statistical properties of flares/sunspots over the solar cycle€¦ · m. temmer: statistical...

M. Temmer: Statistical properties of flares/sunspots over the solar cycle 1SOHO 23, Northeast Harbor, Maine, 21 – 25 September 2009

Statistical properties of flares/sunspots over the solar cycle

M. Temmer

Kanzelhöhe Observatory/IGAM, Institute of Physics University of Graz, Austria


Smithsonian Contribution to Astrophysics, Vol. 3, p.25, 1959 50 years later…


The variability of the Sun

The changing Sun as observed in X-ray. Yohkoh/SXT from 1992 until 1999.

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 photospheric magnetic field over the solar cycle. NSO at Kitt Peak 1992-1999.


Measurement of solar activity – flares, CMEs

Mann et al. 2008

SOHO/EIT 195A

Flares in H-alpha,SXR, HXR

energy release

particle acceleration

coronal mass ejections

regular H-alpha data since 1940‘s


Part of a sunspot group near disk center (July 15, 2002) observed with the Swedish Solar Telescope (La Palma)

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?

Measurement of solar activity – sunspots


Flare occurrence over the solar cycle

from Aschwanden, 1994

Total soft X-ray luminosity (ISXR) scales with the magnetic flux B (longitudinal component)

ISXR ~<B>2

Benevolenskaya et al. 2002

The flare rate (SXR, HXR) has to be related to the available magnetic flux (free magnetic energy) on the solar surface.

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)


Relation between flare rate and Ri / sunspot area

Temmer et al. 2003

19, 21, 23 – shift of 10-15 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 rule? (violated with cycle 23)

Gnevyshev-Ohl, 1948; Cliver et al. 1996; Mursula et al., 2001; Cliver & Ling, 2001;

Plots: cycle 19 (thick line), 20 (thin line)


Relation between HXR flares and Ri

Bai, 1993; Bromund et al., 1995

lag between solar cycle indices and HXR flare rate during cycle 21

most outstanding events occur after maximum

Diamonds show years during declining phases (1983–1985, 1993–1995, and 2004–2006).

15 034

Hudson, 2007

Cycles 21 22 23

Dynamic energy balance in the corona?

Wheatland & Litvinenko, 2004

Svestka, 1995

> different activity behavior of the two parts of the magnetic 22-year solar periodicity – solar interior dynamics.

#X-class flares


Crosby et al., 1993

Frequency distributions of HXR flares

Power-law distribution offlare-related phenomena

Lu & Hamilton, 1991

Avalanche model of solar flares, does not expect any changes over the cycle

Dennis, 1985; Hudson, 1991

invariance of slope in the course of the solar cycle for HXR flare occurrence

Crosby et al., 1993; Lu et al., 1993


Veronig et al. 2002

cycle 23

cycle 22

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

the power-law index does not reveal any remarkable change in the course of the solar cycle

Christie et al., 2008

similar outcome for 6-12 keV frequency distribution (RHESSI data) during 2002-2006


SXR background flux (XBF) and Ri

Veronig et al. 2003

Delay of peak XBF for cycles 21, 23; no delay for cycle 22

Pearce, 1992; Wilson, 1993; Aschwanden, 1994;

GOES 1-8A flux (1975-2003)

Relation XBF and SN: power law

fit values differ 21, 23 - 22


North-south (N-S) asymmetry

Vizoso & Ballester, 1990; Li et al., 2009

Asymmetry most significant during solar minimum

N-S asymmetry changes every four cycles – hint of long-term periodic behavior of 8 cycles

N-S asymmetry is real; not due to random fluctuations

found for various kinds of solar activity indices, sunspots (Ri, areas, groups, magnetic classes, etc.), flares, prominences, radiobursts, hard X-ray bursts, gamma-ray bursts, CMEs

Temmer et al., 2001

Roy, 1977; Garcia, 1990; Joshi, 1995; Li et al. 1998; Atac & Özguc, 2001; Brajsa et al. 2005; Knaack et al. 2005; Carbonell, 2007; …

Carbonell et al., 1993


Temm

er et al., 2002

Garcia, 1990; Bai, 1987, 1988;

Northern hemisphere dominates soon after minimum; south at the end of the cycle

Li et al., 2009North-south (N-S) asymmetry

S

NN

S

S

N

Indication of 22-year alternationSwinson & Derek, 1986

Average rotational periods differ between northern and southern hemisphere

Hemispheres coupled weakly during the cycle

Temmer et al., 2002; Joshi et al. 2009

* triangles indicate solar max.


Coronal mass ejections

20-day sequence of SOHO/LASCO C3 observationsduring the high activity phase in Oct/Nov 2003.

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., 2004

Robbrecht, Berghmans, Van der Linden 2009

Data 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

CACTus 3.0 4.2 7.2 8.1 7.8 7.8 6.3 4.9 3.7 2.4 CDAW 1.1 3.1 3.4 4.6 4.3 4.7 3.3 3.2 3.5 3.1


Relation between CMEs and sunspot number


CME cycle lags sunspot cycle 23

For cycle 21-22 this effect was not clearly present

peculiarity of cycle 23?

Webb & Howard 1994

on average halo CMEs are less during minimum

projection effects (STEREO)


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


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


Coronal holes

driver of solar-terrestrial impacts

HSS during minimum activity

CIRs during decline phase

density net flux weakly correlated to the area of CHs

solar wind speed, Dst index , related to the area of CHs

Vrsnak, Temm

er, Veronig, 2007

.mov

Schwenn 1983; Crooker & Cliver 1994

Webb, 1995; Gopalswamy, 2005

Abramenko et al., 2009

Robbins et al., 2006; Vrsnak et al. 2007


solar activity during the past 70 years is exceptional (equally high activity more than 8,000 years ago)

Modern Maximum (1920 – ?)

grand minima/maxima are not a result of long-term cyclic variations but defined by stochastic/chaotic processesUsoskin et al., 2007

Abreu et al., 2008Solanki et al., 2004

end of grand maximum in solar magnetic activity within the next 2-3 solar cycles

How peculiar is this solar minimum?


2018

Sun

spot

rela

tive

num

ber (

Ri)

#consecutive days with Ri=0: 92


16

22#consec. days with Ri=0: 31


Pöt

zi, 2

009

Cumulative number of spotless days during a cycle

Solar cycle 23 is comparable to cycle 14 (ended 1913)

there is nothing peculiar about this minimum (not yet?)



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?

The end of high minima?


Conclusions

2) North-South asymmetry: real, indication of 22-year variation >> Important constraints from observations for solar dynamo models

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?

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?

statistical properties of flares/sunspots over the solar cycle€¦ · m. temmer: statistical...

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