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Table 1.

Hα archives analysed in this study.

Observatory Acronym Detector Instrument Period Images SW Pixel scale Ref.
[Å] [″/pixel]
Arcetri Ar Plate SHG 1931–1968 5416 0.3 2.3–4.8 (a) 1, 2
Big Bear BB CCD Filter 1988–2022 9527 0.5 4.3, 1.0 (b) 3
Boulder Bo Plate Filter 1967–1994 6864 0.5 3.7 4
Catania CT CCD Filter 2002–2022 8026 0.5 2.1, 1.3, 1.1 (c) 5
Coimbra Co Plate/CCD (d) SHG 1977–2021 8931 0.26 1.0, 2.2 (e) 6
Kanzelhöhe Ka Plate/CCD (f) Filter 1973–2022 37 276 0.7 3.0, 2.1, 2.3, 1.0 (g) 7, 8
Kharkiv Kh Plate/CCD (h) SHG 1938–2005 256 0.5 1.8, 4.0 (i) 9
Kodaikanal Ko Plate SHG 1912–2007 30 506 0.5 0.89 10
Larissa La CCD Filter 2008–2015 100 0.5 1.5, 0.8 (j) 11
McMath-Hulbert MM Plate SHG 1948–1966 3728 0.5 3.0 12
Meudon MD Plate/CCD (k) SHG 1909–2022 26 069 0.25, 0.15 (l) 0.7–4.8, 1.56, 1.1 (m) 13
Mitaka Mi Plate/CCD (n) Filter 1957–2022 34 836 0.75, 0.5, 0.25 (o) 2.8, 4.5, 2.8, 1.1 (p) 14
Pic du Midi PM CCD Filter 2011–2022 3149 0.5 1.2 15
Sacramento Peak SP Plate SHG 1960–2002 5477 0.5 1.2 16
Upice UP CCD Filter 2002–2022 1912 1.6 4, 2.5 (q) 17

Notes. Columns are the name of the observatory, abbreviation, type of detector, type of instrument, period of observations, number of images, spectral width of the spectrograph/filter, pixel scale of the image, and the bibliography entry.

(a)

Some images from 1940 and 1931 have a pixel scale of ∼4.8″ and ∼3.3″, respectively, while all other observations have a pixel scale of ∼2.5″.

(b)

The two values correspond to the periods before and after 27 November 1995.

(c)

The values correspond to the periods [23 July 2002–25 July 2006], [26 July 2006–20 September 2012], and since 21 September 2012, respectively.

(d)

The observations were stored on photographic plates up to 13 January 2007, while observations with a CCD camera started on 1 July 2008.

(e)

The two values correspond to the periods before and after 13 January 2007.

(f)

The observations were stored on photographic plates up to 10 March 2000, while observations with a CCD camera started on 24 September 1998.

(g)

The values correspond to the periods [5 May 1973–31 May 1975], [1 June 1975–10 March 2000], [24 September 1998–22 September 2010], and since 1 June 2008, respectively.

(h)

The observations since 1994 were performed with a CCD camera, while the earlier observations were stored on photographic plates.

(i)

The two values correspond to the data stored on photographic plates and those taken with a CCD camera.

(j)

The two values correspond to the periods before and after 23 September 2008.

(k)

The observations were stored on photographic plates up to 27 September 2002, while observations with a CCD camera started on 13 May 2002.

(l)

The values refer to the periods [1 January 1909–14 June 2017] and [14 June 2017–31 December 2020].

(m)

The values refer to the periods [1 January 1909–27 September 2002], [13 May 2002–14 June 2017], and [14 June 2017–31 December 2020].

(n)

The observations were stored on photographic plates up to 23 April 1992, while observations with a CCD camera started on 28 September 1991.

(o)

0.75 Å was used for the data from the Monochromatic Heliograph before 20 October 1971 and since 29 March 1974. 0.5 Å was used for the data from the Monochromatic Heliograph between 20 October 1971 and 28 March 1974 as well as those from the Automatic Flare Patrol Telescope (1991–2019, although in this work, we used the data only up to 5 May 2011). 0.25 Å was used for the Solar Flare Telescope since 6 June 2011.

(p)

The values correspond to the periods [1 October 1957–23 April 1992], [28 September 1991–28 January 2003], [25 September 2008–5 June 2011], and since 6 June 2011 respectively.

(q)

The two values correspond to the period before and after 1 January 2018, when the CCD camera was upgraded.

References. (1) Ermolli et al. (2009b); (2) Righini & Godoli (1950); (3) Denker et al. (1999); (4) Wu et al. (1975); (5) Romano et al. (2022); (6) Lourenço et al. (2019); (7) Pötzi (2008); (8) Pötzi et al. (2021); (9) Belkina et al. (1996); (10) Chatterjee et al. (2017); (11) https://www.larissa.gov.gr/dsites/larobs/SUN.htm; (12) Mohler & Dodson (1968); (13) Malherbe & Dalmasse (2019); (14) Hanaoka et al. (2020); (15) Koechlin et al. (2019); (16) Tlatov et al. (2009); (17) Klimeš et al. (1999).

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