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In this work we take advantage of eleven different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are better fitted by different distributions (as has been reported previously in the literature). However, we find that all our databases can be reconciled by the simple application of a proportionality constant, and that, in reality, different databases are sampling different parts of a composite distribution. This composite distribution is made up by linear combination of Weibull and log-normal distributions -where a pure Weibull (log-normal) characterizes the distribution of structures with fluxes below (above) 10 21 Mx (10 22 Mx). We propose that this is evidence of two separate mechanisms giving rise to visible structures on the photosphere: one directly connected to the global component of the dynamo (and the generation of bipolar active regions), and the other with the small-scale component of the dynamo (and the fragmentation of magnetic structures due to their interaction with turbulent convection). Additionally, we demonstrate that the Weibull distribution shows the expected linear behaviour of a power-law distribution (when extended into smaller fluxes), making our results compatible with the results of Parnell et al. (2009).

Measurements from the Mount Wilson Observatory (MWO) are used to study the long-term variations of sunspot field strengths from 1920 to 1958. Following a modified approach similar to that in Pevtsov et al. (2011), for each observing week we select a single sunspot with the strongest field strength measured that week and then compute monthly averages of these weekly maximum field strengths. The data show the solar cycle variation of the peak field strengths with an amplitude of about 500-700 gauss (G), but no statistically significant long-term trends. Next, we use the sunspot observations from the Royal Greenwich Observatory (RGO) to establish a relationship between the sunspot areas and the sunspot field strengths for Cycles 15-19. This relationship is then used to create a proxy of peak magnetic field strength based on sunspot areas from the RGO and the USAF/NOAA network for the period from 1874 to early 2012. Over this interval, the magnetic field proxy shows a clear solar cycle variation with an amplitude of 500-700 G and a weaker long-term trend. From 1874 to around 1920, the mean value of magnetic field proxy increases by about 300-350 G, and, following a broad maximum in 1920-1960, it decreases by about 300 G. Using the proxy for the magnetic field strength as the reference, we scale the MWO field measurements to the measurements of the magnetic fields in Pevtsov et al. (2011) to construct a combined data set of maximum sunspot field strengths extending from 1920 to early 2012. This combined data set shows strong solar cycle variations and no significant long-term trend (linear fit to the data yields a slope of −0.2±0.8 G year −1 ). On the other hand, the peak sunspot field strengths observed at the minimum of the solar cycle show a gradual decline over the last three minima (corresponding to cycles 21-23) with a mean downward trend of ≈ 15 G year −1 .

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In this paper we discuss QPOs registered at microwaves using the Nobeyama Radioheliograph (NoRH). Our main conclusions concerning the QPO, found from NoRH observations, include: In addition to widely known 3-min oscillations and comparatively less investigated shorter fluctuations, we have registered over sunspots at microwave range also a diversity of more long-term periodic processes having typical periods of tens and hundreds of minutes. In some sunspots these periods are dominating. In a single active region, different plasma structures can simultaneously oscillate within a long-term range with different periods. Most of the different plasma structures of the solar atmosphere registered at the Nobeyama radio maps at a wavelength of 1.76 cm at all heliographic latitudes show the presence of the long-term QPO. In observations of the QPO at microwaves, we have dealt mostly with nonstationary processes. We have thus used wavelet analysis to estimate the quality of proper plasma resonators responsible for QPOs. In our interpretation, three types of plasma oscillators were proposed to be of importance: resonators that coincide with the emitting region; resonators that are outside, but close to the radio emitter; and resonators of the global solar nature. We conclude that NoRH has opened a new era in the study of different quasi-periodic oscillations and waves in the plasma structures of the solar atmosphere.

In this work a new information resource located at http://www.gao.spb.ru/database/esai and hereinafter referred to as ESAI ("Extended time series of Solar Activity Indices") is presented. ESAI includes observational, synthetic and simulated sets to study solar magnetic field variations and their influence on the Earth. ESAI extends the ordinary lengths of some traditional indices, parameterizing time variations of physically different characteristics of solar activity. In particular, long-term sets of the following indices are presented: sunspot areas, the Wolf numbers, polar faculae numbers, sunspot mean latitudes and north-south asymmetry of hemispheres for different components of activity. Some methods for making correct conclusions from incomplete data and some criteria to estimate the reliability of the obtained information are discussed.

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