A Millennium Scale Sunspot Number Reconstruction: Evidence For an Unusually Active Sun Since the 1940's

The extension of the sunspot number series backward in time is of considerable interest for dynamo theory, solar, stellar, and climate research. We have used records of the Be-10 concentration in polar ice to reconstruct the average sunspot activity level for the period between the year 850 to the pr esent. Our method uses physical models for processes connecting the Be-10 concentration with the sunspot number. The reconstruction shows reliably that the period of high solar activity during the last 60 years is unique throughout the past 1150 years. This nearly triples the time interval for which such a statement could be made previouslyComment: 4 pages, LaTeX, revtex4 macros; Phys. Rev. Let., in pres

Energetic particle influence on the Earth's atmosphere

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere

A history of solar activity over millennia

Abstract Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes ¹⁴C and ¹⁰Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed

A history of solar activity over millennia

Abstract Here we review present knowledge of the long-term behaviour of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the dedicated indices used to quantify different aspects of variable solar activity, with special emphasis on sunspot numbers. Over long timescales, quantitative information about past solar activity is historically obtained using a method based on indirect proxies, such as cosmogenic isotopes ¹⁴C and ¹⁰Be in natural stratified archives (e.g., tree rings or ice cores). We give a historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state of the art. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that the method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene (the past ∼12 millennia). A separate section is devoted to reconstructions of extremely rare solar eruptive events in the past, based on both cosmogenic-proxy data in terrestrial and lunar natural archives, as well as statistics of sun-like stars. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed

Robustness of solar-cycle empirical rules across different series including an updated active-day fraction (ADF) sunspot group series

Abstract Empirical rules of solar-cycle evolution form important observational constraints for the solar-dynamo theory. This includes the Waldmeier rule relating the magnitude of a solar cycle to the length of its ascending phase, and the Gnevyshev–Ohl rule clustering cycles to pairs of an even-numbered cycle followed by a stronger odd-numbered cycle. These rules were established as based on the “classical” Wolf sunspot number series, which has been essentially revisited recently, with several revised sets released by the research community. Here we test the robustness of these empirical rules for different sunspot (group) series for the period 1749 – 1996, using four classical and revised international sunspot-number and group sunspot-number series. We also provide an update of the sunspot-group series based on the active-day fraction (ADF) method, using the new database of solar observations. We show that the Waldmeier rule is robust and independent of the exact sunspot (group) series: its classical and n+1 (relating the length of nth cycle to the magnitude of (n+1)th cycle) formulations are significant or highly significant for all series, while its simplified formulation (relating the magnitude of a cycle to its full length) is insignificant for all series. The Gnevyshev–Ohl rule was found robust for all analyzed series for Solar Cycles 8 – 21, but unstable across the Dalton minimum and before it

The energetic particle intensity estimated from cosmogenic isotope Al-26 produced in lunar samples

Abstract Direct measurements of solar energetic particles (SEP) became possible only in the space era covering past several decades. However, for many academic and practical reasons, it is important to know the SEP energy spectrum on much longer time scales in the past. Such information can be obtained using reconstructions based on cosmogenic radioisotope measurements in extra-terrestrial objects without magnetic and atmospheric shielding such as lunar surface or meteoroids. Thanks to the Apollo missions, samples of lunar rocks have been brought to the Earth and measured for the isotope content. Although estimates of the average SEP energy spectrum from cosmogenic radionuclides measured in lunar samples have been made earlier, here we revisit the approach using newly calculated depth profile of the yield function for ²⁶Al in lunar rocks. We have developed a full Monte-Carlo model of the nuclide production by energetic particles in the rock. As a result, we present the improved estimate of the average solar energetic particle intensity at 1 AU on the multi-millenial time scales

Role of heavier-than-proton nuclei in neutron monitor response

Abstract Heavier-than-proton nuclei in cosmic rays are responsible for up to 45% of neutron monitor (NM)response depending on the level of solar modulation as well as the geomagnetic rigidity cutoffand altitude of a given NM location. Therefore, careful consideration of these heavy species isimportant for an accurate analysis of NM data, including a reconstruction of the solar modulationpotential using the worldwide NM network data. Recently, the AMS-02 experiment allowed usto directly verify the NM response to heavy particles. In this work, we evaluate the expectedcontribution of heavy nuclei into the NM response considering different models of the localinterstellar spectrum and also for different levels of solar activity

A solar cycle of cosmic ray fluxes for 2006–2014:comparison between PAMELA and neutron monitors

Abstract A comparison of cosmic proton spectra directly measured by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment during 2006–2014 with data of polar neutron monitors for the same time interval is presented. It is shown that the measured spectra are well described by the force-field model for the modulation potential range 350–750 MV. The obtained modulation potential agrees with that calculated from the data of the world neutron monitor network for low solar activity between 2006 and 2012 but diverges during the maximum of solar cycle. The empirical relation between the modulation potential and the (inverted) neutron monitor count rate appears somewhat steeper than the modeled one, as confirmed also by data from fragmentary balloon-borne measurements. A reason for the discrepancy is unclear and calls for additional study using independent data sets

Spectra of solar energetic particles and galactic cosmic rays over a million years reconstructed using aluminium-26 data from lunar rocks

Abstract Direct measurements of solar energetic particles (SEP) cover the space era of several decades, but indirectly they can be studied for thousands and millions of years backward using cosmogenic nuclides in lunar rocks and soil. With a proper nuclide production model, it is possible to estimate the mean energy spectrum of SEP, as well as of galactic cosmic rays (GCR) from a depth profile of the measured nuclide content. Here we used aluminium-26 (lifetime 1.03 Myr) measurements in Apollo-mission lunar samples. Previous estimates of the SEP spectrum from lunar data were based on the assumed specific shape and only provided reconstructed spectral parameters. We report a different approach to use a lunar rock as an integral spectrometer within 20–80 MeV. With that, one can reconstruct the particle spectrum directly without any a-priori assumptions on its exact shape. For each studied lunar sample, we have developed an accurate Geant4 model. We estimated the average GCR spectrum over the last million years (the modulation potential 496±40 MV), which is consistent with that for the Holocene (449±70 MV), but significantly lower than that for the modern epoch (660±20MV).We also made a true reconstruction of the mean SEP spectrum over the last million years. The integral flux >30 MeV was estimated as 37.4 particles/(cm² s), which is consistent with that for the modern epoch. The estimated occurrence probability of SEP events shows no expected events with fluence >30 MeV over 5×10¹⁰ and 1×10¹¹ particles/cm² on millennial and Mega-year time scales, respectively

Effective energy of cosmogenic isotope (¹⁰Be, ¹⁴C and ³⁶Cl) production by solar energetic particles and galactic cosmic rays

Abstract Cosmogenic isotopes ¹⁴C, ¹⁰Be and ³⁶Cl measured in datable natural archives provide the only known quantitative proxy for cosmic-ray (CR) and solar-activity variability before the era of direct measurements. Studies of relations between the measured isotope concentrations and CR variability require complicated modeling including the isotope production and transport in the terrestrial system. Here we propose a rough “effective energy” method to make quick estimates of the CR variability directly from the cosmogenic data using an approximate linear scaling between the measured isotope concentrations and the energy-integrated flux of CR above the effective energy. The method is based on the thoroughly computed effective yield function presented here. A simple way to account for the variable geomagnetic field is also provided. The method was developed for both solar energetic particles (SEPs) and galactic cosmic ray (GCR) variability and is shown to provide a robust result within 20% and 1% accuracy, respectively, without an assumption of the specific spectral shape. Applications of the effective-energy method to the known extreme SEP events and the secular GCR variability are discussed. The new method provides a simple and quick tool to assess the CR variability in the past. On the other hand, it does not supersede the full detailed modeling required for precise results