Unusual structure of sunspot cycle 24* H. S. Ahluwalia, University of New Mexico, Albuquerque, NM, USA. *Solar data used in this analysis are available at: http://sidc.oma.be/silso/ and http://www.ngdc.noaa.gov/stp/solar/flux.html.

Data Fig 1 b, c. SSN v/s F10.7 for (b) 1952-1986, and (c) 1987-2009 Fig 1a. Yearly SSN (black), F10.7 (red) in sfu (1 sfu = 10-22Wm-2Hz-1 ) for 1947-2014; thick lines are 11y mean, arrow indicates the point of steeper descent for SSN. Yearly SSN, F10.7 track well; cc = 0.99. Both have 11y period and reach min in the same year. Typically, SSNs rise to a peak and descend to a variable min (~ 0), cycles 18, 23 have deeper min. F10.7 reaches min at the same time as SSN at ~ 60 sfu for each cycle. Cy 22 has a double peak for both; for cy. 24 they have a plateau and steep rise to a peak. Decreasing trend exists for 11y means starting near the minimum of cycle 21 (see arrow, SSN decline is slightly steeper than F10.7 (see Fig.1b, c) implying that relationship between them is drifting, calling into question the assumption that there is a close match between them. Yearly SSN and B are related (cc = 0.94) [Ahluwalia, 2013] so one should explore how F10.7 relates to solar fields [Henney et al., 2012 ]. Ahluwalia [2012] argues that sun is transitioning to a low activity state in a complex way leading to a Dalton-like grand minimum (DM) in the twenty-first century. Fig 1 b, c. SSN v/s F10.7 for (b) 1952-1986, and (c) 1987-2009

Unusual Structure of Cycle 24 Fig. 2. Growth for cycles 15 (green), 24 (black) compared with F10.7 (red) for 72 months after onset. Cy 24 has a shoulder in Feb-Mar 2012, it lingers near plateau in 2013 and develops a peak in Oct 2014 due to activity in S-hemisphere, after polar fields reversed. Polarity reversed in N-hemisphere in June 2012 and again in Feb 2014 while that in S-hemisphere reversed in June 2013. Cy 24 follows timeline of Cy 15 and F10.7 for 14 months, afterwards the rise of Cy 15 is steeper and F10.7 flatter. F10.7 profile has same features as Cy 24 but peak occurs two months later (cause unknown). Cy 24 ascent is consistent with Ahluwalia and Jackiewicz [2012] – AJ12 hereafter – prediction but peak SSN is 25% higher. Cy 24 mimics development phase of Cy 15 that also reached a plateau but rose to a higher peak, the delayed peak for Cy 24 is not as conspicuous as that for cycle 15 and occurs later in timeline. The decay phase has set in for both indices.

Sunspot Cycle 25 If TCQP [Ahluwalia,2000] endures, Fig 3. Comparison of SSN growth for six cycles (4, 5, 6, 7, 14, and 24) for 72 months after onset. If TCQP [Ahluwalia,2000] endures, AJ12 predict next 2 cycles may be less active than CY 24 leading to a DM-like. Some argue next minmum will be Maunder-like (MM). But Zolotova and Ponyavin [2015] argue MM is not as grand as it seemed to be because of under-reported SSNs by some observers. Key parameters (Rm, Tr) for next cycles cannot be predicted now but we may speculate about Cy 25 from a historical perspective. Cy 5, 6, 7 are significantly less active than CY 4; they define DM (1790-1830); Mt Tambora volcanic eruption (1815) happened in Cy 5 [Wood, 2014] Cy 6 is less active than cycle 5 and Cy 7 is more active than Cy 5 and 6, leading out of DM, it has a long (> 12y) duration Cy 14 defines the Gliessburg minimum (GM), it is significantly more active than Cy 5, 6, and indicating that GM is not a grand minimum.

Space Weather Speculations 1. Since SSNs may decrease successively for the next two cycles, the value of B at 1 AU [Ahluwalia, 2013], frequency of fast CMEs, SSCs (storm sudden commencements) and large Forbush decreases at 1 AU shall all decrease in future [Ahluwalia and Kamide, 2005; Ahluwalia et al., 2007], lower than anytime during the space age, accompanied by a significant increase in low energy GCRs [Ahluwalia and Ygbuhay, 2010; Mewaldt, 2010] and reduced ionosphere disturbances. 2. An occurrence of an extreme CME in future cannot be ruled out [National Research Council Report, 2008], 1859-like CME could cause a global blackout today. Clark [2007] gives a riveting account of Carrington observations and global havoc caused by the 1859 CME. 3. An extreme CME occurred in July 2012, detected by STEREO satellites [Baker et al., 2013], it was directed away from earth. Vasyliunas [2011] argues that worst case SSC cannot be more than ~ 40 % stronger than the 1859 Carrington event SSC [Gonzalez et al., 2011]. 4. Space weather effects are poorly quantified for any type of space storm, particularly larger ones that might hit earth [Schrijver and Beer, 2014].

Conclusions 2. The decay phase of cycle 24 is continuing: 1. Cy 24 with onset in Dec 2008 lingered near a shoulder in 2013 and reached a delayed peak in Oct 2014 well after reversals of polar fields due to enhanced activity in southern hemisphere, differing from timeline of a typical SSN cycle that rises to a peak and decreases to a variable minimum (~ zero). 2. The decay phase of cycle 24 is continuing: Physical cause(es) for the conspicuous north-south asymmetry in SSNs is not understood yet [Shetye et al., 2015]. SSNs declined at a faster rate than F10.7 starting near cycle 21 minimum and F10.7 reached the peak two months after SSN peak for cycle 24. Physical cause(es) for these differences are not known calling into question the assumption (unproven) that there is a close match between two indices. 3. Predictions for key parameters for cycle 24: Fell short [Pesnell, 2012], some were close [Schatten, 2005; Svalgaard et al., 2005; AJ12], others wide off the mark [Dikpati et al; 2006]. We do not yet understand how the solar Dynamo works. 4. If TCQP endures, next two cycles (25, 26) shall be successively less active and the phenomena that track SSNs shall be significantly affected. 5. We are entering a new era where value of B, frequency of fast CMEs, SSCs (storm sudden commencements) and large Forbush decreases at 1 AU shall all decrease, lower than any time during the space age, followed by a significant increase in low energy GCRs and reduced ionosphere disturbances. An extreme CME occurrence cannot be ruled out in future. THANK YOU!!

New Smooth SSNs CAUTION!! On 1 July 2015 a brand new smooth SSN time series (Version2) was launched at http://sidc.oma.be/silso/, after a careful re-calibration of the historic series (Version1). The plot shows a comparison of V1 and V2 for cycles 15 and 24, in relation to F10.7. We are in the process of ascertaining what effect this change will have on results reported by us in the past using V1. Stay tuned!