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Title: RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR

Abstract

Solar activity undergoes a variation over timescales of several months known as Rieger-type periodicity, which usually occurs near maxima of sunspot cycles. An early analysis showed that the periodicity appears only in some cycles and is absent in other cycles. But the appearance/absence during different cycles has not been explained. We performed a wavelet analysis of sunspot data from the Greenwich Royal Observatory and the Royal Observatory of Belgium during cycles 14–24. We found that the Rieger-type periods occur in all cycles, but they are cycle dependent: shorter periods occur during stronger cycles. Our analysis revealed a periodicity of 185–195 days during the weak cycles 14–15 and 24 and a periodicity of 155–165 days during the stronger cycles 16–23. We derived the dispersion relation of the spherical harmonics of the magnetic Rossby waves in the presence of differential rotation and a toroidal magnetic field in the dynamo layer near the base of the convection zone. This showed that the harmonics of fast Rossby waves with m = 1 and n = 4, where m ( n ) indicates the toroidal (poloidal) wavenumbers, perfectly fit with the observed periodicity. The variation of the toroidal field strength from weaker to stronger cyclesmore » may lead to the different periods found in those cycles, which explains the observed enigmatic feature of the Rieger-type periodicity. Finally, we used the observed periodicity to estimate the dynamo field strength during cycles 14–24. Our estimations suggest a field strength of ∼40 kG for the stronger cycles and ∼20 kG for the weaker cycles.« less

Authors:
; ; ; ;  [1]; ;  [2];  [3];  [4]
  1. Abastumani Astrophysical Observatory at Ilia State University, Tbilisi, Georgia (United States)
  2. Departament de Física, Universitat de les Illes Balears, E-07122, Palma de Mallorca (Spain)
  3. IGAM, Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz (Austria)
  4. Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001, Leuven (Belgium)
Publication Date:
OSTI Identifier:
22666048
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 826; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CONVECTION; DISPERSION RELATIONS; DISPERSIONS; LAYERS; MAGNETIC FIELDS; PERIODICITY; ROTATION; SOLAR CYCLE; SPHERICAL HARMONICS; SUN; SUNSPOTS

Citation Formats

Gurgenashvili, Eka, Zaqarashvili, Teimuraz V., Kukhianidze, Vasil, Ramishvili, Giorgi, Shergelashvili, Bidzina, Oliver, Ramon, Ballester, Jose Luis, Hanslmeier, Arnold, and Poedts, Stefaan. RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR. United States: N. p., 2016. Web. doi:10.3847/0004-637X/826/1/55.
Gurgenashvili, Eka, Zaqarashvili, Teimuraz V., Kukhianidze, Vasil, Ramishvili, Giorgi, Shergelashvili, Bidzina, Oliver, Ramon, Ballester, Jose Luis, Hanslmeier, Arnold, & Poedts, Stefaan. RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR. United States. https://doi.org/10.3847/0004-637X/826/1/55
Gurgenashvili, Eka, Zaqarashvili, Teimuraz V., Kukhianidze, Vasil, Ramishvili, Giorgi, Shergelashvili, Bidzina, Oliver, Ramon, Ballester, Jose Luis, Hanslmeier, Arnold, and Poedts, Stefaan. 2016. "RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR". United States. https://doi.org/10.3847/0004-637X/826/1/55.
@article{osti_22666048,
title = {RIEGER-TYPE PERIODICITY DURING SOLAR CYCLES 14–24: ESTIMATION OF DYNAMO MAGNETIC FIELD STRENGTH IN THE SOLAR INTERIOR},
author = {Gurgenashvili, Eka and Zaqarashvili, Teimuraz V. and Kukhianidze, Vasil and Ramishvili, Giorgi and Shergelashvili, Bidzina and Oliver, Ramon and Ballester, Jose Luis and Hanslmeier, Arnold and Poedts, Stefaan},
abstractNote = {Solar activity undergoes a variation over timescales of several months known as Rieger-type periodicity, which usually occurs near maxima of sunspot cycles. An early analysis showed that the periodicity appears only in some cycles and is absent in other cycles. But the appearance/absence during different cycles has not been explained. We performed a wavelet analysis of sunspot data from the Greenwich Royal Observatory and the Royal Observatory of Belgium during cycles 14–24. We found that the Rieger-type periods occur in all cycles, but they are cycle dependent: shorter periods occur during stronger cycles. Our analysis revealed a periodicity of 185–195 days during the weak cycles 14–15 and 24 and a periodicity of 155–165 days during the stronger cycles 16–23. We derived the dispersion relation of the spherical harmonics of the magnetic Rossby waves in the presence of differential rotation and a toroidal magnetic field in the dynamo layer near the base of the convection zone. This showed that the harmonics of fast Rossby waves with m = 1 and n = 4, where m ( n ) indicates the toroidal (poloidal) wavenumbers, perfectly fit with the observed periodicity. The variation of the toroidal field strength from weaker to stronger cycles may lead to the different periods found in those cycles, which explains the observed enigmatic feature of the Rieger-type periodicity. Finally, we used the observed periodicity to estimate the dynamo field strength during cycles 14–24. Our estimations suggest a field strength of ∼40 kG for the stronger cycles and ∼20 kG for the weaker cycles.},
doi = {10.3847/0004-637X/826/1/55},
url = {https://www.osti.gov/biblio/22666048}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 826,
place = {United States},
year = {Wed Jul 20 00:00:00 EDT 2016},
month = {Wed Jul 20 00:00:00 EDT 2016}
}