Are the sunspots really vanishing?

Abstract

Context:The elapsed solar cycle (23) ended with an exceptionally long period of low activity and with unprecedented low levels for various series of solar irradiance and particle flux measurements. This unpredicted evolution of solar activity raised multiple questions about a future decline of the solar cycles and launched a quest for precursor signs of this possible deep solar transition over the last decade. Aim: We present here a review and overall interpretation of most current diagnostics of solar cycle 23, including the recent disagreements that appeared among solar reference indices and standard solar-based geo-indices, the indication of a changed pattern of internal torsional waves (helioseismology) or the announced fading and magnetic weakening of sunspots. Methods: Based on a statistical analysis of detailed sunspot properties over the last 24 years, we complete the picture with new evidence of a strong global deficit of the smallest sunspots starting around 2000, in order to answer the question: are all sunspots about to disappear? Results: This global scale-dependent change in sunspot properties is confirmed to be real and not due to uncontrolled biases in some of the indices. It can also explain the recent discrepancies between solar indices by their different sensitivities to small and weak magnetic elements (small spots). The International Sunspot Index R i , based on unweighted sunspot counts, proved to be particularly sensitive to this particular small-scale solar evolution. Conclusions: Our results and interpretation show the necessity to look backwards in time, more than 80 years ago. Indeed, the Sun seems to be actually returning to a past and hardly explored activity regime ending before the 1955-1995 Grand Maximum, which probably biased our current space-age view of solar activity.

Comparing Coronal and Heliospheric Magnetic Fields Over Several Solar Cycles

“…This is particularly clear during the last two ascending phases in 1998-1999 and in 2011-2012, and during the maximum in 1980, 2000, and in particular, during the last maximum in 2014 (see Figure 6). The large difference between the dipole and higher n max cases since the maximum of cycle 23 is most likely related to the changes in sunspots and other magnetic elements observed at this time (Svalgaard & Hudson 2010;Lukianova & Mursula 2011;Clette & Lefèvre 2012). Figure 8 shows that the polarity match percentages very rapidly approach to a limit value when increasing n max .…”

Solar surface rotation: N-S asymmetry and recent speed-up

“…The activity level in the current cycle 24 is significantly lower than in the past few solar cycles. The remarkably long and deep solar minimum and the weak cycle 24 have caused intensive attention in the solar and space physics community (Jian et al 2011;Clette & Lefèvre 2012;Wang et al 2009;Solomon et al 2010Solomon et al , 2011Cliver & Ling 2011).…”

Properties of sunspot umbrae observed in cycle 24

“…There are also indications that the population of small sunspots compared with the large ones in solar cycle 23 might be different than in previous cycles (Clette & Lefèvre 2012). This motivated us to study properties of umbrae in the current solar cycle (24) and compare them with those of previous cycles.…”