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Hhudson — Thu, 14 May 2026 10:50:24 GMT

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	Welcome to the [[SolarNuggets]] collection, which extends the series of [[RHESSI]] Nuggets. The following is a time-ordered list of the latest Nuggets added to the HelioWiki. An [[:Category:Nugget\|alphabetical list of the SolarNuggets]] is also available as well as [[:Category:RHESSI Nugget List\|yearly lists]]. One can search on author, topic, IAU flare identifier, etc.). We welcome volunteer authors - please see our page of [[Help:For_Authors\| help for authors]] or just send an email to the Curator at (hugh.hudson@glasgow.ac.uk).		Welcome to the [[SolarNuggets]] collection, which extends the series of [[RHESSI]] Nuggets. The following is a time-ordered list of the latest Nuggets added to the HelioWiki. An [[:Category:Nugget\|alphabetical list of the SolarNuggets]] is also available as well as [[:Category:RHESSI Nugget List\|yearly lists]]. One can search on author, topic, IAU flare identifier, etc.). We welcome volunteer authors - please see our page of [[Help:For_Authors\| help for authors]] or just send an email to the Curator at (hugh.hudson@glasgow.ac.uk).

			{{Nugget Badge
			\|title = X-ray Log Letters‎‎
			\|number = 526
			\|first_author = Hugh HUDSON
			\|second_author = and Ed CLIVER
			\|\|publish_date = 18 May 2026
			\|description = Replacing ABCMX with a new comprehensive and quantitative QSabcmxyz catalog
			\|image=Icon526.png}}


	{{Nugget Badge		{{Nugget Badge

File:Icon526.png

Hhudson — Thu, 14 May 2026 10:46:04 GMT

Hhudson uploaded File:Icon526.png

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X-ray Log Letters

Hhudson — Thu, 14 May 2026 10:42:04 GMT

Conclusions

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	Flares of a wide range of brightnesses were immediately apparent, and		Flares of a wide range of brightnesses were immediately apparent, and
	[https://www.noaa.gov NOAA]		[https://www.noaa.gov NOAA]
	ionospheric physicist Don Baker (Ref. [1]) came up with the ~~classification~~.		ionospheric physicist Don Baker (Ref. [1]) came up with a classification
			that matched decades of peak flux to letters: Cnn would mean nn x 10<sup>-4</sup>,
			and the basic flux level 1.0 x 10<sup>-6</sup> W/m<sup>2</sup> would be class C1.0.
	Initially it was just CMX ("Common", "Medium", "Extreme")		Initially it was just CMX ("Common", "Medium", "Extreme")
	Each flare has a peak flux in the standard 1-8 Å band,		Each flare has a peak flux in the standard 1-8 Å band,
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	Low background solar X-ray fluxes during solar minima allowed the GOES		Low background solar X-ray fluxes during solar minima allowed the GOES
	detector technology to detect fainter events, and so two new decades were		detector technology to detect fainter events, and so two new decades were
	added to the letter string: A and B, with no descriptive ~~term ("Boring" and~~		added to the letter string: A and B, with no particular descriptive
	~~"Anemic" come to mind)~~.		interpretation.
	Thus we ~~have~~ ABCMX.		Thus we arrived at the current letter string ABCMX.

	== The SphinX breakthrough (to the bottom) ==		== The SphinX breakthrough (to the bottom) ==
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	below the original CMX range (Ref. [3]).		below the original CMX range (Ref. [3]).
	Excesses above this level are due to weak flares and quiescent active regions.		Excesses above this level are due to weak flares and quiescent active regions.
			Translated to the GOES calibration, the weakest events are measured in units of
			10<sup>-10</sup> W/m<sup>2</sup>.
	</i>]]		</i>]]

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	At the top end of the GOES soft X-ray distribution, a handful of the most		At the top end of the GOES soft X-ray distribution, a handful of the most
	extreme events had saturated the 1-8 Å readout.		extreme events had saturated the GOES 1-8 Å readout.
	Ref. [4] describes an evenhanded patching of these items, together with a		Ref. [4] describes an evenhanded patching of these items, together with a
	~~correcting~~ for a systematic offset (Ref. [2]).		correction for a systematic offset (Ref. [2]).
	This produced a list of 37 >X10 events after background subtraction.		This produced a list of 37 >X10 events after background subtraction.
	This basic manipulation departs from tradition, and so we provide this		This basic manipulation departs from tradition, and so we provide this
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	[https://heliowiki.smce.nasa.gov/wiki/index.php/The_1859_Space_Weather_Event_Revisited Carrington event]		[https://heliowiki.smce.nasa.gov/wiki/index.php/The_1859_Space_Weather_Event_Revisited Carrington event]
	might have been in that category.		might have been in that category.

			A sample of the newly lettered catalog is here, representing a signal-to-background requirement of 1 (flare
			doubles the preflare level), resulting in a reduction of total number from 48,131 to 42,469 for the timespan
			1974-2023.
			The new letter string is QSabcmxyz, pleasingly symmetric.
			SOL1984-02-10T22:47 C9.1 m1.21
			SOL1984-02-11T01:31 C3.7 c3.78
			SOL1984-02-11T02:45 M2.9 m4.07
			SOL1984-02-11T03:44 C2.0 c1.93
			SOL1984-02-11T04:33 C2.1 c1.78
			SOL1984-02-11T04:56 C2.1 c2.23
			SOL1984-02-11T09:06 C2.6 c2.46
			SOL1984-02-11T10:09 C1.8 c1.43
			SOL1984-02-11T12:16 C3.0 c3.19
			SOL1984-02-11T14:24 C4.8 c6.03
			The catalog contains 37 y-class events (previously X10 or S), but no z-class examples because the Sun refuses to
			cooperate. At the C->c level, many events get downgraded because of background subtraction, but the systematic
			historical scale adjustment described in Ref. [2] tends to compensate for that.

	== Conclusions ==		== Conclusions ==

			See the [https://www.astro.gla.ac.uk/users/hsh3f/QSabcmxyz.html further discussion] of how QSabcmxyz works, or to access it directly click [https://www.astro.gla.ac.uk/users/hsh3f/QSabcmxyz.txt here] for a 2-MB text listing.

	== References ==		== References ==

X-ray Log Letters

Hhudson — Mon, 11 May 2026 18:31:11 GMT

Most of No. 526

New page

{{Infobox Nugget |name = Nugget
|title = X-ray Log Letters
|number = 526
|first_author = Hugh HUDSON and
|second_author = Ed CLIVER
|publish_date = May 18, 2026
|next_nugget = TBD
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::525]]}}
}}

== Introduction ==

As all students of solar activity know, the
[https://www.stce.be/educational/classification naming scheme]
for solar flares involves the letters ABCMX.
These date from the dawn of the space age, when the first
[https://en.wikipedia.org/wiki/SOLRAD SOLRAD] satellites began to monitor
solar X-ray emission.
Flares of a wide range of brightnesses were immediately apparent, and
[https://www.noaa.gov NOAA]
ionospheric physicist Don Baker (Ref. [1]) came up with the classification.
Initially it was just CMX ("Common", "Medium", "Extreme")
Each flare has a peak flux in the standard 1-8 Å band,
and the range of magnitudes of flare peak fluxes is so great that it's most
convenient to record the
[https://en.wikipedia.org/wiki/Common_logarithm logarithm] of the
flux.
This convention moved directly into the
[https://www.swpc.noaa.gov/products/goes-x-ray-flux GOES]
satellite era, and from 1974 the standardized flux measurements
have come from this series of spacecraft (Ref. [2]).

In standard units a C-class flare has a peak flux greater than 10-7
W/m2, with M-class and X-class greater by powers of 10.
Conventionally a flare 10% brighter than the threshold, with peak flux
1.1 x 10-7 W/m2, would then become a C1.1 flare.
The letter thus represents the truncated logarithm of the peak flux.
The magnitudes are not rounded off and represent the solar X-ray flux
conventionally in a 1-min integration interval.
A background quiescent solar emission level is not subtracted; these routine
observations show the total solar X-ray flux in "Sun-as-a-star" mode.
Weaker events near the background level, which can indeed exceed C1 during
active times, will thus not be quite as energetic as their name implies.

Low background solar X-ray fluxes during solar minima allowed the GOES
detector technology to detect fainter events, and so two new decades were
added to the letter string: A and B, with no descriptive term ("Boring" and
"Anemic" come to mind).
Thus we have ABCMX.

== The SphinX breakthrough (to the bottom) ==

The first routine flare monitoring with sufficient sensitivity to
detect the solar quiescent X-ray flux appeared with the SphinX
instrument from the
[https://scholar.google.com/citations?user=vDLMZPIAAAAJ&hl=pl Sylwester]
group at Wroc&lstrok;aw (Ref. [3]).
For 1-8 Å this turned out to be about two decades below the A level.
Hence, two more letters: Q "quiet" and S "small", leading to the more complete
string QSABCMX.
Figure 1 shows SphinX data from the 2009
[https://en.wikipedia.org/wiki/Solar_cycle solar minimum].

[[File:526f1.png|center|thumb|600px|caption|Figure 1: 
SphinX observations from solar minimum 2009.
The regions marked with blue show the detection of the corona, at levels far
below the original CMX range (Ref. [3]).
Excesses above this level are due to weak flares and quiescent active regions.
]]

== The greatest events (to the top) ==

At the top end of the GOES soft X-ray distribution, a handful of the most
extreme events had saturated the 1-8 Å readout.
Ref. [4] describes an evenhanded patching of these items, together with a
correcting for a systematic offset (Ref. [2]).
This produced a list of 37 >X10 events after background subtraction.
This basic manipulation departs from tradition, and so we provide this
[greatest flares]
catalog using the letter system "QSabcmxyz".
To translate, the new "y" class is the old "X10" class, sometimes now called
"S" (Ref. 5]), and the new catalog lists 37 of them.
The new "z" class has no examples yet (but we're hopeful), although the
[https://heliowiki.smce.nasa.gov/wiki/index.php/The_1859_Space_Weather_Event_Revisited Carrington event]
might have been in that category.

== Conclusions ==

== References ==

[1] "Sentinels of the sun: forecasting space weather," B. Poppe and K. Jorden, 2006

[2] [https://www.sciencedirect.com/science/article/pii/B9780128143278000196 "GOES-R Series Solar X-ray and Ultraviolet Irradiance"]

[3] [http://adsabs.harvard.edu/abs/2011SoSyR..45..182G "Soft X-ray variability over the present minimum of solar activity as observed by SphinX"]

[4] [https://ui.adsabs.harvard.edu/abs/2024SoPh..299...39H "The Greatest GOES Soft X-ray Flares"]

[5] [https://ui.adsabs.harvard.edu/abs/2025ApJ...979L..16T "The Occurrence of Powerful Flares Stronger than X10 Class in Solar Cycles"]

File:526f1.png

Hhudson — Mon, 11 May 2026 18:17:13 GMT

Hhudson uploaded File:526f1.png

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