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The latest SOHO VIRGO total solar irradiance (TSI) time series is analyzed using new solar variability measures obtained from full-disk solar images made at the San Fernando Observatory and the Mg II 280 nm index. We discuss the importance of solar cycle 23 as a magnetically simpler cycle and a variant from recent cycles. Our results show the continuing improvement in TSI measurements and surrogates containing information necessary to account for irradiance variability. Use of the best surrogate for irradiance variability due to photospheric features (sunspots and faculae) and chromospheric features (plages and bright network) allows fitting the TSI record to within an rms difference of 130 ppm for the period 1986 to the present. Observations show that the strength of the TSI cycle did not change significantly despite the decrease in sunspot activity in cycle 23 relative to cycle 22. This points to the difficulty of modeling TSI back to times when only sunspot observations were available.

NSO/Kitt Peak synoptic charts of magnetic flux in the period from 1996 to 1998 are analyzed together with time series for the 10.7 cm radio flux, sunspot number, and Mg II chromospheric index to determine the origin of the two times of minimum activity in 1996 and to study their relationships in the ascending phase of solar cycle 23. The solar activity minima in February-April and September-November of 1996 are found to correspond to periods of low magnetic activity in the southern and northern solar hemispheres, respectively. The new solar cycle becomes dominant in early 1997, but it is only in the summer of 1997 that a significant increase can be detected in the magnetic fields observations as well as in irradiance data, and by the end of 1998, the activity level has increased to a value comparable to the one observed in 1993. Using the magnetic synoptic charts, we determine the number of persistent longitude bands of active nests during this rising phase of solar cycle 23. We find an increase in the number of active nests from zero in 1996 to three by 1998. We speculate that these persistent bands of flux emergence correspond to a pattern of low-order modes of instability of the type found in the theoretical work of Gilman, Fox, and Dikpati on joint instability of latitudinal differential rotation and toroidal magnetic fields at the base of the convection zone. We argue that the observed increase in the number of active nests is consistent with the increase in the longitudinal wavenumber of magnetic instabilities in a concentrated toroidal field in the tachocline discussed in 1999 by Gilman and Dikpati.

In this paper we study interplanetary (IP) Ly? data taken with the Voyager1and Voyager2spacecraft from 1980 to 1995. The coverage in time is equal to about 156 and 220 points yr-1for Voyager1and Voyager2, respectively, with almost no gaps. The IP Ly? data are normalized for spatial changes in the emissivity, which arise from variations in observing geometry, by using a radiative transfer model. The normalized data show the variation of the solar H Ly? line-center flux during the solar cycle. We compare this variation with the solar H Ly? irradiance measurements of integrated flux from the SolarMesosphereExplorerand the UpperAtmosphereResearchSatellite/Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), and, when direct solar measurements are not available, we use estimated irradiances from magnesium and helium indices. The comparison between VoyagerIP data and solar data shows that the best agreement is found with the SOLSTICE set of measurements, when no differences in the variation of the line-center flux and the integrated flux are taken into account.