Reconstruction of Solar Extreme Ultraviolet Flux 1740 – 2015

Svalgaard, Leif

doi:10.1007/s11207-016-0921-2

Cited by 23 publications

(26 citation statements)

References 58 publications

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“…They discussed how the ionospheric conductivity is proportional to the square root of the solar EUV flux, not to the EUV flux itself. Good agreement between the Sq amplitude and solar activity parameters presented in Table 4 suggests that those solar indices can be estimated or calibrated using Sq data (Svalgaard andCliver 2007, Svalgaard 2016). However, such an application requires some caution; for example, as seen in Table 4, the average over longitude seems to be important for accurately estimating solar activity from rY .…”

Section: Sq Current Intensitymentioning

confidence: 89%

“…Geomagnetic disturbances associated with storms and substorms are typically several hundreds of nano teslas on the surface, which can easily mask underlying Sq signals. Despite the small amplitude, studies on Sq have been important for understanding the ionospheric electrodynamics (Richmond 1979(Richmond , 1995b and its coupling to the magnetosphere and lower atmosphere (Wagner et al 1980;Richmond 1995b); for determining a base level for geomagnetic indices (Mayaud 1980;Love and Gannon 2009;Gjerloev 2012); for monitoring solar radiation activity (Svalgaard and Cliver 2007;Svalgaard 2016); and for estimating electrical conductivity within the Earth (Campbell and Schiffmacher 1988a;Campbell et al 1998;Okeke and Obiora 2016).…”

Section: Observational Overviewmentioning

confidence: 99%

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Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

2016

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A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several μA/m 2 flowing on the sunlit side of the Eregion ionosphere at about 90-150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the nonspecialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

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Section: Sq Current Intensitymentioning

confidence: 89%

Section: Observational Overviewmentioning

confidence: 99%

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

2016

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“…Assessment can be performed only using indirect proxies, such as geomagnetic, heliospheric or cosmogenic. Several such efforts have been made but turned inconclusive and mutually controversial (Lockwood et al 2016a,c;Owens et al 2016a;Svalgaard 2016). Moreover, Svalgaard (2016), using data on the diurnal variability of the geomagnetic field, proposed that 'the Relative Sunspot Number as currently defined is beginning to no longer be a faithful representation of solar magnetic activity', implying a discrepancy between geomagnetic and sunspot records.…”

Section: Introductionmentioning

confidence: 99%

“…Several such efforts have been made but turned inconclusive and mutually controversial (Lockwood et al 2016a,c;Owens et al 2016a;Svalgaard 2016). Moreover, Svalgaard (2016), using data on the diurnal variability of the geomagnetic field, proposed that 'the Relative Sunspot Number as currently defined is beginning to no longer be a faithful representation of solar magnetic activity', implying a discrepancy between geomagnetic and sunspot records. Cosmogenic isotopes, mostly 14 C and 10 Be, measured in natural terrestrial archives, provide a quantitative proxy for solar activity (Beer, McCracken & von Steiger 2012;Usoskin 2013).…”

Section: Introductionmentioning

confidence: 99%

Assessment of different sunspot number series using the cosmogenic isotope ⁴⁴ Ti in meteorites

Asvestari

Usoskin

Kovaltsov

et al. 2017

Mon. Not. R. Astron. Soc.

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Many sunspot number series exist suggesting different levels of solar activity during the past centuries. Their reliability can be assessed only by comparing them with alternative indirect proxies. We test different sunspot number series against the updated record of cosmogenic radionuclide 44 Ti measured in meteorites. Two bounding scenarios of solar activity changes have been considered: the HH-scenario (based on the series by Svalgaard and Schatten), in particular, predicting moderate activity during the Maunder minimum, and the LL-scenario (based on the R G series by Lockwood et al.) predicting moderate activity for the 18th-19th centuries and the very low activity level for the Maunder minimum. For each scenario, the magnetic open solar flux, the heliospheric modulation potential and the expected production of 44 Ti were computed. The calculated production rates were compared with the corresponding measurements of 44 Ti activity in stony meteorites fallen since 1766. The analysis reveals that the LL-scenario is fully consistent with the measured 44 Ti data, in particular, recovering the observed secular trend between the 17th century and the Modern grand maximum. On the contrary, the HH-scenario appears significantly inconsistent with the data, mostly due to the moderate level of activity during the Maunder minimum. It is concluded that the HHscenario sunspot number reconstruction significantly overestimates solar activity prior to the mid-18th century, especially during the Maunder minimum. The exact level of solar activity after 1750 cannot be distinguished with this method, since both H-and L-scenarios appear statistically consistent with the data.

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“…Given the different information contained in those two numbers, this may reflect actual changes in solar properties over years and centuries. For instance, several studies show a decline in the SN/GN ratio since cycle 19, which seems to amplify after the maximum of cycle 23 around 2000 (Svalgaard and Hudson, 2010;Clette and Lefèvre, 2012;Svalgaard, 2015). This suggests a corresponding decline in the average number of spots per groups.…”

Section: Group Number Versus Sunspot Number: a Constant Non-linear Rementioning

confidence: 98%

The Revised Brussels–Locarno Sunspot Number (1981 – 2015)

et al. 2016

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In 1981, the production of the international Sunspot Number moved from the Zürich Observatory to the Royal Observatory of Belgium, with a new pilot station, the Specola Solare Ticinese Observatory in Locarno. This marked a very important transition in the history of the Sunspot Number. Those recent decades are particularly important as they provide the link between recent modern solar indices and fluxes and the entire Sunspot Number series extending back to the 18 th century. However, large variations have been recently identified in the scale of the Sunspot Number between 1981 and the present. Here, we refine the determination of those recent inhomogeneities by reconstructing a new average Sunspot Number series S N from a subset of long-duration stations between 1981 and 2015. We also extend this reconstruction by gathering long-time series from 35 stations over 1945-2015, thus straddling the critical 1981 transition. In both reconstructions, we also derive a parallel Group Number series G N built by the same method from exactly the same data set. Our results confirm the variable trends associated with drifts of the Locarno pilot station, which start only in 1983. We also verify the scale of the resulting 1981-2015 correction factor relative to the preceding period , which leads to a fully uniform S N series over the entire 1945-2015 interval. By comparing the new S N and G N series, we find that a constant quadratic relation exists between those two indices. This proxy relation leads to a fully constant and cycle-independent S N /G N ratio over cycles 19 to 23, with the exception of cycle 24 where it drops to a lower value. Several comparisons with other indices show a very good agreement between our reconstructed G N and the new "backbone" Group Number (Clette et al., 2014) but reveal inhomogeneities in the original Group Number as well as the F 10.7 radio flux and the American sunspot number R a over the period 1945-2015.

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Reconstruction of Solar Extreme Ultraviolet Flux 1740 – 2015

Cited by 23 publications

References 58 publications

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Assessment of different sunspot number series using the cosmogenic isotope ⁴⁴ Ti in meteorites

The Revised Brussels–Locarno Sunspot Number (1981 – 2015)

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Reconstruction of Solar Extreme Ultraviolet Flux 1740 – 2015

Cited by 23 publications

References 58 publications

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Assessment of different sunspot number series using the cosmogenic isotope 44 Ti in meteorites

The Revised Brussels–Locarno Sunspot Number (1981 – 2015)

Contact Info

Product

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Assessment of different sunspot number series using the cosmogenic isotope ⁴⁴ Ti in meteorites