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The use of 17 GHz radio emission to characterize the solar minimum

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The use of 17 GHz radio emission to characterize the solar minimum. Selhorst, Caius L., Svalgaard, L., Giménez de Castro, C. G., Válio, A., Costa, J. E. R., Shibasaki, K. Ciclo solar XXIV. Alternative index.

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Presentation Transcript
slide1
The use of 17 GHz radio emission to

characterize the solar minimum

Selhorst, Caius L., Svalgaard, L.,

Giménez de Castro, C. G., Válio, A., Costa, J. E. R., Shibasaki, K.

slide3
Alternative index
  • Tlatov (2009) suggested to employ alternative index in the solar minimum periods.

# Polar faculae

# Sunpots

  • Sheeley (2008) pointed that the number of faculae in 2006 was smaller than that observed in previous minima.
slide4
Alternative index
  • Wang et al. (2009): polar magnetic field 40% smaller during this minimum in comparison with the previous cycle.
slide5
The Sun at 17 GHz

Nobeyama Radioheliograph

slide7
Solar radius

Selhorst et al. 2004

slide8
Solar radius

Selhorst et al. 2011

slide9
Polar limb brightening

Selhorst et al. 2010

slide10
The Sun at 17 GHz
  • Svalgaard & Cliver (2006): the bright patches are locations of strong magnetic fields.
slide11
Polar limb brightening

Selhorst et al. 2011

slide12
Polar limb brightening

Selhorst et al. 2010

  • Gyro-resonance emission at 17 GHz originates from the 3rd harmonic, i.e., ~2000 G (?);
  • Bremsstrahlung can produce the observed due to the heating of the local atmosphere.
slide13
Discussion
  • The results above show a remarkable decrease of the solar radius and polar limb brightening at 17 GHz during this unusual solar minimum.
  • It is necessary to take into account that measurement of the radius at 17 GHz may represent the mean emission of many small chromospheric features joined with the emission originating from sunspots/active regions. From this perspective, our results can be interpreted as a reduction in the activity related to the 17 GHz atmospheric.
  • Since the present analysis shows a clear reduction in the polar limb brightening intensities during the current minimum, the observed decreases in faculae number (Sheeley 2008) and polar magnetic field intensities (Wang et al. 2009) support the theory that the magnetic features are the origin of the limb brightening.
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