Bastille Day 2017

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|second_author = Säm Krucker
|second_author = Säm Krucker
|publish_date = 24 July 2017
|publish_date = 24 July 2017
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|next_nugget = The thrill of solar minimum
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|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::304]]}}
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|previous_nugget = [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Solar_X-ray_Limb_III Solar X-ray Limb]
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|previous_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::302]]}}
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For unclear reasons,  
For unclear reasons,  
[https://en.wikipedia.org/wiki/Bastille_Day July 14] has seen several interesting flares, such
[https://en.wikipedia.org/wiki/Bastille_Day July 14] has seen several interesting flares, such
-
as the famous one termed the "Bastille Day Flare" in 2000.
+
as the famous one originally termed ''the'' "Bastille Day Flare" in 2000.
This flare (SOL2000-07-14, M5.7) has been well memorialized in the literature
This flare (SOL2000-07-14, M5.7) has been well memorialized in the literature
-
and in various Nuggets, but back in the  
+
and in various Nuggets, but the latter were back in the  
[https://en.wikipedia.org/wiki/Yohkoh ''Yohkoh''] era  
[https://en.wikipedia.org/wiki/Yohkoh ''Yohkoh''] era  
([http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000714/000714.html i],
([http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000714/000714.html i],
[http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000825/000825.html ii],
[http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000825/000825.html ii],
-
[http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000915/000915.html iii].
+
[http://ylstone.physics.montana.edu/ystorage/nuggets/2000/000915/000915.html iii]).
Many lessons were learned from this flare, which had a fine display of loops
Many lessons were learned from this flare, which had a fine display of loops
that remains an iconic illustration of this  
that remains an iconic illustration of this  
-
[https://apod.nasa.gov/apod/ap000720.html flare arcade] structural development.
+
[https://apod.nasa.gov/apod/ap000720.html flare arcade] coronal restructuring.
Reference [1] introduced the world to this event as an epitome of the effects
Reference [1] introduced the world to this event as an epitome of the effects
of large-scale flare
of large-scale flare
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Then in 2004 another Bastille Day event happened, SOL2004-07-14 (M6.2),
Then in 2004 another Bastille Day event happened, SOL2004-07-14 (M6.2),
-
which now lay in the RHESSI era but somehow did not produce a Nugget (see however
+
which now fell in the RHESSI era (and was well observed in hard X-rays)
 +
but somehow did not produce a Nugget (see however
Ref. [2]); a description of magnetic implosion in a confined flare event..
Ref. [2]); a description of magnetic implosion in a confined flare event..
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SOL2017-07-14 (M2.4) occur in the declining phase of
SOL2017-07-14 (M2.4) occur in the declining phase of
[https://en.wikipedia.org/wiki/Solar_cycle Solar Cycle] 24.
[https://en.wikipedia.org/wiki/Solar_cycle Solar Cycle] 24.
-
This event, illustrated in Figure 2, dominates the soft X-ray landscape with the  
+
This event, illustrated in Figure 2, dominates the soft X-ray timescape with the  
long-decay property suggestive of an extended coronal event, with a
long-decay property suggestive of an extended coronal event, with a
[https://en.wikipedia.org/wiki/Coronal_mass_ejection CME] and radio  
[https://en.wikipedia.org/wiki/Coronal_mass_ejection CME] and radio  
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This appears to have been the case, although some of the needed data are not  
This appears to have been the case, although some of the needed data are not  
available quite yet.
available quite yet.
-
As the right panel of Figure 2 shows, this event had the sigmoid-to-arcade
 
-
development typical of this kind of flare (Ref. [3]).
 
-
Note that RHESSI's hard X-ray footpoints neatly fit into the flare ribbon
 
-
structures - just like SOL2000-07-14 where the concept of a "Bastille Day Flare"
 
-
originated.
 
-
[[File:303f4.png|600px|thumb|center|Figure 2: Left, three days of
+
[[File:303f3.png|400px|thumb|center|Figure 2: Three days of
[https://www.solarmonitor.org/index.php?date=20170715&region=&indexnum=1 GOES/XRS]  
[https://www.solarmonitor.org/index.php?date=20170715&region=&indexnum=1 GOES/XRS]  
soft X-ray observation,
soft X-ray observation,
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Right, RHESSI hard-ray image contours superposed on a
Right, RHESSI hard-ray image contours superposed on a
background EUV image from [http://aia.lmsal.com AIA].  
background EUV image from [http://aia.lmsal.com AIA].  
 +
]]
 +
 +
RHESSI observed this event quite well.
 +
Figure 3 shows that this event had the sigmoid-to-arcade
 +
development typical of this kind of flare (Ref. [3]).
 +
Note that RHESSI's hard X-ray footpoints neatly fit into the flare ribbon
 +
structures - just like SOL2000-07-14 where the concept of a "Bastille Day Flare"
 +
originated.
 +
The spectrum at flare maximum (right panel) shows soft and hard X-ray components consistent
 +
with our observations of similar events.
 +
 +
[[File:303f4.png|700px|thumb|center|Figure 3:
 +
Left, RHESSI hard-ray image contours superposed on a
 +
background EUV image from [http://aia.lmsal.com AIA].
 +
Right, spectrum from flare peak (courtesy B. Dennis).
]]
]]
=== Conclusions ===
=== Conclusions ===
-
Is Bastille Day, over the decades, really a focus for major solar activity?
+
Is Bastille Day, over the decades, really a focus for major solar fireworks?
This would be highly unlikely, and although we have cited four major events  
This would be highly unlikely, and although we have cited four major events  
in 18 years here, that is not far from what one expect from a  
in 18 years here, that is not far from what one expect from a  
-
reasonable mean level of solar activity.
+
reasonable mean level of solar activity - about a 25% chance, per day, of seeing an M- or X-class flare.
-
A crude prediction for 2018 then would say that, factoring in a guess at
+
For RHESSI's first 11-year time span, the corresponding rate was 0.23 +- 0.03.
-
the solar-cycle dependence, there is only about a 1% chance of another  
+
So, no exceptionalism here.
-
remarkable event then - stay tuned to these pages and we will let you know then.
+
 
 +
A crude prediction for 2018 then, factoring in a guess at
 +
the solar-cycle dependence, suggests only about a 10% chance of another  
 +
remarkable event next year - stay tuned to these pages and we will let you know then.
=== References ===
=== References ===

Latest revision as of 18:57, 22 August 2018


Nugget
Number: 303
1st Author: Hugh Hudson
2nd Author: Säm Krucker
Published: 24 July 2017
Next Nugget: RHESSI and the Megamovie
Previous Nugget: The Solar X-ray Limb III
List all



Contents

Introduction

For unclear reasons, July 14 has seen several interesting flares, such as the famous one originally termed the "Bastille Day Flare" in 2000. This flare (SOL2000-07-14, M5.7) has been well memorialized in the literature and in various Nuggets, but the latter were back in the Yohkoh era (i, ii, iii). Many lessons were learned from this flare, which had a fine display of loops that remains an iconic illustration of this flare arcade coronal restructuring. Reference [1] introduced the world to this event as an epitome of the effects of large-scale flare magnetic reconnection.

Figure 1: The celebrated soft X-ray/EUV "arcade" structure of the original Bastille Day flare, SOL2000-07-14, as obtained from the Astronomical Picture of the Day website. It shows a 171 Â image from the TRACE satellite.

Then in 2004 another Bastille Day event happened, SOL2004-07-14 (M6.2), which now fell in the RHESSI era (and was well observed in hard X-rays) but somehow did not produce a Nugget (see however Ref. [2]); a description of magnetic implosion in a confined flare event..

The very next year Bastille Day saw an X-class flare, SOL2005-07-14 (X1.2), which did excite a RHESSI-era Nugget (iv). This flare was curious in that it had no well-developed CME and instead revealed a "failed" filament eruption, but also exhibited an implosion.

Bastille Day 2017

So far as we can tell, no other memorable flare has happened on Bastille Day since 2005. But here, one 11-year cycle later, we have had SOL2017-07-14 (M2.4) occur in the declining phase of Solar Cycle 24. This event, illustrated in Figure 2, dominates the soft X-ray timescape with the long-decay property suggestive of an extended coronal event, with a CME and radio type II/IV emissions. This appears to have been the case, although some of the needed data are not available quite yet.

Figure 2: Three days of GOES/XRS soft X-ray observation, indicating the dominance of our Bastille Day flare. Right, RHESSI hard-ray image contours superposed on a background EUV image from AIA.

RHESSI observed this event quite well. Figure 3 shows that this event had the sigmoid-to-arcade development typical of this kind of flare (Ref. [3]). Note that RHESSI's hard X-ray footpoints neatly fit into the flare ribbon structures - just like SOL2000-07-14 where the concept of a "Bastille Day Flare" originated. The spectrum at flare maximum (right panel) shows soft and hard X-ray components consistent with our observations of similar events.

Figure 3: Left, RHESSI hard-ray image contours superposed on a background EUV image from AIA. Right, spectrum from flare peak (courtesy B. Dennis).

Conclusions

Is Bastille Day, over the decades, really a focus for major solar fireworks? This would be highly unlikely, and although we have cited four major events in 18 years here, that is not far from what one expect from a reasonable mean level of solar activity - about a 25% chance, per day, of seeing an M- or X-class flare. For RHESSI's first 11-year time span, the corresponding rate was 0.23 +- 0.03. So, no exceptionalism here.

A crude prediction for 2018 then, factoring in a guess at the solar-cycle dependence, suggests only about a 10% chance of another remarkable event next year - stay tuned to these pages and we will let you know then.

References

[1] "The Topology and Evolution of the Bastille Day Flare"

[2] "Large-scale Contraction and Subsequent Disruption of Coronal Loops During Various Phases of the M6.2 Flare Associated with the Confined Flux Rope Eruption"

[3] "Sigmoidal morphology and eruptive solar activity"

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