Jul 2012 CME impact on Stereo-A

[tniickck]

 

2 minutes ago, Philalethes said:

I actually delved a bit into it myself to see what I could find, and those findings agree with what you're saying (and also resolves any ambiguity about whether the flare strength was estimated from our view or from the SA imagery).

For you or anyone else interested I first checked the Wikipedia page on the Solar storm where I first found the claim about it being maximum X2.5, which says:

So I checked the citation, and located the full article here, where it says:

This finally led to the article being cited there, which is titled Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images, in other words exactly what I was wondering if there existed a way to do; they conclude that their estimates should be fairly accurate for stronger flares (>M4), and list several events in a table there, including the one in question:

 

Just wanted to add that Carrington flare was X45. you made a nice research! 

[Philalethes]

1 hour ago, tniickck said:

Just wanted to add that Carrington flare was X45. you made a nice research! 

Yeah, I guess we know where the X2.5 estimate comes from at least.

As for the Carrington flare, we don't really know, but I'm aware of the ~X45 estimate (although as mentioned below I believe today that would be ~X64 after rescaling); I believe the article simply put down >X10 to avoid making any assumptions while still making it clear that it was a very intense flare.

I've seen a few different estimates, but generally they agree more or less with an intensity around those parts. Here are a couple of others; first this one:

Quote

We estimate the Carrington flare to be no less than ~X15 and believe that it is more likely to be ~X42. It is important to note that small deviations in both the geomagnetic latitude and in the scaling result in large deviations in the predicted X-ray flux.

This is near the original ~X45 estimate (I believe that paper was published before the rescaling), but does highlight that there's a lot of potential variability involved. It's also worth noting that it's only basing the estimate on the effects here on Earth.

And this is another interesting one, which claims to be the first rigorous estimate based on the only direct observation of the flare itself:

Quote

To date, no rigorous estimate of the energy of this flare has been made on the basis of the only direct observation available, its white-light emission. Here, we exploit the historical observations to obtain a magnitude estimate and express it in terms of its GOES soft X-ray class. From Carrington's original drawings, we estimated the area of the white-light flaring region to be 116 ± 25 msh. Carrington's account allows us to estimate the flare blackbody brightness temperature as ≈8800-10,900 K, given the most plausible interpretation of the reported flare brightness. This leads to an unprecedented class estimate of ≈X80 (X46-X126), on the modern revised GOES scale (a factor 1.43 higher than the traditional one). This substantially exceeds earlier estimates but is based on an explicit interpretation of Carrington's description. [...] Approximations with "equivalent area," based on the Hinode observations, lead to comparable magnitudes and approve our estimates, though with a larger uncertainty range. We note that our preferred estimate is higher than the currently used value of X64.4 ± 7.2 (revised) based on indirect geomagnetic measurements.

The second part I've highlighted with bold also references an interesting fact, because it directly references the paper that gave the ~X45 estimate that has been widely taken for granted; with the current GOES scaling that estimate is actually ~X64. As they write in the introduction:

Quote

To date, the magnitude of the Carrington flare has been indirectly estimated as a GOES magnitude of ≈X45 ± 5 (and subsequently revised to X64.4 ± 7.2 owing to the GOES rescaling), based mainly on contemporary geomagnetic measurements for synchronized solar flare effects.

As for the estimate of this paper itself it's interesting that it's even higher, albeit with a lot of uncertainty, but of course going by some ancient drawings and descriptions of the observation by a single person (well, two including Hodgson) has its own caveats, and is based on a lot of assumptions. Just for reference, to compare it to the unscaled ~X45 estimate this ~X80 estimate would be an estimate of ~X56 if using the same old scale instead of the rescaling, so it's not that far off.

Also for reference is the paper that provided the ~X45 estimate, which was published in 2013 (before the GOES rescaling):

Quote

In response to new research on the 1859 solar-terrestrial event since the survey by Cliver & Svalgaard (2004), we updated our assessment of this remarkable event. In the intervening years, the estimate of the size of the flare has been refined from “conservatively >X10” to ~X45 (±5) [...]

This also mentions the more conservative estimate from 2004 by the same author (Cliver) of >X10, so maybe that's where the estimate in the paper from the above post was taken from; it was published in 2013, same as the estimate above, so wouldn't be too surprising if they just went with a more conservative estimate that had been around for a while at that point.

I guess I should really have taken this to yet a different thread, heh; I suppose we can continue in some thread for the Carrington event for further discussion, I'm sure there are some of those lying around.

Edited February 6 by Philalethes
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