List of all science nuggets

Science Nuggets

Here you can find short mini-articles, 'science nuggets', about recent discoveries made by ReSoLVE.


  • No asymptotic regime found in high-resolution stellar dynamo simulations
  • 2 June 2017

  • Three-dimensional magnetohydrodynamic simulations have recently been able to reproduce solar-like magnetic activity and non-axisymmetric large-scale magnetic fields self-consistently. The parameter regimes of such simulations are, however, still far removed from realistic conditions of stellar interiors. This study searches for an asymptotic regime where the large-scale features would no longer be dependent on the diffusion coefficients, and where the large-scale results would likely be representative of real stars. Instead, results depict that as the turbulence becomes more vigorous, differential rotation is severely quenched and no clear indication of an asymptotic regime is found even at the highest resolution. A vigorous small-scale dynamo is a possible culprit for the behavior and our results call for even higher resolution follow-up studies.

  • Reference:

    Convection-driven spherical shell dynamos at varying Prandtl numbers, Käpylä, P. J., M. J. Käpylä, N. Olspert, J. Warnecke and A. Brandenburg Astron. Astrophys., 599, A4, 2017.


  • Magnetic flux concentrations from turbulent stratified convection
  • 2 June 2017

  • The formation of magnetic flux concentrations within the solar convection zone leading to sunspot formation remains poorly known. The self-organization of initially uniform sub-equipartition magnetic fields by highly stratified turbulent convection by performing magnetoconvection simulations in local domains has been studied. Results show that super-equipartition magnetic flux concentrations are formed spontaneously from the turbulent flow. The size of the concentrations increases as the box size increases and the largest structures (20 Mm horizontally near the surface) are obtained in the models that are 24 Mm deep. The field strength in the concentrations is in the range of 3-5 kG, almost independent of the magnitude of the imposed field. The linear growth of large-scale flux concentrations implies that their dominant formation process is a tangling of the large-scale field rather than an instability. One plausible mechanism that can explain both the linear growth and the concentration of the flux in the regions of converging flow pattern is flux expulsion.

  • Reference:

    Magnetic flux concentrations from turbulent stratified convection, Käpylä,P. J., A. Brandenburg. N. Kleeorin, M. J. Käpylä and I. Rogachevskii, Astron. Astrophys., 588, A150 2016.



  • Photospheric and coronal magnetic fields in six magnetographs
    II. Harmonic scaling of field intensities
  • 1 June 2017

  • Photospheric magnetic fields have been routinely observed since the 1970s by several ground-based and satellite instruments. While the different instruments show a fairly similar large-scale structure and temporal evolution of the photospheric magnetic field, the magnetic field intensity varies significantly between the observations. A new method for scaling the photospheric magnetic field in terms of the harmonic expansion can be straightforwardly used for data sets of different resolutions.
    Different data sets generally scale to one another relatively well, with the exception of even axial terms, especially the axial quadrupole. Differences in polar field observations, pole filling, and data processing methods, as well as possible zero-level, mostly lead to a poor scaling between even axial terms. The pole-filling methods of KP and SOLIS data make the phase of the annual vantage point effect change opposite to the phase in MWO and WSO data. On the other hand, MDI pole filling appears to reduce the vantage point effect relatively successfully. The mutual scaling between SOLIS and HMI is very good, and one single overall coefficient of approximately 0.8 would be a reasonable choice for those data sets, at least up to m = 50. The slight increase of scaling factors with increasing n may relate to different spatial resolutions and related filling factors. Still, the relative errors remain rather small at least up to the studies' 180th harmonic, verifying that SOLIS and HMI synoptic maps depict similar magnetic field structures up to the resolution of 1 degree in latitude/longitude.
    Scaling factors between harmonic coefficients depend on the order of the harmonic term since the relative contribution of the different harmonic terms to the field intensity at different latitudes varies in time. Results show that comparing harmonic terms between two data sets yields a simple and accurate scaling. We note that a correct scaling for the lowest harmonics is most essential for coronal modeling, since the lowest harmonics are the most important for coronal and heliospheric magnetic fields.

  • Reference:

    Virtanen, I. I., and K. Mursula, Photospheric and coronal magnetic fields in six magnetographs: II. Harmonic scaling of field intensities Astron. Astrophys. in press 2017.


  • The worst-case scenario of solar particle storm and its terrestrial influence is assessed
  • 1 June 2017

  • Sporadic solar energetic particle (SEP) events affect the Earth's atmosphere and environment, in particular leading to depletion of the protective ozone layer in the Earth's atmosphere, and pose potential technological and even life hazards for satellites and space/air-craft crew. The strongest observed solar particle storm occurred on 23-Feb-1956 and would harm or even kill astronauts if there were some on orbit. The greatest SEP storm known from indirect proxy for the last 11 millennia (the Holocene) occurred in 774-775 AD, serving as a likely worst-case scenario. It was 40-50 times stronger than any directly observed one. A systematic analysis of the impact such an extreme event can have on the Earth’s atmosphere has been presented recently by Sukhodolov et al. (2017). Using state-of-the-art cosmic ray cascade and chemistry-climate models, they successfully reproduced the observed variability of cosmogenic isotope 10Be, around 775 AD, in four ice cores from Greenland and Antarctica, thereby validating the models in the assessment of this event. It has been shown that no nitrate deposition signal can be detected in ice cores even for such an extreme solar storm and sub-annual data resolution, thus finally proving that nitrate cannot serve as a proxy for SEP events, contrary to some earlier claims. It is shown that such a severe event is able to perturb the polar stratosphere for at least one year, leading to regional changes in the surface temperature up to several degrees centigrade during northern hemisphere winters. ReSoLVE COSMIC team (E. Asvetsari and I. Usoskin) was responsible for computations of the cosmogenic isotope production and estimate of the SEP fluxes.

  • Reference:

    Sukhodolov, T. I.G. Usoskin, E. Rozanov, E. Asvestari, W.T. Ball, M.A.J. Curran, H. Fischer, G. Kovaltsov, F. Miyake, T. Peter, C. Plummer, W. Schmutz, M. Severi, R. Traversi, Atmospheric impacts of the strongest known solar particle storm of 775 AD, Sci. Rep., 7, 45257, 2017.


  • Photospheric and coronal magnetic fields in six magnetographs
    I. Consistent evolution of the bashful ballerina
  • 17 Feb 2017

  • The hemispheric (north-south) asymmetry of solar and heliospheric magnetic fields has been studied and identified in several different parameters and by several different methods. These studies have led to the conclusion that the northern and southern solar hemispheres are connected, but not very tightly. The overall level of magnetic activity is not very different in the two hemispheres but, due to the different timing and distribution of activity, the asymmetry can be considerably large over most of the solar cycle. This study focus on the long-term evolution of photospheric and coronal magnetic fields and the heliospheric current sheet (HCS), especially its north-south asymmetry. Coronal magnetic field was constructed using synoptic maps of the photospheric magnetic field from Wilcox Solar Observatory (WSO), Mount Wilson Observatory (MWO), Kitt Peak (KP), SOLIS, SOHO/MDI and SDO/HMI, and the potential field source surface (PFSS) model. Special attention was paid to the reliability of the six data sets used, and to the consistency of the results based on them.
    The six data sets depict a fairly similar long-term evolution of magnetic fields and agree on the southward shift of the heliospheric current sheet (the so called bashful ballerina phenomenon) in the declining to minimum phase of the solar cycle. We show that during solar cycles 20 -- 22, the the southward shift of the HCS is mainly due to the axial quadrupole term, reflecting the stronger magnetic field intensity at the southern pole during these times. During cycle 23 the asymmetry is less persistent and mainly due to higher harmonics than the quadrupole term. Currently, in the early declining phase of cycle 24, the HCS is also shifted southward and is mainly due to the axial quadrupole, as for most earlier cycles. This further emphasizes the special character of the global solar field during cycle 23.

  • Reference:

    Virtanen, I.I. and K. Mursula, Photospheric and coronal magnetic fields in six magnetographs: I. Consistent evolution of the bashful ballerina Astron. Astrophys., 591, A78, 2016.


  • A new-generation model of production of cosmogenic isotopes in the Earth's atmosphere is created
  • 18 Jan 2017

  • Cosmogenic isotopes, produced by cosmic rays in the Earth's atmosphere, and stored in natural dateable archives, form the only way to reconstruct solar variability in the past. For a reliable reconstruction, one needs a precise model of their production. Several such models exist but suffer from different kinds of uncertainties. A new consistent and precise computations of the production of five cosmogenic radioisotopes, 7Be, 10Be, 14C, 22Na, and 36Cl, in the Earth’s atmosphere by cosmic rays have been performed by the team and presented in the form of tabulated yield functions, superseding previous models. For the first time, a detailed set of the altitude profiles of the production functions is provided which makes it possible to apply the results directly as input for atmospheric transport models. The new model allows now to use cosmogenic isotope data directly (Figure A), without any ad-hoc normalization, which was impossible earlier. This opens a new prospective in the studies of long-term solar variability and it possible terrestrial effects.

  • Reference:

    Poluianov, S.V., G.A. Kovaltsov, A.L. Mishev and I.G. Usoskin, Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions, J. Geophys. Res. Atmos., 121, 8125-8136, 2016.


  • The Maunder butterfly diagram extended by five cycles back, to the 1820s
  • 18 Jan 2017

  • The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, is the most important feature to study the phenomenon of solar cyclic activity. It was continuously studied since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Thanks to a collaboration with the Leibniz Institute for Astrophysics Potsdam (Germany), it has become possible to reconstruct a new extended butterfly diagram of sunspot group occurrence since 1826 (Figure A), using the recently digitized data from Schwabe (1826-1867) and Spörer (1866-1880). The presentation of the new data and their analysis has been published in two papers.

    A new method has been developed to separate the wings of the diagram, leading to a study characteristic latitudes of each wing. A new, earlier unknown strong (5-6)-cycle periodic oscillation has been found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. A marginally significant oscillation of about ten solar cycles was also found in the asymmetry of the end-cycle latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.

  • References:

    Leussu, R., I. G. Usoskin, V. Senthamizh Pavai, A. Diercke, R. Arlt, C. Denker, K. Mursula, Wings of the butterfly: Sunspot groups for 1826-2015, Astron. Astrophys., 2017.
    Leussu, R., I.G. Usoskin, R. Arlt, K. Mursula, Properties of sunspot cycles and hemispheric wings since the 19th century, Astron. Astrophys., 592, A160, 2016.



  • Sensitivity of the world neutron-monitor network for a solar neutron event is assessed
  • 27 Jun 2016

  • Free neutron are unstable with the life-time of about 10 minutes. Therefore, there is no extra-terrestrial neutrons in our environment, except of one particular case, related to strong solar flares. Sometimes protons, accelerated during a flare in a close magnetic loop in the solar atmosphere, can precipitate to the dense solar surface producing there energetic neutrons. Since neutrons are neutral, they are not trapped by the solar magnetic fields and easily escape from the Sun. Such solar neutrons can be occasionally detected at Earth, since their time of fight is comparable with the life time. It is important to detect such events since solar neutrons carry direct information of the dense layers of the solar atmosphere and surface.

    How well are we prepared to detect such events? The COSMIC team investigated this and assessed the sensitivity of the existing global network of ground-based neutron monitors (NMs), as shown in Figure A. The assessment was based on the new yield function of a standard neutron monitor 6NM64 for solar neutrons computed for a wide range of altitudes of the neutron monitor locations and angles of incidence for neutrons entering the Earth’s atmosphere. The computations were made by Monte Carlo using the GEANT4-based PLANETOCOSMICS tool. The computations were validated against the measured data for the greatest solar neutron events of 3 June 1982 and 24 May 1990, and good agreement was found.

    The neutron monitor network is shown to be a sensitive tool for monitoring of high-energy solar-flare neutrons with about 95% probability to detect statistically significantly a solar neutron event similar to that of 3 June 1982.

  • Reference:

    Artamonov, A.A., G. A. Kovaltsov, A. L. Mishev, I. G. Usoskin, Neutron monitor yield function for solar neutrons: A new computation, J. Geophys. Res., 121, 117-128, doi: 10.1002/2015JA021993, 2016.


  • A new Monte-Carlo model of atmospheric ionization by precipitating electrons is developed
  • 27 Jun 2016

  • A new model of the family of CRAC models, CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization), has been developed by the COSMIC team in the framework of the ReSoLVE task. The model calculates atmospheric ionization induced by precipitating electrons, specifically in polar regions and in middle-upper atmosphere, and uses the formalism of ionization yield functions. The CRAC:EPII model is based on a full Monte Carlo simulation of electron propagation and interaction with the air molecules. It explicitly considers various physical processes, namely, pair production, Compton scattering, generation of bremsstrahlung high-energy photons, photoionization, annihilation of positrons, and multiple scattering. It is shown that electromagnetic radiation from bremsstrahlung of electrons stopped in the upper atmosphere may contribute significantly to the ionization of the middle atmosphere, which is often neglected in simplified models, leading to incorrect results. This feature is fully taken into consideration in the new research.

    The CRAC:EPII model is applicable to the entire atmosphere. The results from the simulations are given as look-up table representing the ionization yield function. The table allows one to compute ionization due to precipitating electrons for a given altitude and location considering a given electron spectrum. Application of the model for computation of ion production during electron precipitation events using spectra from balloon-borne measurements is shown in the Figure A. Contribution form electron bremsstrahlung is visible as extended tails at larger atmospheric depths beyond 1-10 g/cm2.

  • Reference:

    Artamonov, A. A. and Mishev, A. L. and Usoskin, I. G., Model CRAC:EPII for atmospheric ionization due to precipitating electrons: Yield function and applications, J. Geophys. Res., 121, 2, 1736-1743, doi:10.1002/2015JA022276, 2016.


  • High-speed solar wind streams are the dominant driver of energetic particle precipitation
  • 13 Apr 2016

  • Disturbances of near-Earth space are predominantly driven by coronal mass ejections (CMEs) mostly originating from sunspots and high-speed solar wind streams (HSSs) emanating from coronal holes. The relative importance of CMEs and HSSs as well as slow solar wind in producing energetic electron precipitation was studied in detail in a recent paper by Asikainen and Ruopsa (2016) by utilizing the corrected energetic electron measurements from the MEPED instrument on board low-altitude NOAA/POES satellites from 1979 to 2013. Using solar wind observations categorized into three different flow types, it was possible to separate the contributions of these flows to annual electron precipitation and to quantify their efficiencies in producing precipitation. The study found that HSS contribution nearly always dominates over the other flows and peaks strongly in the declining solar cycle phase. CME contribution mostly follows the sunspot cycle but is typically enhanced also in the declining phase. Rather surprisingly the study found that the efficiency of both HSSs and also CMEs peaks in the declining phase. Detailed quantification of how the electron precipitation depends on solar wind southward magnetic field component, speed, and density revealed that the solar wind speed is the dominant factor affecting the precipitation in all solar wind flow types. It is well known that drag forces affecting the propagation of CMEs in in the interplanetary space act to either accelerate or decelerate CMEs towards background solar wind speed. Since HSSs enhance the average solar wind speed in the declining solar cycle phase, they also accelerate CMEs to higher speeds and thus enhance the efficiency of CMEs during these times. It thus seems that high-speed solar wind streams have thus have a double effect in enhancing energetic electron precipitation by also affecting the precipitation efficiency of CMEs embedded in high-speed streams.

  • Reference:

    Asikainen, T., Ruopsa, M. , Solar wind drivers of energetic electron precipitation, J. Geophys. Res., 121, doi:10.1002/2015JA022215, 2016.


  • Sunspot numbers are recalibrated and confirm the Modern grand maximum
  • 13 Apr 2016

  • Sunspot numbers provide a uniquely long index of solar activity spanning over 400 years. However they are still the subject of intense debate, with the largest uncertainty being related to the “calibration” of the visual acuity of individual observers in the past. A novel method for calibrating the visual acuity of the key solar observers in the 18th and 19th centuries to the reference data set of Royal Greenwich Observatory sunspot groups for the period 1900 – 1976, using the statistics of the active-day fraction, is presented. Observational thresholds [Ss] were defined for each observer such that the observer is assumed to miss all of the groups with an area smaller than Ss and report all the groups larger than Ss. Next, correction matrices were constructed for each observer regarding the reference data set using the Monte-Carlo method, that were applied to the original sunspot group records reported by the observers for each day (see Figure A), and finally the composite corrected series is produced for the period since 1748. The new group sunspot number series has been presented which is close to the 'classical' group sunspot number by Hoyt and Schatten (1998) but essentially lower than a recent reconstruction by Svalgaard and Schatten (2016), suggesting that the latter overestimates sunspot activity because of the used linear regression method. This result confirms the uniqueness of the grand maximum is confirmed for the last 250 years. This result is confirmed by a direct comparison with cosmogenic isotopes data of 14C in tree rings and 44Ti in fallen meteorites.

  • Reference:

    Usoskin, I.G., G.A. Kovaltsov, M. Lockwood, K. Mursula, M. Owens, S.K. Solanki, A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions, Solar Physics, 291, 2685-2708, 2016.
    Usoskin, I.G., U G.A. Kovaltsov, T. Chatzistergos, Dependence of the Sunspot-Group Size on the Level of Solar Activity and its Influence on the Calibration of Solar Observers, Solar Physics, 291, 3793-3805, 2016


  • Nitrate may serve as a new chemical proxy for long-term cosmic-ray and solar variability
  • 13 Apr 2016

  • The first direct comparison of cosmogenic 10Be record and chemical species measured in the Antarctic EPICA-Dome C ice core for the period of 38–45.5 kyr BP spanning the Laschamp geomagnetic excursion, when the geomagnetic field almost vanished, is presented. The methods of principal component analysis (PCA) and wavelet coherence (WC) were applied to group different components as a function of the main sources, transport and deposition processes affecting the atmospheric aerosol at Dome C over that period. The evident preferential association of 10Be with nitrate rather than with other chemical species was found implying for the presence of a distinct cosmogenic source of these markers. The role of calcium in driving the 10Be and nitrate relationship was shown to be insignificant, implying that the signal is mostly driven by production rather than by transport in the atmosphere. This is particularly relevant for a plateau site such as Dome C, especially in the glacial period during which the Laschamp excursion took place. The evidence that the nitrate record from the EDC ice core is able to capture the Laschamp event hints toward the possibility of using this marker for studying galactic cosmic ray flux variations and thus also major geomagnetic field excursions at pluri-centennial-millennial time scales, thus opening up new perspectives in paleoclimatic studies.

  • Reference:

    Traversi, R., S. Becagli, S. Poluianov, M. Severi, S.K. Solanki, I.G. Usoskin and R. Udisti, The Laschamp geomagnetic excursion featured in nitrate record from EPICA-Dome C ice core, Sci. Rep., 6, 20235, 2016 (doi: 10.1038/srep20235).


  • The enigmatic Hallstatt cycle (~2400 years) is of solar origin
  • 13 Apr 2016

  • The only quantitative proxy to study the long-term solar variability over a centennial-millennial timescale is related to cosmogenic isotope proxies. While essential progress has been achieved in both measurements and modelling of the cosmogenic proxy, uncertainties still remain in the determination of the geomagnetic dipole moment evolution. A new improved reconstruction of solar activity over the past nine millennia has been presented, based on cosmogenic records of 14C in tree rings and 10Be in polar ice cores, using a multi-proxy approach using the most up-to-date models of cosmogenic isotope production and transport in Earth’s atmosphere, and available geomagnetic field reconstructions, including a new reconstruction relying on an updated archeo- and paleointensity database. The reconstruction was analyzed using the singular spectrum analysis (SSA) method to study the millennial-scale trends. The primary components of the reconstructed solar activity, as determined using the SSA method, were found different for the series that are based on 14C and 10Be. This shows that these primary components can only be ascribed to long-term changes in the terrestrial system and not to the Sun. These components have therefore been removed from the reconstructed series. In contrast, the secondary SSA components of the reconstructed solar activity are found to be dominated by a common ≈2400-year quasi-periodicity, the so-called Hallstatt cycle, in both the 14C and 10Be based series. This Hallstatt cycle thus appears to be related to solar activity. It is shown that the grand minima and maxima of solar activity occurred intermittently over the studied period, with clustering near lows and highs of the Hallstatt cycle, respectively.

  • Reference:

    Usoskin, I.G., Y. Gallet, F. Lopes, G. A. Kovaltsov, G. Hulot, Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxima, Astron. Astrophys., 587, A150, 2016, doi: 10.1051/0004-6361/201527295.


  • Solar magnetic fields reconstructed from historical observations
  • 12 Nov 2015

  • Direct measurements of the solar magnetic field started in 1917 with measurements of sunspot field strength at Mount Wilson Observatory. The first magnetographic observations date back to late 1950s, with routine synoptic observations of full disk magnetograms starting in early 1970s. The full disk magnetograms provide the most complete information about polar fields, although limited information can be inferred from surface distribution of certain photospheric and chromospheric structures (e.g., polar crown filaments may outline the location of lower boundary of polar unipolar field). Correlation between bright chromospheric plages observed in Ca II K 393.37 nm spectral line and unsigned magnetic flux was noted from the very beginning of magnetographic observations in 1950s. Accordingly, the brightness of the chromospheric Ca II K spectral line available in the form of full disk images (spectroheliograms) of the Sun can be used as a proxy for solar magnetic fields.

    A recent article by Pevtsov et al. is the first in a series of articles attempting to develop a new proxy for the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements. The proxy is based on the relationship between magnetic flux and CaK line intensity (contrast) obtained from using Ca K line and sunspot magnetic field observations at Mount Wilson Observatory (MWC) and magnetograms of the National Solar Observatory at Kitt Peak. They used synoptic (Carrington) maps in 1915–1985 derived from daily Ca K line observations at Mount Wilson Observatory to identify the chromospheric plages, and to create synoptic pseudo-magnetograms. The study shows that using a combination of sunspot field measurements and the plages with renormalized intensities one can successfully construct a homogeneous long-term series of pseudo-magnetograms which highly correlate with the observed magnetic field data (correlation 0.98).

  • Reference:

    Pevtsov, A.A., I.I. Virtanen, K. Mursula, A. G. Tlatov, and L. Bertello, Reconstructing solar magnetic fields from historical observations: I. Renormalized Ca K spectroheliograms and pseudo-magnetograms, Astron. Astrophys.,in press 2015.


  • Reassessment of multiple datasets proves that the Maunder minimum (1645-1715) was indeed a grand minimum of solar activity
  • 11 Nov 2015

  • The Maunder minimum (MM) in 1645-1715 was a period when there were almost no sunspots on the Sun. This forms a paradigm for the general concept of a Grand minimum of solar activity which is important for solar/stellar dynamo theory and solar-terrestrial relations. Although the Maunder minimum was covered by the benchmark sunspot number series, uncertainties still remain on the exact level of solar activity in the 17th century. In particular, several claims were made, suggesting that it may be moderate because of the 17th century astronomers might had been affected by the dogma on the "perfectness of the Sun" which should have 'imperfect' spots.

    A reassessment of the level of solar activity during the MM was made, using all the existing, both direct and indirect, datasets and evidence has found to show that the activity was very low, significantly lower than during any other period over the last centuries including the current weak solar cycle #24. As an example, the incut Figure shows occurrence of auroral reports for 1700-1900. The green line is the number of auroral nights at geomagnetic latitudes below 56° from a combination of several catalogues. The points show the geomagnetic latitude and time of auroral sightings from the catalogue of Vázquez et al. (2014). Once can see that during the MM, auroral reports were not only significantly less frequent, but they were also high-latitude, limited to the (sub)auroral zone, indicating the absence of moderate-strong geomagnetic storms.

    The careful revision of all the presently available datasets for the Maunder minimum proves that solar activity was indeed at an exceptionally low level during that period, corresponding to a special grand minimum mode of solar dynamo.

  • Reference:

    I.G. Usoskin, R. Arlt, E. Asvestari, E. Hawkins, M. Käpylä, G.A. Kovaltsov, N. Krivova, M. Lockwood, K. Mursula, J. O’Reilly, M. Owens, C.J. Scott, D.D. Sokoloff, S.K. Solanki, W. Soon and J.M. Vaquero, The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets, A&A, 581, A95, 2015


  • Short-living cosmogenic isotope 7Be is shown to be a proxy for large scale atmospheric dynamics
  • 11 Nov 2015

  • Recent study finds that cosmogenic 7Be isotopes produced in the lower stratosphere were measured in near-ground air at Rio de Janeiro, Brazil, after the southern hemispheric Sudden Stratospheric Warming (SSW) of 2002. The study was based on a comparison of 7Be data measured around Angra Nuclear Power Station (23 S 44 W) during the last three decades and a model estimate of the near-ground air 7Be concentration using the CRAC:7Be model of cosmogenic production together with a simplified model for atmospheric 7Be deposition that assimilates the regional precipitation data. The results of the study indicate that an anomalous stratosphere-troposphere coupling associated to the unique SSW of 2002 allowed stratospheric aerosols carrying 7Be to reach the ground level very quickly. This methodology points to an important use of 7Be as a quantitative tracer for stratospheric influence on near-ground air patterns.

  • Reference:

    Pacini, A. A., I.G. Usoskin, K. Mursula, E. Echer, H. Evangelista, Signature of a sudden stratospheric warming in the near-ground 7Be flux, Atmos. Envir., 113, 27-31, 2015


  • Declining solar cycle phase favors positive NAO
  • 14 Aug 2015

  • Several recent studies have found variability in the Northern Hemisphere winter climate related to different parameters of solar activity. While these results consistently indicate some kind of solar modulation of tropospheric and stratospheric circulation and surface temperature, opinions on the exact mechanism and the solar driver differ. Proposed drivers include, e.g., total solar irradiance (TSI), solar UV radiation, galactic cosmic rays, and magnetospheric energetic particles. While some of these drivers are difficult to distinguish because of their closely similar variation over the solar cycle, other suggested drivers have clear differences in their solar cycle evolution. For example, geomagnetic activity and magnetospheric particle fluxes peak in the declining phase of the sunspot cycle, in difference to TSI and UV radiation which more closely follow sunspots. Using 13 solar cycles (1869-2009), we study winter surface temperatures and North Atlantic oscillation (NAO) during four different phases of the sunspot cycle: minimum, ascending, maximum, and declining phase. We find significant differences in the temperature patterns between the four cycle phases, which indicates a solar cycle modulation of winter surface temperatures. However, the clearest pattern of the temperature anomalies is not found during sunspot maximum or minimum, but during the declining phase, when the temperature pattern closely resembles the pattern found during positive NAO. Moreover, we find the same pattern during the low sunspot activity cycles of 100 years ago, suggesting that the pattern is largely independent of the overall level of solar activity.

  • Reference:

    Maliniemi, V., T. Asikainen, and K. Mursula, Spatial distribution of Northern Hemisphere winter temperatures during different phases of the solar cycle, J. Geophys. Res., 119, 2014.


  • New reconstruction of solar wind speed gives support to solar dynamo theory
  • 13 Aug 2015

  • In the declining phase of the solar cycle (SC), when the new-polarity fields of the solar poles are strengthened by the transport of same-signed magnetic flux from lower latitudes, the polar coronal holes expand and form non-axisymmetric extensions toward the solar equator. These extensions enhance the occurrence of high-speed solar wind (SW) streams (HSS) and related co-rotating interaction regions in the low-latitude heliosphere, and cause moderate, recurrent geomagnetic activity (GA) in the near-Earth space. Here, using a novel definition of GA at high (polar cap) latitudes and the longest record of magnetic observations at a polar cap station, we calculate the annually averaged SW speeds as proxies for the effective annual occurrence of HSS over the whole Grand Modern Maximum (GMM) from 1920s onward.

    We find that a period of high annual speeds (frequent occurrence of HSS) occurs in the declining phase of each of SCs 16-23. For most cycles the HSS activity clearly reaches a maximum in one year, suggesting that typically only one strong activation leading to a coronal hole extension is responsible for the HSS maximum. We find that the most persistent HSS activity occurred in the declining phase of SC 18. This suggests that cycle 19, which marks the sunspot maximum period of the GMM, was preceded by exceptionally strong polar fields during the previous sunspot minimum. This gives interesting support for the validity of solar dynamo theory during this dramatic period of solar magnetism.

  • Reference:

    Mursula, K., R. Lukianova, and L. Holappa, Occurrence of high-speed solar wind streams over the Grand Modern Maximum, Astrophys. J., 801, 1, 30, 2015.