Yu. A. Nagovitsyn

Solar Cyclicity during the Maunder Minimum

A multifaceted statistical study of all available data on solar activity during the Maunder minimum (1645–1715) is presented. The data include European telescope observations, Asian sunspot observations using the unaided eye, concentrations of cosmogeneous isotopes, and catalogues of polar aurorae. Joint analyses of data on the cosmogeneous isotopes 10Be and 14C are a promising source of information on solar activity in the past. The dates of relative sunspot maxima during the Maunder minimum are consistent with the idea that there were chaotic bursts of solar activity randomly distributed in time during this interval. The available evidence that the 11-year cyclicity was preserved in 1645–1715 are worthy of attention but require additional deep study and verification. No convincing evidence for a 22-year periodicity of the occurrence of sunspots during the Maunder minimum has been found.

Long-period oscillation processes in sunspot groups (ground-based and exoatmospheric observations)

The SOHO (MDI) exoatmospheric observations have proved the existence of long-period oscillations in active solar regions, which are manifested in a number of spatial and temporal modes; this had been established earlier by ground-based observations.

Eleven-year cyclicity of the sun on the 2000-year time scale

The paper describes the first reconstruction of the annual values of the total area and magnetic flux of sunspots, as well as the Wolf index, on the 2000-year time scale. The procedure was performed by combining data on solar cyclicity amplitudes obtained from a decadal reconstruction (Usoskin et al., 2014) and data on its phases acquired from the numbers of auroras, which is contained in catalogs by Křivský and Silverman.

The area and absolute magnetic flux of sunspots over the past 400 years

A new series of yearly-mean relative sunspot numbers SN2 that has been extrapolated into the past (to 1610) is presented. The Kislovodsk series with the scale factor b = 1.0094 ± 0.0059 represents a reasonable continuation of the mean-monthly and mean-yearly total sunspot areas of the Greenwich series after 1976. The second maximum of the 24th solar-activity cycle was not anomalously low, and was no lower than 6 of the past 13 cycles. A series A2 of values for the total sunspot area in 1610–2015 has been constructed, and is complementary to new versions of the series of the relative number of sunspots SN2 and the number of sunspot groups GN2. When needed, this series can be reduced to yield a quantity having a clear physical meaning—the spot absolute magnetic flux ΦΣ(t)[Mx] = 2.16 × 1019A(t) [mvh]. The maximum sunspot area during the Maunder minimum is much higher in the new series compared to the previous version. This at least partially supports the validity of arguments that cast doubt on the anomalously low ampltude of the solar cycles during the Maunder minimum that has been assumed by many researchers earlier.

Two populations of sunspots and secular variations of their characteristics

We investigate the magnetic fields and total areas of mid- and low-latitude sunspots based on observations at the Greenwich and Kislovodsk (sunspot areas) and Mount Wilson, Crimean, Pulkovo, Ural, IMIS, Ussuriysk, IZMIRAN, and Shemakha (magnetic fields) observatories. We show that the coefficients in the linear form of the dependence of the logarithm of the total sunspot area S on its maximum magnetic field H change with time. Two distinct populations of sunspots are identified using the twodimensional H–log S occurrence histogram: small and large, separated by the boundaries log S = 1.6 (S = 40 MSH) and H = 2050 G. Analysis of the sunspot magnetic flux also reveals the existence of two lognormally distributed populations with the mean boundary between them Φ = 1021 Mx. At the same time, the positions of the flux occurrence maxima for the populations change on a secular time scale: by factors of 4.5 and 1.15 for small and large sunspots, respectively. We have confirmed that the sunspots form two physically distinct populations and show that the properties of these populations change noticeably with time. This finding is consistent with the hypothesis about the existence of two magnetic field generation zones on the Sun within the framework of a spatially distributed dynamo.

Possible influence of climate factors on the reconstruction of the cosmogenic isotope 14C production rate in the earth’s atmosphere and solar activity in past epochs

The paper considers the probable influence of variations of the global temperature and carbon dioxide concentration in the Earth’s atmosphere on the results of reconstruction of the production rate of the cosmogenic isotope 14C in the terrestrial atmosphere for the period from the early 15th to the mid 19th century. This time interval covers the Spörer, Maunder, and Dalton minima of solar activity, as well as the Little Ice Age. It was shown that the climate changes that occurred during the Little Ice Age should be taken into account. In the Maunder and Spörer minima of solar activity, the 14C generation rate may be comparable to the values for the Dalton minimum, while exclusion of the climate effect yields extremely large values of the 14C production rate for these grand minima. In the solar activity reconstruction for past epochs, this circumstance should be taken into consideration via measurements of the 14C concentration on a long time scale.

Long-term variations of solar magnetic fields derived from geomagnetic data

There are limited homogeneous instrumental observations of the sunspot magnetic fields, but the Earth is a sort of a probe reacting to interplanetary disturbances which are manifestation of the solar magnetic fields. We find correlations between some parameters of geomagnetic activity (the geomagnetic activity “floor”—the minimum value under which the geomagnetic activity cannot fall in a sunspot cycle, and the rate of increase of the geomagnetic activity with increasing sunspot number), and sunspot magnetic fields (the sunspot magnetic field in the cycle minimum, and the rate of increase of the sunspot magnetic field from cycle minimum to cycle maximum). Based on these correlations we are able to reconstruct the sunspot magnetic fields in sunspot minima and maxima since sunspot cycle 9 (mid 19th century).Sunspots are dark spots on the solar surface associated with strong magnetic fields. The number, area, and brightness of sunspots are supposed to reflect the intensity of the solar magnetic fields and are often used as proxies for their long-term variations. However, the correlations between the sunspot parameters and solar magnetic fields are not constant, and the causes and the time profiles of the variations in these correlations are not quite clear. Therefore, the sunspot data alone cannot be used as proxy for deriving the variations of the sunspot magnetic fields for periods when no instrumental measurements are available. But the Earth is a sort of a probe reacting to interplanetary disturbances which are manifestation of the solar magnetic fields, so records of the geomagnetic activity can be used as diagnostic tools for reconstructing past solar magnetic fields evolution. In the present study we combine sunspot and geomagnetic data to estimate the long-term variations of sunspot magnetic fields.

Reconstructions of the heliospheric modulation potential and Wolf numbers based on the content of the 14C isotope in tree rings during the Maunder and Spörer minimums

Data on variations in the content of the 14C cosmogenic isotope in tree rings and the Earth’s atmosphere (Δ14C) make it possible to study the behavior of solar activity (SA) in previous centuries and millenniums. The latter is related to the fact that SA temporal variations result in a change in the IMF (Interplanetary Magnetic Field) parameters and, as a consequence, in the galactic cosmic ray (GCR) flux, under the action of which the 14C isotope is produced in the Earth’s atmosphere. This makes it possible to study SA history based on data on the 14C isotope content in tree rings. However, in this case we have several difficulties related to climate change. Climate changes result in carbon redistribution between natural reservoirs, which is reflected in radiocarbon data and results in solar signal distortion. The effect of variations in the global temperature and carbon dioxide concentration on the reconstruction of the heliospheric modulation potential and Wolf numbers from the late 14th century to the early 19th century is considered. It has been shown that the radiocarbon data do not make it possible to conclude that SA during the Maunder minimum was extremely low as compared to SA during the Dalton minimum.

Long-period variations in the magnetic field of small-scale solar structures

Thirty small-scale structures in the solar atmosphere, i.e., facula nodes at ±(20°–46°) latitudes, have been studied in order to analyze quasi-periodic variations in the magnetic field. SDO/HMI magnetograms have been used for this purpose. Long-period variations in the magnetic field strength of the considered objects in the 60–280 min range have been revealed as a result of data processing. It has been shown that there are no dependences between the magnetic field and period, nor between the magnetic field and object area. It has been assumed that the discovered variations are not natural oscillations of the magnetic field strength.

Analysis of quasi-periodic oscillations of position and brightness of details of the radio sources of the solar active regions based on observations made with the radio heliograph Nobeyama

As based on analysis of radio maps at the wavelength of 1.76 cm obtained from observations at the radio heliograph Nobeyama the parameters of oscillation processes in solar active regions were studied. As a technique for data processing wavelet analysis was used. The inherent periodicity in oscillations submits the existence of a resonance structure for some kinds of MHD waves in the plasma of the solar atmosphere. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html