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  1. No Access

    Article

    A Test of the Active-Day Fraction Method of Sunspot Group Number Calibration: Dependence on the Level of Solar Activity

    The method of active-day fraction (ADF) was proposed recently to calibrate different solar observers to standard observational conditions. The result of the calibration may depend on the overall level of solar...

    T. Willamo, I. G. Usoskin, G. A. Kovaltsov in Solar Physics (2018)

  2. No Access

    Article

    An Optical Atmospheric Phenomenon Observed in 1670 over the City of Astrakhan Was Not a Mid-Latitude Aurora

    It has recently been claimed (Zolotova and Ponyavin Solar Phys., 291, 2869, 2016; ZP16 henceforth) that a mid-latitude optical phenomenon, which took place over the city of Astrakhan in July 1670, according to Ru...

    I. G. Usoskin, G. A. Kovaltsov, L. N. Mishina, D. D. Sokoloff, J. Vaquero in Solar Physics (2016)

  3. No Access

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    Dependence of the Sunspot-Group Size on the Level of Solar Activity and its Influence on the Calibration of Solar Observers

    We study the distribution of the sunspot-group size (area) and its dependence on the level of solar activity. We show that the fraction of small groups is not constant but decreases with the level of solar act...

    I. G. Usoskin, G. A. Kovaltsov, T. Chatzistergos in Solar Physics (2016)

  4. No Access

    Article

    A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions

    Although sunspot-number series have existed since the mid-nineteenth century, they are still the subject of intense debate, with the largest uncertainty being related to the “calibration” of the visual acuity ...

    I. G. Usoskin, G. A. Kovaltsov, M. Lockwood, K. Mursula, M. Owens… in Solar Physics (2016)

  5. No Access

    Article

    Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected

    The amplitude of the 11-year cycle measured in the cosmogenic isotope 10Be during the Maunder Minimum is comparable to that during the recent epoch of high solar activity. Because of the virtual absence of the cy...

    S. V. Poluianov, I. G. Usoskin, G. A. Kovaltsov in Solar Physics (2014)

  6. No Access

    Article

    Fluence Ordering of Solar Energetic Proton Events Using Cosmogenic Radionuclide Data

    While data on the cosmogenic isotopes 14C and 10Be made it possible to evaluate extreme solar proton events (SPEs) in the past, their relation to standard parameters quantifying the SPE strengths, viz. the integr...

    G. A. Kovaltsov, I. G. Usoskin, E. W. Cliver, W. F. Dietrich, A. J. Tylka in Solar Physics (2014)

  7. No Access

    Article

    Occurrence Probability of Large Solar Energetic Particle Events: Assessment from Data on Cosmogenic Radionuclides in Lunar Rocks

    We revisited assessments of the occurrence probability distribution of large events in solar energetic particles (SEP), based on measurements of cosmogenic radionuclides in lunar rocks. We present a combined c...

    G. A. Kovaltsov, I. G. Usoskin in Solar Physics (2014)

  8. No Access

    Article

    Critical Comment on the Article by R. Rek “The Maunder Minimum and the Sun as the Possible Source of Particles Creating Increased Abundance of the 14C Carbon Isotope”

    Several strong but erroneous statements were made by R. Rek in an article published in this volume of Solar Physics. Here we show that these misleading statements are caused by neglecting the known effects of the...

    I. G. Usoskin, G. A. Kovaltsov in Solar Physics (2010)

  9. No Access

    Article

    Global Heliospheric Parameters and Cosmic-Ray Modulation: An Empirical Relation for the Last Decades

    We study empirical relations between the modulation of galactic cosmic rays quantified in terms of the modulation potential and the following global heliospheric parameters: the open solar magnetic flux, the t...

    K. Alanko-Huotari, K. Mursula, I. G. Usoskin, G. A. Kovaltsov in Solar Physics (2006)

  10. No Access

    Article

    Adiabatic Deceleration Effects on the Formation of Heavy Ion Charge Spectra in Interplanetary Space

    We investigate the effects of interplanetary propagation on the energy dependence of the mean ionic charge of ~0.1–1 MeV/n iron observed during impulsive solar particle events at 1 AU. A Monte-Carlo approach i...

    J. J. Kartavykh, W. DrÖge, G. A. Kovaltsov, V. M. Ostryakov in Solar Physics (2005)

  11. No Access

    Article

    Long-Term Solar Activity: Direct and Indirect Study

    The series of directly observed sunspot numbers is nearly 400 years long. We stress that the recently compiled group sunspot number series is an upgrade of the old Wolf series and should always be used before ...

    I. G. Usoskin, G. A. Kovaltsov in Solar Physics (2004)

  12. No Access

    Article

    An Upper Limit on Sunspot Activity During the Maunder Minimum

    We have estimated the upper and lower limits of sunspot activity, in terms of active day fraction during the Maunder minimum (1645–1710), using raw information on individual daily observations (Hoyt and Schatt...

    G. A. Kovaltsov, I. G. Usoskin, K. Mursula in Solar Physics (2004)

  13. No Access

    Article

    Reconstruction of Monthly and Yearly Group Sunspot Numbers From Sparse Daily Observations

    Some periods before 1820 are poorly covered by sunspot observations. In addition to apparent, long observational gaps, there are also periods when there are only few sparse daily sunspot observations during a ...

    I.G. Usoskin, K. Mursula, G.A. Kovaltsov in Solar Physics (2003)

  14. No Access

    Article

    Heliospheric modulation strength during the neutron monitor era

    Using a stochastic simulation of a one-dimensional heliosphere we calculate galactic cosmic ray spectra at the Earth's orbit for different values of the heliospheric modulation strength Φ. Convoluting these sp...

    I.G. Usoskin, K. Alanko, K. Mursula, G.A. Kovaltsov in Solar Physics (2002)

  15. No Access

    Article

    Simulation of Sunspot Activity During Active Sun and Great Minima Using Regular, Random and Relic Fields

    Develo** the idea of Ruzmaikin (1997, 1998), we have constructed a model of sunspot production using three components of solar magnetic field: the 22-year dynamo field, a weak constant relic field, and a ran...

    I.G. Usoskin, K. Mursula, G.A. Kovaltsov in Solar Physics (2001)

  16. No Access

    Article

    Persistent 22-year cycle in sunspot activity: Evidence for a relic solar magnetic field

    We use the recently presented group sunspot number series to show that a persistent 22-year cyclicity exists in sunspot activity throughout the entire period of about 400 years of direct sunspot observations. ...

    K. Mursula, I.G. Usoskin, G.A. Kovaltsov in Solar Physics (2001)

  17. No Access

    Article

    Adiabatic Deceleration of Solar Energetic Particles as Deduced from Monte Carlo Simulations of Interplanetary Transport

    Monte Carlo simulations of interplanetary transport are employed to study adiabatic energy losses of solar protons during propagation in the interplanetary medium. We consider four models. The first model is b...

    L. Kocharov, R. Vainio, G. A. Kovaltsov, J. Torsti in Solar Physics (1998)

  18. No Access

    Article

    Impact of Magnetic Environment on the Generation of High-Energy Neutrons at the Sun

    This paper demonstrates the important interplanetary manifestation of strongly tilted magnetic fields at the flare site. We start with analysis of Big Bear Solar Observatory (BBSO) observations of magnetic str...

    L. G. Kocharov, J. Torsti, F. Tang, H. Zirin, G. A. Kovaltsov… in Solar Physics (1997)

  19. No Access

    Article

    PHASE EVOLUTION OF SOLAR ACTIVITY AND COSMIC-RAY VARIATION CYCLES

    Cycles of phase evolution of solar activity and cosmic-ray variations are reconstructed by means of the delay component method, which allows us to study the temporal behaviour of time lag between solar activit...

    I. G. Usoskin, G. A. Kovaltsov, H. Kananen, K. Mursula, P. J. Tanskanen in Solar Physics (1997)

  20. No Access

    Article

    A joint analysis of high-energy neutrons and neutron-decay protons from a flare

    A joint analysis of neutron monitor and GOES data is performed to study the production of high-energy neutrons at the Sun. The main objects of the research are the spectrum of >50 MeV neutrons and a possible s...

    L. G. Kocharov, J. Torsti, R. Vainio, G. A. Kovaltsov, I. G. Usoskin in Solar Physics (1996)

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