Multi-Instrument Solar Flare Observations II: A SC24 retrospective
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Contents |
Introduction
Using the search capabilities outlines in a previous nugget, we can now do a retrospective analysis to see how effective our coordinated observations - either planned or serendipitous - have been during Solar Cycle 24. We consider the first 6.5 years after SDO was launched (1 May 2010-31 Oct 2016), which encompasses the peak of Solar Cycle 24 (vertical dotted lines in Figure 1).
Statistics
First we shall take a look at how instrument performed individually. Table 1 shows the breakdown of flares listed in the SSW Latest Events catalog (by class) observed by each instrument. Note that MEGS-A had a 100% duty cycle up until 26 May 2014 when it suffered a power anomaly. Similarly, IRIS was only launched on 27 June 2013 so only flares after this date (in parentheses) were considered.
Instrument/Database | C-class | M-class | X-class | Total | Success Rate |
SSW Latest Events | 6,339 | 581 | 33 | 6,953 | N/A |
---|---|---|---|---|---|
RHESSI | 3,673 | 370 | 23 | 4,066 | 58% |
SDO/EVE MEGS-A | 3,825 | 343 | 19 | 4,187 | 100% |
SDO/EVE MEGS-B | 787 | 97 | 8 | 892 | 12% |
Hinode/EIS | 496 | 54 | 6 | 556 | 8% |
Hinode/SOT | 1,167 | 177 | 15 | 1,359 | 20% |
Hinode/XRT | 3,793 | 357 | 26 | 4,122 | 59% |
IRIS | 523 (3,349) | 76 (335) | 5 (16) | 604 (3,700) | 16% |
Now we look at how many flares (of all classes) were observed by various combinations (degree) of instruments. Again note that all 7 instruments were only operational together for 11 months, and the number of flares duration this time are given in parentheses. From this we can calculate that - on average - each flare was observed by 2.4 instruments.
Degree | Number of flares observed | % of potentially observable flares |
No instrument | 127 | 1.8% |
Only 1 instrument | 1,432 | 20.6% |
2 instruments | 2,371 | 34.1% |
3 instruments | 2,035 | 29.2 |
4 instruments | 720 | 10.3% |
5 instruments | 228 | 3.3% |
6 instruments | 37 | 0.5% |
All 7 instruments | 3 (934) | 0.3% |
UpSetR plots
To help visualize these relationships we have used UpSet (Ref 1), a novel tool for visualizing intersecting datasets. This type of plot enables the efficient visualization the common elements of a large number of sets (the more common and familiar Venn diagram approach produces ineffective visualizations). The left hand panel of Figure 2 shows the intersections of the various combinations of dataset ordered by decreasing frequency (i.e. the most common combinations are on the left and decrease towards the right). The right hand panel shows the same information only now ordered by increasing degree (i.e. flares observed by individual instruments alone come first, with flares observed by all seven on the far right). In each figure, the total number of flares observed by each instrument are given by the horizontal black bars in the bottom left corner. The dots connected by lines at the bottom of each figure denote the combinations of instruments considered, while the histograms above give the number of events corresponding to a given combination. The most common combination of flare datasets was RHESSI+MEGS-A+Hinode/XRT (930 flares), due to their large fields of view and high duty cycles.
Conclusions
The paucity of events co-observed by multiple, complementary instruments points to the challenge of observing solar flares in flagrente delicto. Without a reliable method of predicting when and where a solar flare will occur, we are left with trying to optimize instrumental resources in the face of incomplete information as well as each instruments' operational constraints and competing scientific priorities. This is worth bearing in mind as we approach Solar Cycle 25, and the advent of the Daniel K. Inoue Solar Telescope, Solar Orbiter and Solar Probe Plus.
Biographical Note
Ryan Milligan is currently an Ernest Rutherford Fellow at the University of Glasgow.