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To what extent do the levels of UVA, UVB and UVC radiations on the earth surface increase during solar flares?

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    $\begingroup$ I know you're asking for the effects on the Earth, but as the source of the radiations is the star, it might be worth asking at the Astronomy SE: astronomy.stackexchange.com $\endgroup$
    – Jean-Marie Prival
    Jan 30, 2020 at 10:10
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    $\begingroup$ To my limited knowledge UV radiation does not change much on earth's surface. Depending on type and intensity of a CME, x- and gamma-rays as well as charged particles can influence the upper atmopshere. But i do not know to what extent The astronomers are a good place to ask, i think too. $\endgroup$
    – user18607
    Jan 30, 2020 at 11:41
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    $\begingroup$ I believe that UV from the Sun is essentially all thermal: the Sun emits UV because it's hot enough and the blackbody spectrum extends into the UV. If that's true then changes in UV would correspond to changes in the surface temperature of parts of the Sun during the flare. I suspect those changes are small. $\endgroup$
    – user18801
    Jan 30, 2020 at 14:19
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    $\begingroup$ agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005JA011507 $\endgroup$
    – trond hansen
    Jan 30, 2020 at 15:10

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During a powerful solar flare the amount of x-ray radiation can increase up to 110% in the boundry layer of the atmosphere/space,very little of this will reach the earths surface but it can be measured from high flying planes.

UVC is stopped by the upper layer of the atmosphere so this will never reach the ground,It might be possible to measure some UVC in antarctica because of the ozone hole but it is very weak so one will need special equipment to measure it.

UVB will change very little during a solar flare and only in the shortest wavelenght of the UVB spectrum will additional radiation be measurable.

UVA radiation will not change at ground level.

During a solar flare only the shorter wavelenghts of the electromagnetic spectrum will be affected,hard x-rays the most and the longer wavelenghts will be less affected.

source https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005JA011507

source for more detailed information https://en.wikipedia.org/wiki/Ultraviolet

enter image description here

i do not have the source for this picture but i think it is free to use.

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    $\begingroup$ The image appears to be from John Emmert of the Navy Research Lab -- as it's a US govt institution it should be free to use. $\endgroup$
    – MrAzzaman
    Jan 31, 2020 at 8:52
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Solar flares are very variable in size and position. A small one on the edge of the sun's disc would have no effect on Earth, but I presume you mean a large one. UVC would be stopped by the ozone layer, so no increase there. UVB gets through the atmosphere with difficulty, so there might be a small increase there, but nothing to worry about. The atmosphere is completely transparent to UVA, so there could be a significant increase with a very large flare. You wouldn't know this unless you followed the TV weather announcements of ultra-violet hazard. If it happened to be cold and wet in your part of the world it wouldn't affect you unless you were in the habit of sunbathing in single-figure temperatures, lowering cloud and pouring rain. Not many people do this.

More worrying for most people would be the flare's effect on satellites and communications, or even to the electricity grid in the event of a really large coronal mass ejection. The arrival of huge amounts of charged particles emitted by a flare creates electric currents in the atmosphere which in the most severe cases have been known to shut down electricity grids for many hours.

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    $\begingroup$ Pls. provide source for your assertions so that it is of use to the community. $\endgroup$
    – user18607
    Jan 30, 2020 at 11:30
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    $\begingroup$ The question asks for an extent of increase, so the answer should be at least semi-quantitative, like an order of magnitude (backed with a reference of course, as usual when giving numbers). $\endgroup$
    – Jean-Marie Prival
    Jan 30, 2020 at 12:27
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    $\begingroup$ Well I think OP deserves more than general recitations and "watch the tv". It is not that simple ncbi.nlm.nih.gov/pmc/articles/PMC4516105 and e.g. flightsafety.org/asw-article/flare-ups. A more differentiated view would be really nice. $\endgroup$
    – user18607
    Jan 30, 2020 at 12:29
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    $\begingroup$ michael i have flagged your answer as very low quality,this is obviously a field you know very little about.please stop spamming our site with low quality answers. $\endgroup$
    – trond hansen
    Jan 30, 2020 at 14:54

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