Jan Olof Stenflo


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Stenflo

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Jan Olof

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0000-0002-5524-6628

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2005 - 200912020 - 20254
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Publications 1 - 5 of 5
  • So Far, so Good - My First 82 Years
    Item type: Journal Article
    Stenflo, Jan Olof (2025)
    Solar Physics
    My romantic attraction to the stars started at the age of 11 under the dark Swedish skies. While it was clear from then on that I wanted to be an astronomer, a sequence of chance encounters led me to choose solar physics and embark on an unpredictable path across the globe, including work for my PhD in the USSR about the Sun's magnetic field, followed by an experiment on a Soviet satellite to record scattering polarization on the Sun. On my first hike in the Rocky Mountains in 1971, I had a chance encounter with my future wife and married 4 months later in Sweden. In 1980, we moved to Switzerland for 43 years. Finally, our geographically scattered family reunited. All of us, sons and grandsons, are now settled in Colorado. My story tells how this unplanned path was intertwined with the search for answers about the nature of solar magnetism.
  • Evolution and rotation of large-scale photospheric magnetic fields of the Sun during cycles 21-23
    Item type: Review Article
    Knaack, Reto; Stenflo, Jan Olof; Berdyugina, Svetlana V. (2005)
    Astronomy & Astrophysics
    We present the results of an extensive time series analysis of longitudinally-averaged synoptic maps, recorded at the National Solar Observatory (NSO/Kitt Peak) from 1975 to 2003, and provide evidence for a multitude of quasi-periodic oscillations in the photospheric magnetic field of the Sun. In the low frequency range, we have located the sources of the 3.6 yr, 1.8 yr, and 1.5 yr periodicities that were previously detected in the north- south asymmetry of the unsigned photospheric flux (Knaack et al. 2004, A&A, 418, L17). In addition, quasi-periodicities around 2.6 yr and 1.3 yr have been found. The 1.3 yr period is most likely related to large-scale magnetic surges toward the poles and appeared in both hemispheres at intermediate latitudes ∼30°-55° during the maxima of all three cycles 21-23, being particularly pronounced during cycle 22. Periods near 1.3 yr have recently been reported in the rotation rate at the base of the convection zone (Howe et al. 2000, Science, 287, 2456), in the interplanetary magnetic field and geomagnetic activity (Lockwood 2001, J. Geophys. Res., 106, 16021) and in sunspot data (Krivova & Solanki 2002, A&A, 394, 701). In the intermediate frequency range, we have found a series of quasiperiodicities of 349-307 d, 282 ± 4 d, 249-232 d, 222-209 d, 177 ±2 d, 158-151 d, 129-124 d and 103-100 d, which are in good agreement with period estimates for Rossby-type waves and occurred predominantly in the southern hemisphere. We provide evidence that the best known of these periodicities, the Rieger period around 155 d, appeared in the magnetic flux not only during cycle 21 but also during cycle 22, likely even during cycle 23. The high frequency range, which covers the solar rotation periods, shows a dominant (synodic) 28.1 ± 0.1 d periodicity in the southern hemisphere during cycles 21 and 22. A periodicity around 25.0-25.5 d occurred in the south during all three cycles. The large-scale magnetic field of the northern hemisphere showed dominant rotation periods at 26.9 ± 0. 1 d during cycle 21, at 28.3-29.0 d during cycle 22 and at 26.4 ±0.1 d during cycle 23.
  • The European Solar Telescope
    Item type: Journal Article
    Quintero Noda, Carlos; Schlichenmaier, Rolf; Bellot Rubio, Luis Ramon; et al. (2022)
    Astronomy & Astrophysics
    The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Telescope Heliographique pour l'etude du Magnetisme et des Instabilites Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems.
  • Use of Redshifts as Evidence of Dark Energy
    Item type: Journal Article
    Stenflo, Jan Olof (2025)
    Physics
    The large-scale dynamics of the universe is generally described in terms of the time-dependent scale factor a(t). To make contact with observational data, the a(t) function needs to be related to the observable z(r) function, redshift versus distance. Model fitting of data has shown that the equation that governs z(r) needs to contain a constant term, which has been identified as Einstein’s cosmological constant. Here, it is shown that the required constant term is not a cosmological constant but is due to an overlooked geometric difference between proper time t and look-back time tlb along lines of sight, which fan out isotropically in all directions of the 3D (3-dimensional) space that constitutes the observable universe. The constant term is needed to satisfy the requirement of spatial isotropy in the local limit. Its magnitude is independent of the epoch in which the observer lives and agrees with the value found by model fitting of observational data. Two of the observational consequences of this explanation are examined: an increase in the age of the universe from 13.8 Gyr to 15.4 Gyr, and a resolution of the H0 tension, which restores consistency to cosmological theory.
  • Cosmological Constant from Boundary Condition and Its Implications beyond the Standard Model
    Item type: Journal Article
    Stenflo, Jan Olof (2023)
    Universe
    Standard cosmology has long been plagued by a number of persistent problems. The origin of the apparent acceleration of the cosmic expansion remains enigmatic. The cosmological constant has been reintroduced as a free parameter with a value in energy density units that “happens” to be of the same order as the present matter energy density. There is an internal inconsistency with regards to the Hubble constant, the so-called (Formula presented.) tension. The derived value of (Formula presented.) depends on the type of data that is used. With supernovae as standard candles, one gets a (Formula presented.) that is 4–5 (Formula presented.) larger than the value that one gets from CMB (Cosmic Microwave Background) data for the early universe. Here we show that these problems are related and can be solved if the cosmological constant represents a covariant integration constant that arises from a spatial boundary condition, instead of being a new type of hypothetical physical field, “dark energy”, as assumed by standard cosmology. The boundary condition only applies to the bounded 3D subspace that represents the observable universe, the hypersurface of the past light cone.
Publications 1 - 5 of 5