Long term solar/heliospherc variability

Transcription

1 1 Long term solar/heliospherc variability Ilya Usoskin Sodankylä Geophysical Observatory, University of Oulu, Finland

2 Cosmic Ray variability at Earth 2 Cosmic Rays 1E+5 Geomagnetic field Local Interstellar spectrum Cut-off rigidity (GV) 1E+4 Diff. spectrum (GeV m2 sec ster)-1 IMF, solar wind NM count rate, cts/h/counter Solar minimum 1E+3 4 1E+2 35 Solar maximum 1E+1 3 Variable solar activity expands to the Heliosphere: solar wind, interplanetary magnetic field, 25 1E+ interplanetary transients (CME, corotation regions), etc. 2 1E-1 Galactic cosmic rays are modulated by IMF, magnetic inhomogeneities, solar wind; 15 1E Geomagnetic field partly shields the Earth (mid- andlatitude low-latitude Geomagnetic (deg) regions) from incoming Cosmic Ray energy (GeV/nucleon) cosmic rays

3 The heliosphere 3

4 solar cycle variations 4 11-year cycle due to solar activity Weak 22-year cycle due to charge-dependent drift effects short-term fluctuations. Centennial variability? sunspot numbers CR count rate (%) Climax, 3 GV 8 Huan/Hale, 13 GV

5 Solar activity changes 5 15 Modern Grand Maximum Group sunspot number 1 5 Maunder minimum Dalton minimum year solar cycle; Variable amplitude/envelope; Maunder minimum; The contemporary level is/was high;

6 Long-term CR 6 Model computations: SN -> open flux model (Solanki et al., 22; Krivova et al., 27); open flux -> CR (Usoskin et al., 25); CR -> 1 Be (Usoskin & Kovaltsov, 28) Sunspot number Nst, 1 5 cnts/h Be, 1 4 atom/g Greenland.4 Reconstruction -5.2 Antarctic Be, promille

7 Solar activity 7 Direct measurements Optical measurements Sunspot counts and drawings Aurora sightings Naked eye sunspot observations Cosmogenic isotopes 1E+6 1E+5 1E+4 1E+3 1E+2 1E+1 1E+ Years before present

8 Cosmogenic isotope production 8 Atmospheric cascade In the atmospheric cascade, nuclear reactions may take place, most important being: Spallation reactions on O, N, Ar 7 Be, 1 Be, 22 Na, 36 Cl, etc. Neutron capture: 14 N+n 14 C+p Storage in natural independetly dated archives: ice-cores, tree trunks, sediments, corals

9 14 C production by GCR and SCR 1E E+ Flux (GeV cm 2 ster sec) -1 1E-1 1E-2 1E-3 1E-4 1E-5 GCR, max 14 C production (cm 2 sec GeV) -1 1E-1 SCR, average SCR, E-2 GCR, min E (Gev/nucleon) 1E-3 Yield function (arb.units) 1 14C, Global 1 NM 1Be, polar E (GeV) 1E E (GeV/nucleon)

10 The approach: Scheme 1 Direct problem (Usoskin et al. 22) Sunspot numbers Model by Solanki et al. (2), Krivova et al. (27) Sunspot activity nonlinear. open solar magnetic flux through IMF strength Heliospheric parameters Heliospheric model (Usoskin et al., 22, 25) Open mag. flux nonlinear CR intensity variations cosmogenic isotopes in natural archives CR intensity 1 Be (Masarik & Beer, 1999; Webber & Higbie 23; Uoskin & Kovaltsov, 21) 14 C (Castagnoli & Lal, 198)

11 14C production: a model C production rate (at/cm 2 /sec) Φ (MV) M (1 25 G cm 3 ) Model: 14 C production function Castagnoli & Lal (198); Local interstellar spectrum Burger et al. (2); 1.5D cosmic ray transport in the heliosphere Usoskin et al. (22)

12 cosmogenic 14 C and 1 Be 12 n + N 14 C CO 2 carbon cycle tree rings Effective CR energy is ~ 3 GeV/nucleon; mean altitude: upper tropo, low stratosphere; measurements: normalized 14 C/ 12 C ratio CR + N,O 1 Be aerosols fall out Effective CR energy is 1 2 GeV/nucleon; mean altitude: upper tropo, lower stratosphere; measurements: abundance Cosmic Rays Atmosphere NO helio modulation geomagnetic Climate Cosmic Rays Stratosphere NO Troposphere Biosphere Ocean mixed layer Ocean deep layers Geosphere

13 Atmospheric transport of 1 Be 13 Annual Mean Wet 1 Be Precipitation- Field et al (JGR, 26)

14 Do we know Be transport? 14 2 SEP63 2 CAP USP Be concentration (1-15 ppmv) DEP NZP DOY AUP Modelling-vs-measurements of 7 Be (τ 1/2 =53 days) variations (Usoskin et al., 29) show good agreement BUT require nudging to the actual meteorological data.

15 Carbon cycle (Pandora model) 15

16 Carbon cycle: from Δ 14 C to Q 16 How to define Q from 14 C? Global mixing in the geosphere => little regional effects; assumption on stability of the carbon cycle (justified for Holocene);.1 Most important is the ocean ventilation; Suess effect Attenuation calibration to the modern epoch; 1.1 1E-5 1E-4 1E-3 1E-2 1E-1 Frequency (year -1 ) Knowledge of independently defined 9 geomagnetic field variations is required; (fossil fuel burning) => prevents direct Inversion method (Stuiver & Quay, 198; 3Usoskin & Kromer, 25) Phase shift (deg) 6 1E-5 1E-4 1E-3 1E-2 1E-1 Frequency (year -1 ) 14C (per mille) 14 C prod. rate (at/cm 2 /sec) Bode plots for the carbon cycle model Years (AD/BC)

17 Advantages and shortcomings advantages OFF-LINE type Primary archiving is done routinely in a similar manner throughout the ages. Measurements are done nowadays in laboratories. If necessary, all measurements can be repeated and improved. Absolute independent dating is possible (tree-rings, ice cores, marine sediments, etc.) As a result, a homogeneous, of equal quality, data series can obtained. 17 Shortcomings Redistribution in the geosphere and archiving may be affected by local and global climate/circulation processes which are to a large extend unknown in the past, thus justified only for the Holocene (since ca. 95 BC) 1 Be unknown mixing; prone to short-term regional and long-term global transport variability 14 C global mixing; changes of ocean circulation (multi-millennial scales); Suess effect; SOLUTION: Combined results from different nuclides, e.g. 1 Be and 14 C, whose responses to terrestrial effects are very different and may allow for disentangling external and terrestrial signals. Other proxy???

18 Solar activity throughout the Holocene Sunspot Number 1 5 Years BP a 18 SN errors Years AD/BC b c M (1 25 G cm 3 ) Solanki, Usoskin, Kromer et al., Nature, 24

19 Geomagnetic dipole moment 19 Dipole moment (1 22 Am 2 ) Y HBI K5 A Years (-BC/AD)

20 Geomagnetic field effect 2 1 Modulation potential (MV) Yang 2 ArcheoInt CALS7K

21 1 Be-vs- 14 C C (1 4 at g -1 ) C (arb. units) F (1 5 at cm -2 yr -1 ) C (1 4 at g -1 ) B) DF5 (Antarctica) D) Dye3 (Greenland) A) GISP (Greenland) C) South Pole Usoskin et al. (JGR, 29): 14 C and 1 Be data agree with each other (solar signal) at timescales 1-1 year; Agreement between 14 C and any 1 Be series is BETTER than between individual 1 Be series. Shorter time scale local climate in 1 Be data; Longer time scales global climate (delayed effect of deglaciation). 21

22 Ti-44 activity in meteorites: direct test 22 44Ti activity (dpm/ GSN S4 M5-A M5-M Ti-44 1Be-U Ti (τ 1/2 =6 yr) measured in stony meteorites direct test for CR reconstructions (Usoskin et al., A&A, 26). However, reconstruction from 44 Ti is impossible (time integration).

23 Reconstructed sunspot activity 23 8 Sunspot number Grand minima 19 Grand maxima can be identified: Minima (188 yr 17%) Maxima (13 yr 9%) 8 Sunspot number Years (-BC/AD) Solanki, S.K., I.G. Usoskin, B. Kromer, M. Schuessler, J. Beer, Nature, 24; Usoskin, Solanki & Kovaltsov, A&A, 27

24 How often do SEP events occur? 24 The probability of a SEP event to occur (after McCracken et al., 21; Hundson, 21)

25 Summary 25 The main source of CR variability on time scales from days to millennia is the solar magnetic activity. The dominant is 11-year solar cycle but there is essential centennial-millennial variability. CR variations, via cosmogenic isotopes, is the only source of information on the solar/heliospheric activity in the past. CR/solar variability can be reliably reconstructed for the Holocene (last 11 millennia) from cosmogenic isotope data. The level of solar/heliospheric activity varies between Grand minima and Grand maxima.

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