Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jgr...10019851s&link_type=abstract
Journal of Geophysical Research, Volume 100, Issue A10, p. 19851-19864
Astronomy and Astrophysics
Astrophysics
6
Solar Physics, Astrophysics, And Astronomy: Radio Emissions, And Astronomy: Solar Activity Cycle, And Astronomy: Solar Irradiance, And Astronomy: Solar And Stellar Variability
Scientific paper
The microwave flux of the Sun is responsive to the same conditions that produce magnetically structured radiation at visible and X ray wavelengths, and so the solar flux at high radio frequencies such as 2800 MHz (10.7 cm) has been used as a proxy for solar optical variations. We have previously found that the microwave flux time series show spectral variations that provide useful proxy information for total irradiance, and we have extended our analysis of the daily solar fluxes from Toyokawa Observatory at 1000, 2000, 3750, and 9400 MHz, in addition to the Ottawa 2800-MHz flux, for the years 1980-1989. An essential ingredient in our analysis is the extraction of the rotationally-modulated microwave component, which differs from the ``S component'' as recently defined in the literature. The rotationally-modulated fraction of the emission contains a significant, often dominant, contribution from gyroresonance emission, whereas the S component, as defined by the excess above the cycle minimum level, usually does not.
This allows us to distinguish plage-associated emission from spot-associated emission in the time series of microwave flux. We show that in combination, the microwave fluxes for 1000-9400 MHz, which span the spectral peak of spot-associated emission, provide a very good proxy both the active cavity radiometer irradiance monitor (ACRIM) total irradiance and the sunspot-blocked component of the irradiance, even without optical sunspot observations. Over the 1984-1989 period, this proxy has a weighted correlation with ACRIM of 95%, and an RMS deviation from the total irradiance of 0.27 w/m2, slightly better than the deviation (0.35 w/m2) found using optical data.
Kundu Mukul R.
Schmahl Ed. J.
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