Solar Cycle 24 Main Discussion IX

[Bob k6tr]

Sept 29, 2010 6:48:46 GMT lsvalgaard said:

Sept 29, 2010 4:15:58 GMT fredfriendly said:

Leif-

Will the average remain 10 if we are entering a solar minimum? Won't the use of this "average" just skew the number? Why use the "average" and the sunspot number? ?If each group "averages" ten then lest just take each group and multiply by ten. The whole argument seems internally inconsistent and skews numbers upward at low group numbers...as at the beginning and end of cycles the group numbers sure seem to "average" less than ten spots...

Experience shows that the sunspot number also works well at minimum. There is also a Group Sunspot Number that is defined as 12*Number of Groups. The two sunspot numbers agree quite well in annual means [not, of course, on every single day]. We have more than 150 years experience with this and have found that the scheme works well enough to still be useful.
That said, there is evidence that the scheme may be breaking down. See, e.g. www.leif.org/research/SIDC-Seminar-14Sept.pdf
This may have happened before, e.g. during the Maunder Minimum, explaining why few sunspots were seen, e.g. www.leif.org/research/Does%20The%20Sun%20Vary%20Enough.pdf

Speaking of schemes breaking down have you noticed this ?

Last week was the first time I can remember this cycle that we had two spot groups on the visible face of the sun with sizable penumbra. What I found interesting was the 304A reading during that time period was NOT near record high readings. As a matter of fact it was actually declining ! Checkout umtof.umd.edu/sem/ from Sept 23 to Sept 27. Fourth chart from the top. The red trace. During that time 1109 was growing very fast adding both number and size of spots. Yet there was no corresponding increase in 304A measurement. Is there an explanation for this ? Is anyone studying it ?

[lsvalgaard]

Sept 29, 2010 17:29:52 GMT Bob k6tr said:

Sept 29, 2010 6:48:46 GMT lsvalgaard said:

Experience shows that the sunspot number also works well at minimum. There is also a Group Sunspot Number that is defined as 12*Number of Groups. The two sunspot numbers agree quite well in annual means [not, of course, on every single day]. We have more than 150 years experience with this and have found that the scheme works well enough to still be useful.
That said, there is evidence that the scheme may be breaking down. See, e.g. www.leif.org/research/SIDC-Seminar-14Sept.pdf
This may have happened before, e.g. during the Maunder Minimum, explaining why few sunspots were seen, e.g. www.leif.org/research/Does%20The%20Sun%20Vary%20Enough.pdf

Speaking of schemes breaking down have you noticed this ?

Last week was the first time I can remember this cycle that we had two spot groups on the visible face of the sun with sizable penumbra. What I found interesting was the 304A reading during that time period was NOT near record high readings. As a matter of fact it was actually declining ! Checkout umtof.umd.edu/sem/ from Sept 23 to Sept 27. Fourth chart from the top. The red trace. During that time 1109 was growing very fast adding both number and size of spots. Yet there was no corresponding increase in 304A measurement. Is there an explanation for this ? Is anyone studying it ?

The Sun is a messy place. Only when several such cases become apparent will anybody look into it.

[Bob k6tr]

There is a magnetic signature growing at a healthy clip in the Southern Hemisphere. It is located near the same Longitude Line as 1109. It does not have any spots right now but should soon. It will be nip-and-tuck if those spots form in time to be visible during the 0000 UTC SWPC Observation.

[Kevin VE3EN]

Sept 29, 2010 23:18:34 GMT Bob k6tr said:

There is a magnetic signature growing at a healthy clip in the Southern Hemisphere. It is located near the same Longitude Line as 1109. It does not have any spots right now but should soon. It will be nip-and-tuck if those spots form in time to be visible during the 0000 UTC SWPC Observation.

Oh so tiny...

[af4ex]

k6tr wrote:
> What I found interesting was the 304A reading during that
> time period was NOT near record high readings. As a matter o
> f fact it was actually declining !

I have a couple of questions about this. (trying to understand 304A)
1. Why did you expect the 304A reading to have a record high?
2. Is this reading based on a full-disc average of 304A emissions?
3. Looking at the 304A EUV imagery, the brightest activity seems to always coincide with sunspots.
Is this always the case? Are there 304A "events" that are not associated with sunspots?

If it's sunspots causing the 304A signal to jump, then looking for changes in overall 304A brightness seems inefficient. In visible light wouldn't that be equivalent to looking for overall darkening caused by sunspots?

Or am I overlooking some other mechanism gernerating these signals?

Thanks,
John/af4ex

[Bob k6tr]

Sept 30, 2010 3:59:50 GMT Kevin VE3EN said:

Sept 29, 2010 23:18:34 GMT Bob k6tr said:

There is a magnetic signature growing at a healthy clip in the Southern Hemisphere. It is located near the same Longitude Line as 1109. It does not have any spots right now but should soon. It will be nip-and-tuck if those spots form in time to be visible during the 0000 UTC SWPC Observation.

Oh so tiny...

Yup....it looks like it ran out of gas.


Oh well.......only one other thing to do.....NEXT !

[Bob k6tr]

Sept 30, 2010 10:36:24 GMT af4ex said:

k6tr wrote:
> What I found interesting was the 304A reading during that
> time period was NOT near record high readings. As a matter o
> f fact it was actually declining !

I have a couple of questions about this. (trying to understand 304A)
1. Why did you expect the 304A reading to have a record high?
2. Is this reading based on a full-disc average of 304A emissions?
3. Looking at the 304A EUV imagery, the brightest activity seems to always coincide with sunspots.
Is this always the case? Are there 304A "events" that are not associated with sunspots?

If it's sunspots causing the 304A signal to jump, then looking for changes in overall 304A brightness seems inefficient. In visible light wouldn't that be equivalent to looking for overall darkening caused by sunspots?

Or am I overlooking some other mechanism gernerating these signals?

Thanks,
John/af4ex

1) Because 304A is part of the radiative spectrum of a Sunspot. It would follow that if the magnetic portion of the spot had grown to unprecedeneted levels 304A radiation ould follow.

2) It is not an average but a cumulative figure.

3) I know of no other solar phenomenon that increases 304A radiation beyond the backround level.

Regarding your last set of questions. My personal interest about the 304A number is related to Ionospheric MUF Predictions. We know that the MUF rises as the sunspot number increases. The same can be said for the 10.7 cm Solar Flux. But there are times when the SFI rises with little corresponding increase in MUF. Reading through a number of papers and following ARRL Propagation indicates that 304A numbers give a tighter correlation. As has already been discussed here an actual sunspot doesn't form until the intensity of a magnetic area exceeds 1500 gauss. But the 304A number provides detectable measurements within a few hours after the appearance of a magnetic region. Casual observation over the last 9 months reveals that the 304A, SFI and Sunspot Number do not move in unison. Therefore it appears the 304A number furnishes a more reliable index from which to make MUF Predictions than SFI or Sunspot Number.

In the grand scheme of things if others where making measurements of other spectra emitted by sunspots the way Bill Livingston is tracking magnetic radiation it might yield some useful information into understanding the dynamics behind sunspot formation.

[af4ex]

k6tr wrote:
> Therefore it appears the 304A number furnishes a more
> reliable index from which to make MUF Predictions than SFI
> or Sunspot Number.

Ok, I did a little Googling and now I think I see why 304A is so important for MUF modeling. EUV plays a part in F2 ionization. 304A must be one of the more active wavelengths in ionospheric ionization, right?

So I think I was jumping to the wrong conclusion here:
>> If it's sunspots causing the 304A signal to jump, then looking for
>> changes in overall 304A brightness seems inefficient.

I see now that for propagation purposes we don't care where the 304A comes from, sunspots or other regions, as long as it stirs up the ionosphere. So the accumulative reading is more useful than trying to compute contrast ratios etc.

One more question: I see that SC24.com gets the 304A reading from N0NBH, but he displays a completely different value. Right now the values are:
SC24: 304A=226 @ EVE
N0NBH: 304A=127.8 @ SEM

Are these expressed in different units of measurement? What does 'EVE' and 'SEM' stand for?

Thanks,
John/af4ex

[Bob k6tr]

Oct 1, 2010 1:40:20 GMT af4ex said:

k6tr wrote:
> Therefore it appears the 304A number furnishes a more
> reliable index from which to make MUF Predictions than SFI
> or Sunspot Number.

Ok, I did a little Googling and now I think I see why 304A is so important for MUF modeling. EUV plays a part in F2 ionization. 304A must be one of the more active wavelengths in ionospheric ionization, right?

So I think I was jumping to the wrong conclusion here:
>> If it's sunspots causing the 304A signal to jump, then looking for
>> changes in overall 304A brightness seems inefficient.

I see now that for propagation purposes we don't care where the 304A comes from, sunspots or other regions, as long as it stirs up the ionosphere. So the accumulative reading is more useful than trying to compute contrast ratios etc.

One more question: I see that SC24.com gets the 304A reading from N0NBH, but he displays a completely different value. Right now the values are:
SC24: 304A=226 @ EVE
N0NBH: 304A=127.8 @ SEM

Are these expressed in different units of measurement? What does 'EVE' and 'SEM' stand for?

Thanks,
John/af4ex

1) Yes, about 25 to 50 percent of the energy that goes into ionoizing the F Layer comes from the 304A spectral line

2) I can't say a cumulative value is more useful but it is just as useful for our purposes and certainly easier to gather. The work that Bill Livingston is doing in the magnetic range is very tedious.

3)EVE and SEM are the two instruments carried aboard Solar Satellites that measure 304A spectrum. SEM rides aboard SOHO and EVE aboard SDO. There is historical data for SEM but none for EVE. We are in the process of harmonizing the two scales.

[france]

And can we get acces to historical data for SEM ?

[france]

Sept 29, 2010 17:29:52 GMT Bob k6tr said:

Speaking of schemes breaking down have you noticed this ?

Last week was the first time I can remember this cycle that we had two spot groups on the visible face of the sun with sizable penumbra. What I found interesting was the 304A reading during that time period was NOT near record high readings. As a matter of fact it was actually declining ! Checkout umtof.umd.edu/sem/ from Sept 23 to Sept 27. Fourth chart from the top. The red trace. During that time 1109 was growing very fast adding both number and size of spots. Yet there was no corresponding increase in 304A measurement. Is there an explanation for this ? Is anyone studying it ?

My suggestion : 304A measurement was probably "compressed" by the wind of the coronal hole. But it'll possible the orientation of the spacecraft favoured this "atypical" measure. spaceweather.com/archive.php?view=1&day=28&month=09&year=2010

[af4ex]

France said:
> My suggestion : 304A measurement was probably compressed by the
> wind of the coronal hole.

The umd link suggests that the 304A channel (Ch4) picks up 'interference' (QRN in Ham lingo) from other wavelengths, including energetic particles. Is that what you mean by 'compression'?

The top panel ("ch4") is the first-order SEM channel with a passband of 304 +- 40 Angstroms. This channel responds primarily to the very strong Helium 304 line, but is also sensitive to some 'hotter' lines (i.e., lines enhanced during solar events) in its passband, and can also be sensitive to background produced by energetic flare particles. For a rough indicator of the current flare background, see our PM flare plot.

[france]

Oct 1, 2010 10:45:56 GMT af4ex said:

France said:
> My suggestion : 304A measurement was probably compressed by the
> wind of the coronal hole.

The umd link suggests that the 304A channel (Ch4) picks up 'interference' (QRN in Ham lingo) from other wavelengths, including energetic particles. Is that what you mean by 'compression'?

The top panel ("ch4") is the first-order SEM channel with a passband of 304 +- 40 Angstroms. This channel responds primarily to the very strong Helium 304 line, but is also sensitive to some 'hotter' lines (i.e., lines enhanced during solar events) in its passband, and can also be sensitive to background produced by energetic flare particles. For a rough indicator of the current flare background, see our PM flare plot.

Of course, I thought it was a scientific term.

where is the umd link ?

[af4ex]

> Of course, I thought it was a scientific term.

France,
In information theory it means reducing the size of information. In solar physics I don't know what it means.

So it wasn't clear whether you meant some physical interaction between 304A photons and solar wind, e.g. similar to the way solar wind interacts with cosmic rays. Or, if you meant some artifact of detection in the sensor, e.g. reduction in SNR due to QRN or pointing errors etc.

So, you meant the latter, or something else?
:-]

[af4ex]

> where is the umd link ?
It was mentioned in k6tr's original post:
umtof.umd.edu/sem/