Deciphering Solar Magnetic Activity: 140 Years of the ‘Extended Solar Cycle’ – Mapping the Hale Cycle

We investigate the occurrence of the “extended solar cycle” (ESC) as it occurs in a host of observational data spanning 140 years. Investigating coronal, chromospheric, photospheric, and interior diagnostics, we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) and previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder’s butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of $55^{\circ }$ 55 ∘ latitude in the evolution, and possible production, of solar magnetism.

Deciphering Solar Magnetic Activity: 140 Years Of The ‘Extended Solar Cycle’ – Mapping the Hale Cycle

We investigate the occurrence of the ``extended solar cycle'' (ESC) as it occurs in a host observational data spanning 140 years. Investigating coronal, chromospheric, photospheric and interior diagnostics we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) using previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder's butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55\degree\ latitude in the evolution, and possible production, of solar magnetism.

Impacts of sunspot number and Geomagnetic aa-index on climate of Wet Zone West Africa during solar cycles 22–24

Using the facilities at Heliophysics Science Division of NASA Goddard Space Flight Center, Greenbelt, MD, USA, we attempted to investigate the impact of solar magnetic activities on the climate of Wet Zone West Africa. The solar activity data namely, Sunspot Number (SSN) was obtained from the Royal Observatory of Belgium, Brussels; and Geomagnetic aa-index was obtained from World Data Center, Kyoto, Japan. Surface Air Temperature (SAT) and Rainfall data [for Port Harcourt in Nigeria and Abidjan in Cote D’Ivoire] were obtained from the HadCRUT-4 project of Climate Research Unit of University of East Anglia, United Kingdom. Firstly, we carried out Time Series Analysis of SSN and Geomagnetic aa-index spanning from 1950 to 2016. Secondly, we performed Regression Analysis on both solar activity data and climate variables to estimate the impact of solar magnetic activity on the Wet Zone West African climate. The Time Series Analysis showed that SSN variation was in-phase with Geomagnetic aa-index in all the solar cycles studied. Thus, Geomagnetic aa-index can be used as a proxy for studying solar magnetic activities. Performance of Regression Analysis showed that SSN regressed on SAT and Rainfall amounted to an average of 0.49 and 0.02% respectively throughout Solar Cycles 22–24. Furthermore, a regression of Geomagnetic aa-index on SAT and Rainfall yielded an average of 0.145 and 0.125% respectively. Our models showed that the variability of SAT and Rainfall in Wet Zone West Africa during Solar Cycles 22–24 are far less than 1%. Hence, the influence of SSN and Geomagnetic aa-index on SAT and Rainfall is less than 1%; and could cause ‘very small’ effect. These weak impacts are proofs that the variability of SAT and Rainfall were most probably not effected by SSN and Geomagnetic aa-index. Consequently, the variability of SAT and Rainfall in Wet Zone West Africa could not be attributed to SSN and Geomagnetic aa-index. We therefore, attempt to conclude that climate variability in Wet Zone West Africa is most probably not driven by solar magnetic activity, but could be attributed to anthropogenic activities.

Зависимость компоненты космического луча на фоне поверхности атмосферы от солнечной магнитной активности

Using Geant4 toolkit the changes of the flux density and of the dose rates of the secondary cosmic radiation at the heights up to 50 m from the land surface (at a depth of atmosphere about 1030 g/cm²) and depending on solar magnetic activity were estimated. For changes of Wolf’s number (sunspots) in the range of 0 — 200 the flux density of reflected from air and the soil g- and b- particles changes from 5.7 to 7 and 0.10 – 0.13 m-²s-¹ respectively, for energy from 0 keV to several units of GeV in the ground atmosphere on one meter from the earth. These estimates are much lower than those estimates, for radiation created by the soil and atmospheric radionuclides, which had been received earlier. In comparison with a contribution of radionuclides of the soil of flux density of secondary cosmic radiation about 0.01% and 0.1%, for gamma and beta radiation respectively. The received assessment of the dose rate transferred by secondary cosmic radiation about 0.7% from rate of the formed by soil’s radionuclides. In addition, an assessment of change in characteristics of secondary cosmic radiation depending on the level of solar magnetic activity presented in work. It is found that change of radiometric and dosimetric characteristics of secondary cosmic radiation depending on solar magnetic activity can be over 40%. It well repeats the changes of a dose found during a transcontinental flight. We found that the optimal average energy of spectrum of primary protons is 2.7 GeV. We can apply this feature to standards to find the most intensive periods of a secondary space gamma radiation and to use them in the experimental data, without involving the use of the Geant4. We have not found any significant contribution of secondary cosmic radiation reflected from the earth’s surface. This allows us to refuse from taking into account the soil layer in the model. С помощью инструментария Geant4 было произведено моделирование плотности потока и мощности дозы вторичного космического излучения на высотах до 50 м от поверхности земли (на глубине атмосферы около 1030 г/см²) и оценена их зависимость от солнечной магнитной активности. Для чисел Вольфа (количества пятен) в диапазоне от 0 до 200, плотность потока отраженных от воздуха и почвы g- и b-частиц изменялась от 5.7 до 7 и 0.10 — 0.13 м-²с-¹ соответственно для энергии от 0 кэВ до нескольких единиц ГэВ в приземной атмосфере на расстоянии одного метра от земли. Эти оценки намного ниже полученных ранее оценок для излучения, создаваемого почвенными и атмосферными радионуклидами. В сравнении с вкладом радионуклидов почвы в плотность потока, вклад вторичного космического излучения составляет около 0.01% и 0.1% для гамма- и бета-излучения соответственно. Полученная оценка мощности дозы, передаваемой вторичным космическим излучением, составляет около 0.7% от мощности дозы от радионуклидов из почвы. Кроме того, в работе представлена оценка изменения характеристик вторичного космического излучения в зависимости от уровня солнечной магнитной активности. Установлено, что изменение радиометрических и дозиметрических характеристик вторичного космического излучения в зависимости от солнечной магнитной активности может превышать 40%. Полученные результаты позволяют отказаться от учета слоя почвы в представленной модели.

Spatial distribution of quasi-biennial oscillations in high-latitude solar activity

ABSTRACT Quasi-biennial oscillations (QBOs) are considered to be a fundamental mode of solar magnetic activity at low latitudes (≤50°). However, the evolutionary aspect and the hemispheric distribution of solar QBOs at high latitudes (≥60°) are rarely studied. Here, we apply a relatively novel time-frequency analysis technique, called the synchrosqueezed wavelet transform, in order to extract the main components of the polar faculae in the Northern and Southern hemispheres for the time interval from 1951 August to 1998 December. We note the following. (i) Apart from the 22-yr Hale cycle, the 17-yr extended activity cycle and the 11-yr Schwabe cycle, QBOs have been estimated as a prominent time-scale of solar magnetic activity at high latitudes. (ii) The QBOs of the polar faculae are coherent in the two hemispheres, but the temporal (phase) and the spatial (amplitude) variations of solar QBOs occur unevenly on both hemispheres. (iii) For the 11-yr period mode, this begins in the Northern hemisphere three months earlier than in the Southern hemisphere. Moreover, the spatial and temporal distributions of the hemispheric QBOs differ from those of the 11-yr Schwabe cycle mode in the two hemispheres. Our findings could be helpful to improve our knowledge of the physical origin of the spatial distribution of solar QBOs at high latitudes, and could also provide more constraints on solar dynamo models introduced to characterize the different components of the solar magnetic activity cycle.

Solar-cycle irradiance variations over the last four billion years

Context. The variability of the spectral solar irradiance (SSI) over the course of the 11-year solar cycle is one of the manifestations of solar magnetic activity. There is strong evidence that the SSI variability has an effect on the Earth’s atmosphere. The faster rotation of the Sun in the past lead to a more vigorous action of solar dynamo and thus potentially to larger amplitude of the SSI variability on the timescale of the solar activity cycle. This could lead to a stronger response of the Earth’s atmosphere as well as other solar system planets’ atmospheres to the solar activity cycle. Aims. We calculate the amplitude of the SSI and total solar irradiance (TSI) variability over the course of the solar activity cycle as a function of solar age. Methods. We employed the relationship between the stellar magnetic activity and the age based on observations of solar twins. Using this relation, we reconstructed solar magnetic activity and the corresponding solar disk area coverages by magnetic features (i.e., spots and faculae) over the last four billion years. These disk coverages were then used to calculate the amplitude of the solar-cycle SSI variability as a function of wavelength and solar age. Results. Our calculations show that the young Sun was significantly more variable than the present Sun. The amplitude of the solar-cycle TSI variability of the 600 Myr old Sun was about ten times larger than that of the present Sun. Furthermore, the variability of the young Sun was spot-dominated (the Sun being brighter at the activity minimum than in the maximum), that is, the Sun was overall brighter at activity minima than at maxima. The amplitude of the TSI variability decreased with solar age until it reached a minimum value at 2.8 Gyr. After this point, the TSI variability is faculae-dominated (the Sun is brighter at the activity maximum) and its amplitude increases with age.

Stochastic Resonance could explain Recurrence of Grand Minima

<p>Proxies of solar activity have revealed repeated Grand Minima that occur with a certain regularity associated with the well-known Gleissberg and Süss/deVries cycles. These and other prominent cycles in the spectrum of solar activity are also seen in the spectrum of the planetary torque exerted on the solar tachocline, which has revived the hypothesis of a planetary influence on solar activity. It is not clear, however, how the extremely weak planetary forcing could influence the solar magnetic activity. Here, we suggest that stochastic resonance could explain the necessary amplification of the forcing and provide numerical evidence from stochastic time-delayed dynamo models. If the intrinsic noise of the solar dynamo allows for a frequent switching between active and quiescent stable states, tiny periodic forcings can be greatly amplified, provided the dynamo is poised close to a critical point. Such a forcing could be caused by a tidal modulation of the minimal magnetic field required for flux-tube buoyancy.</p>

Towards a more reliable reconstruction of the historical solar variability: a more realistic description of solar ephemeral magnetic regions

<p>Solar irradiance is a crucial input to climate models, but its measurements are only available since 1978. The variability of solar irradiance on climate-relevant time-scales is caused by the competition between bright and dark features formed by the magnetic fields emerging on the solar surface. Thus, models have been developed that reconstruct past irradiance variability from proxies of the solar magnetic activity. The longest direct proxy is the sunspot number. The common problem of such reconstructions is, however, that while sunspots adequately describe the evolution of the active regions (ARs) (large bipolar regions hosting sunspots), the evolution of their smaller counterparts, the ephemeral regions (ERs), is not directly featured by sunspots. At the same time, these small regions are much more numerous and are believed to be the main source of the long-term irradiance changes, which are of special interest to climate models. We develop an improved description of the ephemeral region emergence taking different solar observational constraints into account. The model builds on the SATIRE-T model, in which the emergence of ARs is described by the sunspot number and the emergence of the ERs is linearly linked to that of ARs. The latter, however, implies that whenever the sunspot number drops to zero, no magnetic field emerges in the model. In the new model, the emergence of the ERs is no longer linked to sunspots linearly. Instead, ARs and ERs are considered to be parts of a single power-law size distribution of the emerging magnetic regions. This ensures that even in the absence of ARs (e.g., during the grand minima of solar activity), the emergence rate of ERs remains non-zero. In particular, the solar open magnetic flux reconstructed using this approach does not drop to zero during the Maunder minimum, in agreement with independent reconstructions from the cosmogenic isotope data. Such an improved description of the ERs will allow a better constraint on the maximum solar irradiance drop during grand minima events. This, in turn, will allow a better constraint on the potential solar forcing in the future.</p>

Global simulations of stellar dynamos

The dynamo mechanism, responsible for the solar magnetic activity, is still an open problem in astrophysics. Different theories proposed to explain such phenomena have failed in reproducing the observational properties of the solar magnetism. Thus, ab-initio computational modeling of the convective dynamo in a spherical shell turns out as the best alternative to tackle this problem. In this work we review the efforts performed in global simulations over the past decades. Regarding the development and sustain of mean-flows, as well as mean magnetic field, we discuss the points of agreement and divergence between the different modeling strategies. Special attention is given to the implicit large-eddy simulations performed with the EULAG-MHD code.