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Astron. Astrophys. 322, 311-319 (1997)

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2. Dataset used

To investigate the activity maximum shape during 11-year cycles, a set of four parameters related to different solar layers has been used. It is composed of:

1. the relative (or Zürich) sunspot number Rz (McKinnon 1987), updated with the international sunspot number (Solar Geophysical Data - Monthly Reports), as photospheric activity index. The analysis was restricted to the epoch 1849-1994 to avoid daily gaps existing prior to 1849;

2. the daily 10.7-cm ([FORMULA]) radio flux integrated on the whole solar disk, mainly as parameter of chromospheric activity (because of its sensitivity to the magnetic complexity of active regions; see: Wilson et al. 1987; Tapping & DeTracey 1990). Our dataset includes daily observations from February 14, 1947 to December 31, 1994 (Algonquin and Penticton radiotelescopes, Canada), corrected by the antenna gain, atmospheric absorption, burst in progress and the background sky temperature; moreover, each measurement is multiplied by the antenna efficiency ([FORMULA] = 0.9) and corrected by the variations in Sun-Earth distance;

3. the daily flux of the 1-8 [FORMULA] solar X-ray background, integrated on the whole solar disk, as a density parameter of the quiet corona structure. Data from the SOL ar RAD iation (SOLRAD) satellites cover the period March 14, 1968 - February 28, 1973 (i.e. the maximum phase of cycle 20; Solar Geophysical Data 1994a). Data from the G eostationary O perational E nvironmental S atellites (GOES) only cover the period January 1, 1987 - December 31, 1993 (the most part of cycle 22; Solar Geophysical Data 1994b), to avoid periods in which data have a high relative error induced by low-flux instrumental problems. Data for the maximum phase of cycle 21 are not available to us;

4. the monthly counts of grouped chromospheric flares from January, 1965 to December, 1994 (Solar Geophysical Data 1995; observations of the same event by different solar observatories were lumped together and counted as one). The released energy during flare events is connected to the presence of enhanced magnetic-field intensities in the involved regions.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998