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Solar cycle and CMEs


Robert

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Hi All-

I am new to this subject, and apologize if this question has been addressed elsewhere. 

In this 2015 UK Space Weather Preparedness Strategy report, on page 8, it claims:
"There is no evidence for the likelihood of severe space weather to vary with the solar cycle. Indeed, our reasonable worst case scenario, the Carrington Event (see section 2.2 below), happened during the lowest part of the cycle."

Is this correct?

Again, my knowledge is close to zero . . . but this seems to contradict my basic notion (perhaps wrong) that more sunspots = higher probability of solar flares / CMEs

Also, the point about the Carrington Event happening during a solar minimum just seems like poor statistical logic. Just because a 1% probability event happens during a solar minimum doesn't seem to tell us much about the relative probabilities of occurring during a solar maximum. Sample size is way too low to draw any inference here. 

Would be grateful for your help and guidance!

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There have been instances where large solar storms and geomagnetic storms have happened during solar minimum, but most of the large storms happen around solar maximum when there are the most sunspots and they are at the largest and most complex. About the Carrington Event, that happened right before solar maximum where solar activity was already near cycle peak.

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2 hours ago, Robert said:

Is this correct?

It is incorrect. Carrington event took place in September 1859, and solar cycle 10 maximum took place in February 1860, so it took place only 5 months before the maximum.

We only have one confirmed Carrington event in 1859 and a possible one in 774 AD. The frequency could be lower than one per millennium. Nothing to lose sleep about. But good to know that in the UK are ready even if it happens during this solar minimum ;)

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More sunspots do not necessarily mean that there are more chances for solar flares and/or CME's. First of all, a sunspot region has to develop a complex magnetic structure (see help --> magnetic classification of sunspots) which pose a threat for strong solar flares. If a region develops a magnetic delta structure, the odds for a strong solar flare get higher. But then there are two possible outcomes: short lived moderate to strong solar flares without CME's and long duration solar flare events with an associated CME. I've seen very complex regions that stayed quiet, have seen regions that are sputtering with short lived solar flares that barely have effect and I've seen the major solar events like the ones of the halloween event (2003). I just want to point out that the numbers don't matter, it's the complexity of the region that gives its potential. You can have one huge complex sunspot region that's capable of strong events with no other regions on the visible disk (or just some other regions with a simple magnetic structure).

Also of note, even if a CME is associated with a very strong event, the location on the visible solar disk is also important. If the region is at the limb, we won't see much of it. In SC24 we have had several occasions on the far side of the sun where we've seen massive backside CME's which of course had no impact at Earth. We only see and measure what's visible on the disk 😉 

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6 hours ago, Vancanneyt Sander said:

More sunspots do not necessarily mean that there are more chances for solar flares and/or CME's.

As a matter of fact, they do. If one considers the evolution from a spotless sun to a flare/CME, it is necessary for a sunspot to be present for any further progress to be made towards the flare/CME, just as with Hurricanes/Cyclones/Typhoons and their tropical origins as broad troughs of low pressure. While not every low-pressure over the ocean develops into a tropical storm or worse, it is still vastly more likely for one to form in such a way than a storm forming over a dry land- and air-mass. So, in that sense, a sunspot at least has a fleeting chance of becoming complex, whereas a spotless region hasn't even been fertilized yet.

Since the factors for a sunspot developing into something significant(to us) are more constrained by mesoscale conditions, and less by the macroscale(solar cycle, for instance), it makes sense to see the periods of high solar activity as more likely to develop a sunspot that does something, but as Sander points out, it doesn't have an effect on the likelihood of a flare/CME on a per-sunspot basis.

In shorter, layman terms, if you buy 5 lottery tickets instead of 1, your odds are the same for each individual ticket, but since you have 5 of them, you're 5x as likely to win with 1 of them.

Edited by Christopher S.
I had "more" and "less" switched around
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Doesn't the strength of Earth's magnetosphere have some influence on how the CME/solar wind impacts earth?  My understanding is that during solar minimum our "shields" are weaker and any incoming space weather directed at us is less likely to be diverted.

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6 hours ago, Capricopia said:

Doesn't the strength of Earth's magnetosphere have some influence on how the CME/solar wind impacts earth?  My understanding is that during solar minimum our "shields" are weaker and any incoming space weather directed at us is less likely to be diverted.

I think you're confusing that with Cosmic Rays and the Interplanetary Magnetic Field. During solar minimum, the IMF is a bit weaker and Cosmic Rays have an easier time reaching us - these are radioactive particles at various wavelengths that travel from distant/nearby stars. More solar wind during higher periods of solar activity act to deflect the bulk of these.

The Earth's own magnetosphere is actually quite regular during a minimum, as stronger solar winds only arrive from coronal holes and the rare flare/CME. It is kept active by a dynamo effect within the planet's interior, and that isn't going to ever cease in our lifetimes. It persists regardless of the period in the solar cycle.

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If p=probability of a single lottery ticket being a winner, then the probability of at least 1 in 5 lottery tickets being a winner=1-(1-p)^5.  This falls in the "At least one" probability problem category which makes use of the probability complement rule P(A) = 100% − P(not A).  https://www.stat.berkeley.edu/~stark/SticiGui/Text/probabilityAxioms.htm

A team of researchers from Japan have tried to figure out how to predict solar flares automatically based on feature extraction and tracking of active sunspot regions.

https://ui.adsabs.harvard.edu/abs/2018ApJ...858..113N/abstract

In the introduction they note "It is empirically known that larger sunspots with a large number of umbra and a more complicated magnetic flux structure tend to produce larger flares."

They've churned through 300,000 SDO images from the first half of solar cycle 24 in developing and training their neural net machine learning algorithms.  Each active region of sunspots is tracked with 79 features extracted for each.   If a flare occurs within 24 hours of being predicted by the algorithms it is tallyed as a "True Positive" (correct 63% for C-class or higher, 80% for M-class or higher.)  However, there are many "False Positives."

They indicate that their algorithm does a better job of solar flare prediction than human operators.

Edited by Drax Spacex
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1 hour ago, Drax Spacex said:

If p=probability of a single lottery ticket being a winner, then the probability of at least 1 in 5 lottery tickets being a winner=1-(1-p)^5.  This falls in the "At least one" probability problem category which makes use of the probability complement rule P(A) = 100% − P(not A).  https://www.stat.berkeley.edu/~stark/SticiGui/Text/probabilityAxioms.htm

A team of researchers from Japan have tried to figure out how to predict solar flares automatically based on feature extraction and tracking of active sunspot regions.

https://ui.adsabs.harvard.edu/abs/2018ApJ...858..113N/abstract

In the introduction they note "It is empirically known that larger sunspots with a large number of umbra and a more complicated magnetic flux structure tend to produce larger flares."

They've churned through 300,000 SDO images from the first half of solar cycle 24 in developing and training their neural net machine learning algorithms.  Each active region of sunspots is tracked with 79 features extracted for each.   If a flare occurs within 24 hours of being predicted by the algorithms it is tallyed as a "True Positive" (correct 63% for C-class or higher, 80% for M-class or higher.)  However, there are many "False Positives."

They indicate that their algorithm does a better job of solar flare prediction than human operators.

I see what you're saying, but you're vastly overthinking the example I made.

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From the Spaceweatherlive help section:  "Delta groups are formed by the aggregation of sunspots with opposite polarity of various dipoles, which are linked to shared magnetic field lines rather than direct magnetic lines."

One can visualize why delta sunspot groups would be more likely to give rise to large solar flares.  One of the actions of sunspots is to hold tight to the ends of the hoop-like flux ropes.  These flux ropes might be considered analogous to the patterns of iron filings near one or more  magnets.  In a bipolar sunspot group, North and South Poles create strong, tight magnetic fields that hold the flux ropes ends to the surface of the sun .   But in a Delta sunspot group, the additional magnetic poles, unevenly distributed in spacing and polarity, complicate the magnetic field and may introduce field nulls (or local minima).

With so much energy stored, when the magnetic fields morph in such a way that those cords binding the flux ropes become loosened, even for a short time, that can initiate a solar flare and/or CME.

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