where rω = 0 and thus that these conical blades have a similar oscillatory motion between say 60and < 38. It is supposed that deep minima of solar activity may occur when these conical blades reach extreme latitudes. This may be an indication that we are approaching a new deep minimum.

The relation between the concentration of 14C and solar activity is well known. Stuiver and Quay (1980) have detected a few periods of very low activity of the Sun: the Maunder Minimum (1645–1715), the Spörer Minimum (1416–1435, 1470–1534), the Wolf Minimum (1282–1342) and, probably, the Oort Minimum (1010–1050). The mean duration of low activity is about 60 years and the mean length of time between the minima is about 220 years, or about 20 solar cycles. This corresponds to a latitude drift of the zone boundary of 24. Again this is an indication that the Sun may be turning soon (in 1 or 2 cycles?) into a period of low activity with a duration of about 60 years. Some other papers also predicted the period of very low solar activity at the beginning of the XXI century (Chistyakov,1983; Badalyan, Obridko, and Sýkora, 2001).

One may wonder whether there is a contradiction between Apz increasing (and contributing to global warming) and a grand minimum. However, a grand minimum may constitute a phase of reorganization so that θ2m and θ1m occur again at higher latitudes. Anyway in a grand minimum the activity becomes so low that the corresponding flux practically vanishes.

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