Anomalously extended minima of solar cycle 23
Ambika Singh, Anil Kumar Tiwari and S. P. Agrawal

Millennium Institute of Technology and Science, Bhopal
E-mail: ambika.physics@gmail.com

Abstract. The new millennium extended solar minimum of solar cycle 23 (2007-2009) contains some distinct surprises and is anomalous in comparison to the past few solar cycles. In general, the level of solar activity goes through the cyclic changes lasting roughly 11 years. The last solar cycle 23 started in the year 1996 and was expected to last until 2006. Nevertheless, the solar activity minima continued beyond the year 2006 and lasted till 2009. In fact, anomalously, during the years 2007-09, a deep sunspot minima was observed at the end of the last solar cycle 23. It is observed that the sun had no sunspots continuously for over 50 days in July-August, 2009. More so, it is found that the solar cycle 23 has the longest quiet period as compared to the last many previous solar cycles. Anomalously low values of the geomagnetic disturbance Ap is observed during the whole quiet period (2007-09) of the sun, particularly in the month of January-September 2009, during which the high speed solar wind streams are also not observed. As such, the past solar cycle 23 seems to have the very long period of about 14 years, which is anomalously distinct from previous four solar cycles, besides the obvious Ap correlation of very low activity. The low values of the sunspot numbers in years 2007-2009 also have a very distinct effect in producing lowest modulation in cosmic ray intensity, with highest values of neutron monitor counts observed in the year 2009, as compared to that observed so far in previous solar cycles. These results are discussed in the light of many associated solar-terrestrial phenomena.