Did the Sun Change Its Behaviour During the Decline of Cycle 23 and Into Cycle 24?

Tapping, K. F.; Valdés, Julio J.

doi:10.1007/s11207-011-9827-1

Cited by 54 publications

(54 citation statements)

References 33 publications

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“…Relative to the solar cycle 22-23 minimum, the SEM UV fluxes were 10% lower and the MgII core-to-wing ratio, a key proxy for the chromosphere and low corona, was 10% lower, an unprecedented level Solomon et al 2010Solomon et al , 2011Woods 2010b;Lean et al 2011a). Tapping & Valdés (2011) also show a drop of the minimum F 10.7 radio flux below the average of the four previous minima, but it is comparatively small (3%).…”

Section: Introductionmentioning

confidence: 67%

Are the sunspots really vanishing?

Clette

Lefèvre

2012

J. Space Weather Space Clim.

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Context:The elapsed solar cycle (23) ended with an exceptionally long period of low activity and with unprecedented low levels for various series of solar irradiance and particle flux measurements. This unpredicted evolution of solar activity raised multiple questions about a future decline of the solar cycles and launched a quest for precursor signs of this possible deep solar transition over the last decade. Aim: We present here a review and overall interpretation of most current diagnostics of solar cycle 23, including the recent disagreements that appeared among solar reference indices and standard solar-based geo-indices, the indication of a changed pattern of internal torsional waves (helioseismology) or the announced fading and magnetic weakening of sunspots. Methods: Based on a statistical analysis of detailed sunspot properties over the last 24 years, we complete the picture with new evidence of a strong global deficit of the smallest sunspots starting around 2000, in order to answer the question: are all sunspots about to disappear? Results: This global scale-dependent change in sunspot properties is confirmed to be real and not due to uncontrolled biases in some of the indices. It can also explain the recent discrepancies between solar indices by their different sensitivities to small and weak magnetic elements (small spots). The International Sunspot Index R i , based on unweighted sunspot counts, proved to be particularly sensitive to this particular small-scale solar evolution. Conclusions: Our results and interpretation show the necessity to look backwards in time, more than 80 years ago. Indeed, the Sun seems to be actually returning to a past and hardly explored activity regime ending before the 1955-1995 Grand Maximum, which probably biased our current space-age view of solar activity.

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Section: Introductionmentioning

confidence: 67%

Are the sunspots really vanishing?

Clette

Lefèvre

2012

J. Space Weather Space Clim.

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“…He concluded that the calibration of F 10.7 can be traced through the entire time series and is not drifting to higher values in the current epoch. Tapping and Valdés (2011) showed that several solar-activity indices, especially F 10.7 and R Z , are well correlated at some times and less so at others. They associated these differences with the evolution of solar activity in the different layers of the solar atmosphere.…”

Section: Changes In R Z Calibrationmentioning

confidence: 99%

“…F 10.7 The solar spectral irradiance at a wavelength of 10.7 cm [F 10.7 ] is a well-known index of solar activity, which has been measured on a daily basis since 1947 (Covington, 1969;Tapping and Charrois, 1994). F 10.7 peaks at solar maximum and fades to around 60 × 10 −22 W m −2 Hz −1 ≡ 60 SFU at solar minimum.…”

Section: R Zmentioning

confidence: 99%

Predicting Solar Cycle 24 Using a Geomagnetic Precursor Pair

Pesnell

2014

Sol Phys

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We describe using Ap and F 10.7 as a geomagnetic-precursor pair to predict the amplitude of Solar Cycle 24. The precursor is created by using F 10.7 to remove the direct solar-activity component of Ap. Four peaks are seen in the precursor function during the decline of Solar Cycle 23. A recurrence index that is generated by a local correlation of Ap is then used to determine which peak is the correct precursor. The earliest peak is the most prominent but coincides with high levels of non-recurrent solar activity associated with the intense solar activity of October and November 2003. The second and third peaks coincide with some recurrent activity on the Sun and show that a weak cycle precursor closely following a period of strong solar activity may be difficult to resolve. A fourth peak, which appears in early 2008 and has recurrent activity similar to precursors of earlier solar cycles, appears to be the "true" precursor peak for Solar Cycle 24 and predicts the smallest amplitude for Solar Cycle 24. To determine the timing of peak activity it is noted that the average time between the precursor peak and the following maximum is ≈ 6.4 years. Hence, Solar Cycle 24 would peak during 2014. Several effects contribute to the smaller prediction when compared with other geomagnetic-precursor predictions. During Solar Cycle 23 the correlation between sunspot number and F 10.7 shows that F 10.7 is higher than the equivalent sunspot number over most of the cycle, implying that the sunspot number underestimates the solar-activity component described by F 10.7 . During 2003 the correlation between aa and Ap shows that aa is 10 % higher than the value predicted from Ap, leading to an overestimate of the aa precursor for that year. However, the most important difference is the lack of recurrent activity in the first three peaks and the presence of significant recurrent activity in the fourth. While the prediction is for an amplitude of Solar Cycle 24 of 65 ± 20 in smoothed sunspot number, a below-average amplitude for Solar Cycle 24, with maximum at 2014.5 ± 0.5, we conclude that Solar Cycle 24 will be no stronger than average and could be much weaker than average.

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“…Several recent studies have shown that F 10.7 and SN were in fair agreement until 1995 but then started to diverge, with the SN falling significantly below F 10.7 after 2000 (Svalgaard and Hudson, 2010;Lukianova and Mursula, 2011;Tapping and Valdés, 2011;Clette and Lefèvre, 2012). Clette et al (2014) already showed that by applying the correction for the Locarno drifts, which precisely cause an underestimate of the SN after 2000, the difference between the two series was cut by about half, but that a significant disagreement was still present for that interval.…”

Section: Inhomogeneities In F 107mentioning

confidence: 99%

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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Did the Sun Change Its Behaviour During the Decline of Cycle 23 and Into Cycle 24?

Cited by 54 publications

References 33 publications

Are the sunspots really vanishing?

Are the sunspots really vanishing?

Predicting Solar Cycle 24 Using a Geomagnetic Precursor Pair

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

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