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How is "Latest X-Ray Event" Defined?


Guest John Golloway

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Guest John Golloway

Looking at a source like this one: http://www.swpc.noaa.gov/products/goes-x-ray-flux

 

How is the "latest x-ray event" defined? I have searched extensively for documentation on this point without success. Any help is appreciated!!

 

-there are many spikes on the chart which are ignored

-the largest spike is generally not the latest x-ray event

 

Perhaps an x-ray event is defined when the rate of x-ray increase crosses a certain threshold (the slope of the spike). If so, I have been unable to source information on what this threshold would be.

 

Thanks in advance SWL community!

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Hey John,

I also do not know any documentation on this subject. However, the latest solar flare (or spike) that they detected is always the one that is defined below. Not the largest. So below there in that box you will find the begin max and end time/data of the most recent solar flare. If there was an M1 solar flare 2 hours ago and a C3 solar flare just 1 hour ago you will see data of the C3 flare there.

If you scroll down here (http://www.spaceweatherlive.com/en/solar-activity) you will see all of the events of today thus far.

Hope this is of help.

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Guest John Golloway

Thank you for this information. 

 

If anyone has insight into the how an "x-ray event" is defined, I would appreciate it.

 

Thanks!

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You would have to ask NOAA as I do not know the exact definition of what classifies as a solar flare (event) for them but I would say a solar flare is defined by a clear peak in X-rays above the background flux in a reasonable time frame. That's all I can say, I wouldn't know how NOAA would describe it.

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Guest John Golloway

Thank you again!

 

I did submit this question to swpc.noaa.gov a few days ago. No response yet. I will update this thread for the group's general knowledge if I receive an answer.

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Guest John Golloway

Just following up to share the response that I receive from Rob at SWPC/NOAA. Comprehensive and very helpful. Thanks again to you Marcel.

 

From Rob:

 

The latest event is the latest X-ray flare automatically detected by the GOES 15 or GOES 14 satellite, or manually entered if the detection algorithm fails, without regard to any earlier events.  In other words, the "max" refers only to the maximum (peak) x-ray flux for the particular flare in question.  So, even though an M-class event may have occurred earlier, it will be supplanted by the next flare detected, even if the subsequent flare is only a C-class event.  The particulars for defining the begin, maximum, and end-time of an x-ray event is here, and excerpted below:

The begin time of an x-ray event is defined as the first minute, in a
sequence of 4 minutes, of steep monotonic increase in 0.1-0.8 nm flux.
The x-ray event maximum is taken as the minute of the peak x-ray flux.
The end time is the time when the flux level decays to a point halfway
between the maximum flux and the pre-flare background level.
 
Sometimes the algorithm will not trigger on a flare with a gradual rise-time (common for limb events), and the forecaster will have to enter the particulars manually.
 
In summary, latest may not always be the greatest.
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