Erich Rieger
CitizenshipGermany
Alma materPh.D. (Technical University of Munich)[1]
Known forRieger periodicities
Scientific career
FieldsAstrophysics, Heliophysics, Geophysics
InstitutionsMax Planck Institute for Extraterrestrial Physics
(Garching, Germany)
ThesisInterpretation of the sintering processes in thorium powder compacts (1962)

Erich Otto Ernst Rieger (born 1935 in Würzburg, Germany) is a German astrophysicist who spent his research career at the Max Planck Institute for Extraterrestrial Physics (MPE) near Munich. He is notable for his 1984 discovery of the period of ~154 days in solar flares. Since the discovery, the period has been confirmed in most heliophysics data in the Solar System, including the interplanetary magnetic field, and has become known as the Rieger period (PR).

Rieger periodicities

Rieger period

Rieger and coworkers discovered in 1984 a strong period of ~154 days in hard solar flares, at least since the solar cycle 19.[2] The period has since been confirmed in most heliophysics data and the interplanetary magnetic field, and is commonly known as the Rieger period.[3]

Rieger-type periodicities

Besides numerous confirmations of PR, its resonance harmonics were reported as well, including 5⁄6PR, 2⁄3PR, 1⁄2PR, 1⁄3PR, and 1⁄5PR, i.e., ~128, ~102, ~78, ~51, and ~31 days, called Rieger-type periodicities.[4] Types of data periodic with Rieger cycles include solar flares, photospheric magnetic flux, group sunspot numbers, and proton speed. Various longer (1–2 years) modulations also were reported in almost all heliophysics data types. Besides the above mentioned, data types that exhibit long-periodic dynamics include solar flare index, solar radio flux, and others, except for the coronal index and 10.7 cm solar flux.[5]

So far, these periodicities have been reported in different ranges, depending on data, location, epoch, and methodology, as 155–160 days, 160–165 days, 175–188 days, and 180–190 days.[6] Most of those studies indicate a leading periodicity ranging from 152 to 158 days, which appears to be dominant particularly in the time phase from ~1979–1983, corresponding to the solar maximum activity.[7]

Origin of Rieger resonance

Various proposals exist as to the origin of the underlying resonant process behind PR in the dynamics of Sun-ejected particles and its modulations and harmonics, including possible influences of planetary constellations on the Sun.[8][9] One such report found that a damped periodically forced nonlinear oscillator, which exhibits both periodic and chaotic behavior, can simulate the process described by Rieger periodicities.[10] The entire Rieger resonance was detected in the interplanetary magnetic field as well, including Earth's vicinity.[11]

Other work

High-energy solar flares

In 1989, Rieger provided strong evidence that flares with emissions >10 MeV are visible only near the solar limb.[12] Gamma-ray-emitting flares are observed from sites located predominantly near the limb of the Sun; this effect was observed for flares detected at energies >0.3 MeV, but it is at energies >10 MeV that the effect is particularly pronounced.[13] Since in both of these cases the bulk of the emission is bremsstrahlung from primary electrons, these results imply that the radiating electrons are anisotropic. Thus, the anisotropy could result from the mirroring of the charged particles in the convergent chromospheric magnetic fields.

The emissions are strongly anisotropic, with more emission in the directions tangential to the photosphere than in directions away from the Sun.[14] In order to account for the anisotropy of the gamma-ray emission from high energy solar flares, invoked are electron transport in the coronal region and magnetic mirroring of converging magnetic flux tubes beneath the solar transition region. As the gaseous models of the Sun cannot support the existence of a real surface, another mechanism must act as a surface.

Artificial comet

Rieger was involved in the MPE early research initiatives, including the first artificial comet, created by a cloud of barium ions, and which was released by the German IRM (Ion Release Module) satellite in 1985.[15]

References

  1. ↑ "Erich Rieger". Retrieved 25 November 2021.
  2. ↑ Rieger, E.; Share, G. H.; Forrest, D. J.; Kanbach, G.; Reppin, C.; Chupp, E. L. (1984). "A 154-day periodicity in the occurrence of hard solar flares?". Nature. Springer Science and Business Media LLC. 312 (5995): 623–625. Bibcode:1984Natur.312..623R. doi:10.1038/312623a0. ISSN 0028-0836. S2CID 4348672.
  3. ↑ Chowdhury, Partha; Khan, Manoranjan; Ray, P.C. (8 January 2009). "Intermediate-term periodicities in sunspot areas during solar cycles 22 and 23". Monthly Notices of the Royal Astronomical Society. Oxford University Press (OUP). 392 (1): 1159–1180. Bibcode:2009MNRAS.392.1159C. doi:10.1111/j.1365-2966.2008.14117.x. ISSN 0035-8711. S2CID 121248083.
  4. ↑ Dimitropoulou, Michaila; Moussas, Xenophon; Strintzi, Dafni (2008). "Enhanced Rieger type periodicities' detection in X-ray solar flares and statistical validation of Rossby waves' existence". Proceedings of the International Astronomical Union. Cambridge University Press (CUP). 4 (S257): 159–163. doi:10.1017/s1743921309029226. ISSN 1743-9213. S2CID 122570191.
  5. ↑ Forgacs-Dajka, E.; Borkovits, T. (1 January 2007). "Searching for mid-term variations in different aspects of solar activity - looking for probable common origins and studying temporal variations of magnetic polarities". Monthly Notices of the Royal Astronomical Society. Oxford University Press (OUP). 374 (1): 282–291. Bibcode:2007MNRAS.374..282F. doi:10.1111/j.1365-2966.2006.11167.x. ISSN 0035-8711.
  6. ↑ Gurgenashvili, Eka; Zaqarashvili, Teimuraz V.; Kukhianidze, Vasil; Oliver, Ramon; Ballester, Jose Luis; Dikpati, Mausumi; McIntosh, Scott W. (18 August 2017). "North–South Asymmetry in Rieger-type Periodicity during Solar Cycles 19–23". The Astrophysical Journal. American Astronomical Society. 845 (2): 137. arXiv:1707.08615. Bibcode:2017ApJ...845..137G. doi:10.3847/1538-4357/aa830a. ISSN 1538-4357. S2CID 118807885.
  7. ↑ Chowdhury, Partha; Kudela, K.; Moon, Y.-J. (7 January 2016). "A Study of Heliospheric Modulation and Periodicities of Galactic Cosmic Rays During Cycle 24". Solar Physics. Springer Science and Business Media LLC. 291 (2): 581–602. Bibcode:2016SoPh..291..581C. doi:10.1007/s11207-015-0832-7. ISSN 0038-0938. S2CID 124226330.
  8. ↑ Kurochkin, N. E. (1998). "Transient periodicity in solar activity". Astronomical & Astrophysical Transactions. Informa UK Limited. 15 (1–4): 277–279. Bibcode:1998A&AT...15..277K. doi:10.1080/10556799808201781. ISSN 1055-6796.
  9. ↑ Abreu, J. A.; Beer, J.; Ferriz-Mas, A.; McCracken, K. G.; Steinhilber, F. (28 November 2012). "Is there a planetary influence on solar activity?". Astronomy & Astrophysics. EDP Sciences. 548: A88. Bibcode:2012A&A...548A..88A. doi:10.1051/0004-6361/201219997. ISSN 0004-6361.
  10. ↑ Bai, Taeil; Cliver, E. W. (1990). "A 154 day periodicity in the occurrence rate of proton flares". The Astrophysical Journal. American Astronomical Society. 363: 299. Bibcode:1990ApJ...363..299B. doi:10.1086/169342. ISSN 0004-637X.
  11. ↑ Cane, H. V.; Richardson, I. G.; von Rosenvinge, T. T. (15 December 1998). "Interplanetary magnetic field periodicity of ~153 days". Geophysical Research Letters. American Geophysical Union (AGU). 25 (24): 4437–4440. Bibcode:1998GeoRL..25.4437C. doi:10.1029/1998gl900208. ISSN 0094-8276. S2CID 121571473.
  12. ↑ Vilmer, Nicole (13 July 2012). "Solar flares and energetic particles". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. The Royal Society. 370 (1970): 3241–3268. Bibcode:2012RSPTA.370.3241V. doi:10.1098/rsta.2012.0104. ISSN 1364-503X. PMID 22665901. S2CID 9212696.
  13. ↑ Ramaty, R., Simnett, G. M. (1991) Accelerated particles in solar flares. In: Sonett, C. P., Giampapa, M. S., Matthews, M. S. (Eds.) The Sun in Time, The University of Arizona Press, Tucson, AZ, pp. 232–259.
  14. ↑ Miller, James A.; Ramaty, Reuven (1989). "Relativistic electron transport and bremsstrahlung production in solar flares". The Astrophysical Journal. American Astronomical Society. 344: 973. Bibcode:1989ApJ...344..973M. doi:10.1086/167865. ISSN 0004-637X.
  15. ↑ Rieger, E. (2013) Explosive rocket men. In: Reflections on 50 years of extraterrestrial research, 1963–2013. Monograph on the occasion of the golden jubilee of the Max Planck Institute for Extraterrestrial Physics, pp. 18–21.

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