Die wunderbare Welt der Sonnenzyklen

Allmonatlich geben Frank Bosse und Fritz Vahrenholt an dieser Stelle einen Überblick zur Entwicklung der Sonnenaktivität. Der Trend ist klar: Wir steuern auf ein tiefes solares Minimum zu. Die Satellitenmessungen zur sogenannten Total Solar Irradiance bilden eine wichtige Datenquelle. Vor drei Jahren sah es kurzfristig schwierig aus, als einige der um die Erde kreisenden Messgeräte langsam in die Jahre kamen und eine Datenlücke drohte. Zum Glück wurde dann doch noch schnell eine Lösung gefunden, um die Datenerfassung lückenlos weiterzuführen. Siehe Eos-Bericht hier.

Eines ist klar: Das solare Maximum, das die zweite Hälfte des 20. Jahrhunderts dominierte  – und vermutlich nicht ganz zufällig mit einem starken Schub der globalen Erwärmung zusammenfiel – ist auch im Kontext der letzten 10.000 Jahre ein besonders bedeutendes Maximum. Usoskin et al. 2014 rekonstruierten die solare Aktivität für die letzten 3000 Jahre und dokumentierten die kürzlich besonders kräftige Strahlkraft der Sonne.

Seit langem kennt man die verschieden Zyklen der Sonne, die sich zu einer Gesamtkurve überlagern. So pulsiert der Gleissbergzyklus im 90-Jahrestakt. Feynman & Ruzmaikin 2014 haben den Zyklus genauer beschrieben:

The Centennial Gleissberg Cycle and its association with extended minima
The recent extended minimum of solar and geomagnetic variability (XSM) mirrors the XSMs in the nineteenth and twentieth centuries: 1810–1830 and 1900–1910. Such extended minima also were evident in aurorae reported from 450 A.D. to 1450 A.D. This paper argues that these minima are consistent with minima of the Centennial Gleissberg Cycles (CGCs), a 90–100 year variation observed on the Sun, in the solar wind, at the Earth, and throughout the heliosphere. The occurrence of the recent XSM is consistent with the existence of the CGC as a quasiperiodic variation of the solar dynamo. Evidence of CGCs is provided by the multicentury sunspot record, by the almost 150 year record of indexes of geomagnetic activity (1868 to present), by 1000 years of observations of aurorae (from 450 to 1450 A.D.) and millennial records of radionuclides in ice cores. The aa index of geomagnetic activity carries information about the two components of the solar magnetic field (toroidal and poloidal), one driven by flares and coronal mass ejections (related to the toroidal field) and the other driven by corotating interaction regions in the solar wind (related to the poloidal field). These two components systematically vary in their intensity and relative phase giving us information about centennial changes of the sources of solar dynamo during the recent CGC over the last century. The dipole and quadrupole modes of the solar magnetic field changed in relative amplitude and phase; the quadrupole mode became more important as the XSM was approached. Some implications for the solar dynamo theory are discussed.

Ein weitere wichtiger solarer Zyklus ist der Suess-de Vries-Zyklus mit einer Periode von etwa 200 Jahren. Tlatov 2015 prognostiziert gemäß diesem Zyklus ein großes solares Minimum zwischen 2025-2035 heraufziehen:

The change of the solar cyclicity mode
Our analysis of groups of sunspots since the year 1610 till indicates that the Gnevyshev–Ohl rule (GO) displays cycles of inversion with the period of 200 years. The latest inversion occurred in the Hale double cycle 22–23. Due to that, in several subsequent double cycles the odd cycles should be weaker than their preceding even cycles. Gleissberg cycles with the period of about 100 years and variations with the period of 200 years are manifested in variations of physical parameters of sunspots and are interconnected. We suggested that the secular minima of the solar activity occur in the vicinity of the extreme points of the 200-year cycles of inversion of the GO rule. The peak of the next secular minimum is expected between the years 2025-2035. We studied the variations of the physical parameters of sunspots in a Gleissberg cycle. At the maximum phase of the Gleissberg cycle, the average area of groups and the average number of spots in a group reach their maximum. According to our forecast, the amplitude of the 25th solar activity cycle will be somewhat lower than that of the 24th.

Auf ein ähnliches Timing für das solare Minimum kommen auch Yndestad & Solheim 2017:

The influence of solar system oscillation on the variability of the total solar irradiance
Total solar irradiance (TSI) is the primary quantity of energy that is provided to the Earth. The properties of the TSI variability are critical for understanding the cause of the irradiation variability and its expected influence on climate variations. A deterministic property of TSI variability can provide information about future irradiation variability and expected long-term climate variation, whereas a non-deterministic variability can only explain the past.

This study of solar variability is based on an analysis of two TSI data series, one since 1700 A.D. and one since 1000 A.D.; a sunspot data series since 1610 A.D.; and a solar orbit data series from 1000 A.D. The study is based on a wavelet spectrum analysis. First, the TSI data series are transformed into a wavelet spectrum. Then, the wavelet spectrum is transformed into an autocorrelation spectrum to identify stationary, subharmonic and coincidence periods in the TSI variability.

The results indicate that the TSI and sunspot data series have periodic cycles that are correlated with the oscillations of the solar position relative to the barycenter of the solar system, which is controlled by gravity force variations from the large planets Jupiter, Saturn, Uranus and Neptune. A possible explanation for solar activity variations is forced oscillations between the large planets and the solar dynamo.

We find that a stationary component of the solar variability is controlled by the 12-year Jupiter period and the 84-year Uranus period with subharmonics. For TSI and sunspot variations, we find stationary periods related to the 84-year Uranus period. Deterministic models based on the stationary periods confirm the results through a close relation to known long solar minima since 1000 A.D. and suggest a modern maximum period from 1940 to 2015. The model computes a new Dalton-type sunspot minimum from approximately 2025 to 2050 and a new Dalton-type period TSI minimum from approximately 2040 to 2065.

Im März 2017 informierte das National Center for Atmospheric Research/University Corporation for Atmospheric Research über eine neue Entdeckung von der Sonne: Man hatte dort sogenannte Rossby-Wellen gefunden:

Planetary waves, first found on Earth, are discovered on Sun

Waves may influence space weather, offer a source of predictability

 The same kind of large-scale planetary waves that meander through the atmosphere high above Earth’s surface may also exist on the Sun, according to a new study led by a scientist at the National Center for Atmospheric Research (NCAR). Just as the large-scale waves that form on Earth, known as Rossby waves, influence local weather patterns, the waves discovered on the Sun may be intimately tied to solar activity, including the formation of sunspots, active regions, and the eruption of solar flares. “The discovery of magnetized Rossby waves on the Sun offers the tantalizing possibility that we can predict space weather much further in advance,” said NCAR scientist Scott McIntosh, lead author of the paper.

Weiterlesen beim NCAR/UCAR.

Ein etwas seltsamer Artikel erschien im Juli 2017 in Sky & Telelscope. Darin wird suggeriert, die aktuell nachlassende Sonnenaktivität könnte permanent sei, das Ende der Sonne einläuten. Was für ein Quatsch. Ganz hinten im Artikel wird dann eingeräumt, dass sich die solare Aktivität stets in Zyklen vollzogen hat.

Is Our Sun Slowing Down in Its Middle Age?

The Sun, now halfway through its life, might be slowing its magnetic activity, researchers say, which could lead to permanent changes in the sunspots and auroras we see.

The Sun has changed its figure, researchers say, and might keep it that way.

Weiterlesen in Sky & Telelscope