Statistical properties of flares/sunspots over the solar cycle

Transcription

1 Statistical properties of flares/sunspots over the solar cycle M. Temmer Kanzelhöhe Observatory/IGAM, Institute of Physics University of Graz, Austria M. Temmer: Statistical properties of flares/sunspots over the solar cycle 1

2 Smithsonian Contribution to Astrophysics, Vol. 3, p.25, years later M. Temmer: Statistical properties of flares/sunspots over the solar cycle 2

3 The variability of the Sun Regular observations of the corona were starting in the 60 s of the last century: OSO1-8, Skylab, SMM, Spacelab, Yohkoh, GOES, SOHO, Hinode, STEREO, The changing Sun as observed in X-ray. Yohkoh/SXT from 1992 until The photospheric magnetic field over the solar cycle. NSO at Kitt Peak M. Temmer: Statistical properties of flares/sunspots over the solar cycle 3

4 Measurement of solar activity flares, CMEs SOHO/EIT 195A Flares in H-alpha, SXR, HXR energy release particle acceleration coronal mass ejections regular H-alpha data since 1940 s Mann et al M. Temmer: Statistical properties of flares/sunspots over the solar cycle 4

5 Measurement of solar activity sunspots Wolf number, the basic formula: R=k (10g+s) Ri: International Sunspot Number calculated from > 25 stations at the SIDC (Belgium) Sunspot numbers have the link with the past; data since 1600 s Sunspot areas - data since 1874 Relation to other activity indices? Part of a sunspot group near disk center (July 15, 2002) observed with the Swedish Solar Telescope (La Palma) M. Temmer: Statistical properties of flares/sunspots over the solar cycle 5

6 Flare occurrence over the solar cycle Flare rate and Ri (monthly averaged) vary by a factor ~20 over the solar cycle Ri is a measure of the total magnetic flux (detoma et al. 2000) Total soft X-ray luminosity (I SXR ) scales with the magnetic flux B (longitudinal component) I SXR ~<B> 2 Benevolenskaya et al from Aschwanden, 1994 The flare rate (SXR, HXR) has to be related to the available magnetic flux (free magnetic energy) on the solar surface. M. Temmer: Statistical properties of flares/sunspots over the solar cycle 6

7 Relation between flare rate and Ri / sunspot area Plots: cycle 19 (thick line), 20 (thin line) 19, 21, 23 shift of months between Ri and H- alpha flare rate lag more prominent for high energetic flares (H-alpha II*) 22-year variation infers close connection to solar dynamo Gnevyshev-Ohl, 1948; Cliver et al. 1996; Mursula et al., 2001; Cliver & Ling, 2001; Gnevyshev-Ohl rule? (violated with cycle 23) Temmer et al M. Temmer: Statistical properties of flares/sunspots over the solar cycle 7

8 Relation between HXR flares and Ri lag between solar cycle indices and HXR flare rate during cycle 21 Bai, 1993; Bromund et al., 1995 most outstanding events occur after maximum Svestka, 1995 Cycles #X-class flares Dynamic energy balance in the corona? Wheatland & Litvinenko, 2004 > different activity behavior of the two parts of the magnetic 22-year solar periodicity solar interior dynamics. Hudson, 2007 Diamonds show years during declining phases ( , , and ). M. Temmer: Statistical properties of flares/sunspots over the solar cycle 8

9 Frequency distributions of HXR flares Power-law distribution of flare-related phenomena Dennis, 1985; Hudson, 1991 Avalanche model of solar flares, does not expect any changes over the cycle Lu & Hamilton, 1991 Crosby et al., 1993 invariance of slope in the course of the solar cycle for HXR flare occurrence Crosby et al., 1993; Lu et al., 1993 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 9

10 Distributions of SXR flares during minimum the power-law extends to smaller peak fluxes, since during these periods also less intense flares can be detected cycle 22 the power-law index does not reveal any remarkable change in the course of the solar cycle similar outcome for 6-12 kev frequency distribution (RHESSI data) during cycle 23 Christie et al., 2008 M. Temmer: Statistical properties of flares/sunspots over the solar cycle Veronig et al

11 SXR background flux (XBF) and Ri GOES 1-8A flux ( ) Delay of peak XBF for cycles 21, 23; no delay for cycle 22 Pearce, 1992; Wilson, 1993; Aschwanden, 1994; Relation XBF and SN: power law fit values differ 21, Veronig et al M. Temmer: Statistical properties of flares/sunspots over the solar cycle 11

12 North-south (N-S) asymmetry N-S asymmetry is real; not due to random fluctuations Carbonell et al., 1993 found for various kinds of solar activity indices, sunspots (Ri, areas, groups, magnetic classes, etc.), flares, prominences, radio bursts, hard X-ray bursts, gammaray bursts, CMEs Roy, 1977; Garcia, 1990; Joshi, 1995; Li et al. 1998; Atac & Özguc, 2001; Brajsa et al. 2005; Knaack et al. 2005; Carbonell, 2007; Asymmetry most significant during solar minimum Temmer et al., 2001 N-S asymmetry changes every four cycles hint of long-term periodic behavior of 8 cycles Vizoso & Ballester, 1990; Li et al., 2009 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 12

13 North-south (N-S) asymmetry Northern hemisphere dominates soon after minimum; south at the end of the cycle Garcia, 1990; Bai, 1987, 1988; Average rotational periods differ between northern and southern hemisphere Temmer et al., 2002; Joshi et al Hemispheres coupled weakly during the cycle Indication of 22-year alternation N S S N S N Temmer et al., 2002 Li et al., 2009 Swinson & Derek, 1986 * triangles indicate solar max. M. Temmer: Statistical properties of flares/sunspots over the solar cycle 13

14 Coronal mass ejections Data CACTus CDAW most violent signatures of solar activity; most geoeffective occurrence rate varies between 6/day and 0.5/day for solar max and min. mean and median speeds vary by an order of magnitude over the solar cycle Gopalswamy et al., 2003; Yashiro et al., day sequence of SOHO/LASCO C3 observations during the high activity phase in Oct/Nov Robbrecht, Berghmans, Van der Linden 2009 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 14

15 Relation between CMEs and sunspot number CME cycle lags sunspot cycle 23 For cycle this effect was not clearly present Webb & Howard 1994 peculiarity of cycle 23? on average halo CMEs are less during minimum projection effects (STEREO) Robbrecht, Berghmans, Van der Linden 2009 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 15

16 Relation between CMEs and sunspot number just like the sunspot number the CME rate steeply rises and decays slowly after solar maximum for the same number of sunspots, more CMEs are produced during the decaying phase are these sunspots more active? it could also mean that more CMEs erupt from nonsunspot regions e.g. Robbrecht, Patsourakos, Vourlidas, 2009 Robbrecht, Berghmans, Van der Linden 2009 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 16

17 Coronal holes low density, low temperatures, open magnetic field lines allows solar wind, energetic particles to escape to IP space (e.g., Fisk, 2005) multiwavelength observations of CHs (de Toma & Arge, 2005) magnetic net flux density inside coronal holes increases with rising solar activity (Harvey et al., 1982; Kitt Peak data) EIT 284A showing CHs during min and max. NSO coronal hole map extracted from He I 1083 nm M. Temmer: Statistical properties of flares/sunspots over the solar cycle 17

18 Coronal holes driver of solar-terrestrial impacts HSS during minimum activity Schwenn 1983; Crooker & Cliver 1994 CIRs during decline phase Webb, 1995; Gopalswamy, 2005 density net flux weakly correlated to the area of CHs Abramenko et al., 2009 Vrsnak, Temmer, Veronig, 2007 solar wind speed, Dst index, related to the area of CHs Robbins et al., 2006; Vrsnak et al M. Temmer: Statistical properties of flares/sunspots over the solar cycle 18.mov

19 How peculiar is this solar minimum? grand minima/maxima are not a result of long-term cyclic variations but defined by stochastic/chaotic processes Usoskin et al., 2007 solar activity during the past 70 years is exceptional (equally high activity more than 8,000 years ago) Solanki et al., 2004 end of grand maximum in solar magnetic activity within the next 2-3 solar cycles Abreu et al., 2008 Modern Maximum (1920?) M. Temmer: Statistical properties of flares/sunspots over the solar cycle 19

20 How peculiar is this solar minimum? #consecutive days with Ri=0: Sunspot relative number (Ri) #consec. days with Ri=0: 31 M. Temmer: Statistical properties of flares/sunspots over the solar cycle 20

21 How peculiar is this solar minimum? Cumulative number of spotless days during a cycle Pötzi, 2009 Solar cycle 23 is comparable to cycle 14 (ended 1913) there is nothing peculiar about this minimum (not yet?) M. Temmer: Statistical properties of flares/sunspots over the solar cycle 21

22 The end of high minima? 19 fleet of spacecraft observing the Sun: SOHO, GOES, RHESSI, ACE, TRACE, STEREO, Hinode, Coronas-F, SDO (soon), Proba2 (soon), etc., in addition to ground-based observatories space era started during times of high minima - the current minimum disappoints do we return back to a normal level of solar activity? M. Temmer: Statistical properties of flares/sunspots over the solar cycle 22

23 Conclusions 1) Flares (high energetic) and XBF evolve not in phase with the relative sunspot number/area for odd numbered cycles 22-year varation shows a strong relation to magnetic activity cycle; CMEs? 2) North-South asymmetry: real, indication of 22-year variation >> Important constraints from observations for solar dynamo models 3) Flare distribution (power-law): slope is invariant with respect to the solar cycle phases (min. versus max.), differences for minima and maxima with respect to high end energy (intensity threshold) 4) Coronal hole areas: during solar minimum clear relation to solar wind speed and geomagnetic effects (HSS, CIRs) - solar cycle relation tricky to establish due to other contributions especially CMEs 5) Nothing yet peculiar about the current minimum (for how long?); how about the next cycle? End of high activity? M. Temmer: Statistical properties of flares/sunspots over the solar cycle 23