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Roger J Smith

Quiet Sun In Past Centuries

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Back in 2008, I posted a thread entitled "The Known History of Solar Activity" in the science thread. This thread is now locked, but you can still read it by going back in the science archives to June 2008.

If you remember that thread, I used the research of Schove as reported in Lamb's book on climate, Climate, Past, Present and Future published over thirty years ago now. The more recent data were added using the same criteria. Schove divided the peaks from his research into historical sunspot records and earlier, auroral records, into nine classes ranging from very weak to very strong.

What I've done here is to approach the question of periodic "quiet sun" episodes. In the earlier discussion, I made the point that solar activity has two basic modes, one being strong, regular activity with a period of about ten years, and a second being weaker, irregular activity with a period lengthening to twelve years. The Maunder mimumum represents an unusually long weak period. But what is the "normal" weak mode of solar activity like? How long does it last, and what are the chances of it being very weak, or just slightly weaker than "normal-strong" activity?

To study that, I take the same basic table of solar activity developed by Schove, and divide it into all evident periods that begin with strong, regular activity (because his record started that way) and then are followed by weak, irregular activity. This is somewhat subjective, of course, but my criteria for a strong period are that at least four cycles reach moderate (M) or higher, but may include single MW peaks as long as they do not repeat, and then the weak episode is taken to be whatever follows each of those, until regular service resumes. The Sporer minimum of the 15th century is maintained as a long minimum despite being borderline "strong regular" for part of its long duration. There are no other "strong" intervals that run this close to the criterion boundary, but since most scholars refer to this period as weak, I have included it (many of the peaks are MW-M).

This will give us a picture of the normal behaviour of both regular and weak modes of solar activity. One drawback will be that we have no sure way of knowing how long the Sun had been going strong when it hit the 290 AD peak that begins the record. The reader should note that this period may have been longer than shown here, it's just random that Schove could begin his continual records then (he has some discontinuous periods going back well into the 300 BCE century, but most of those are strong peaks).

Note in the dates below, the peaks are graphically represented, with each group of three dots representing one of the nine Schove intensity classes. These are WWW, WW, W, MW, M, MS, S, SS, SSS. You'll be able to verify that 290 was a "MS" peak meaning medium strong. Some idea of the actual intensity can be gained by comparing with familiar peaks in the recent past.

What I now show is the entire period of record, with each "strong" long-term modality identified at its end point, then each "weak" long-term modality identified at its end point. Although all other strong episodes require four or more peaks, the first one could have been going for any length of time prior to 290 and is ended after four peaks. The actual end of these periods should be taken as the mid-point between cycles following the entry in the graph. For example, the end-point of strong cycle A would be taken as 326 AD.

..................290

........................302

...............311

...............321 -- END OF STRONG "A" 3rd and early 4th centuries ....... 326

.........330

.........342 -- END OF WEAK "A" 4th century, lasted two cycles ............ 348 (22y)

.....................354

.....................362

........................372

...............387

...............396 -- END OF STRONG "B" late 4th century .................. 403 (55 y)

.........410

.........421 -- END OF WEAK "B" early 5th century, lasted 2 cycles ........ 426 (23y)

..................430

..................441

.....................452

.........465

..................479

...............490

........................501

.....................511

.........522

.....................531

...............542

...............557

........................567

...............578

.....................585 -- END OF STRONG "C" most of 5th and 6th centuries .... 591 (165y)

............597

.........607 -- END OF WEAK "C" around 600 AD .................................. 613 (22y)

...............618

............628

...............642

..................654

...............665

.....................677 -- END OF STRONG "D" mid-7th century ................... 683 (70y)

.........689

.........699 -- END OF WEAK "D" end of 7th century .............................. 707 (24y)

.....................714

.....................724

.........735

........................745

...............754

........................765

..................776

.........787

..................798

.....................809

.........821

.....................829

........................840

..................850

...............862

.....................872

...............887 -- END OF STRONG "E" lasting most of 8th and 9th centuries ..... 893 (186y)

.........898

.........907 -- END OF WEAK "E" around 900 AD ..................................... 912 (19y)

...............917

........................926

..................938

............950

........................963

........................974

...............986

.........994

.....................1003

...............1016

...............1027 -- END OF STRONG "F" 10th into early 11th centuries ........... 1033 (121y)

.........1038

......1052 -- END OF WEAK "F" mid-11th century .................................... 1060 (27y)

...............1067

...............1078

...............1088

........................1098

............1110

........................1118

.....................1129

........................1138

.....................1151

............1160

..................1173

..................1185

...............1193

........................1202

...............1219

...............1228

...............1239

............1249

...............1259

...............1276

...............1288

.........1296

...............1308

...............1319

...............1324 -- end of strong "G" most of 12th and 13th centuries to 1330 .... 1330 (270y)

.........1337

............1353 -- end of weak "G" mid-14th century ................................ 1358 (28y)

........................1362

...........................1372

..................1382

...............1391

...............1402 -- end of strong "H" late 14th century .......................... 1408 (50y)

......1413

............1429

............1439

............1449

............1461

......1472

......1480

............1497

.........1505 -- end of weak Sporer "H" most of 15th century ........................ 1512 (104y)

...............1519

........................1528

.....................1539

.....................1548

........................1558

........................1572

.....................1581

............1591

............1604

...............1615

..................1629

............1639 -- end of strong "I" most of 16th century to 1644 .................. 1644 (132y)

......1649

......1660

.........1675

......1685

...1693

......1705 -- end of weak "I" Maunder minimum late 17th century ..................... 1712 (68y)

.....................1718

........................1727

.....................1738

...............1750

...............1761

..................1769

........................1778

........................1787 -- end of strong "J" most of 18th century .............. 1796 (84y)

......1801

......1816

............1830 -- end of weak "J" Dalton minimum early 19th century ............... 1834 (38y)

........................1837

.....................1848

..................1860

........................1870 -- end of strong "K" mid-19th century .................. 1877 (43y)

.........1883

...............1893

.........1905 -- end of weak "K" around 1900 ........................................ 1911 (34y)

..................1917

...............1928

.....................1937

........................1947

...........................1957

..................1968

........................1979

........................1989

..................2001 -- end of strong "L" during most of 20th century ............ 2006 (95y)

????????????2013 -- could be start of new weak period.

I will post this and comment below.

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The above can be synthesized into the following chart of "strong" and "weak" modes of solar activity.

COUPLET STRONG (duration) WEAK (duration)

>>> A............. >40 ............ 22

>>> B.............. 55 ............ 23

>>> C............. 165 ............ 22

>>> D.............. 70 ............ 24

>>> E............. 186 ............ 19

>>> F............. 121 ............ 27

>>> G............. 270 ............ 28

>>> H ............. 50 ........... 104

>>> I .............132 ............ 68

>>> J ............. 84 ............ 38

>>> K ............. 43 ............ 34

>>> L ............. 95 (?) ........ (?)

Based on this count, and leaving out strong A, the averages are

AVG .............. 116 yrs ........ 37 yrs

If a shorter period is taken for the Sporer (the lower peaks from 1472 to 1491) this would alter the averages to about 122 yrs and 30 yrs.

The general conclusion here is that the modality is quite irregular. We can't even be totally sure that the 20th century strong-regular mode is over, by these criteria. However, what does jump out is that once the Sun subsides to medium-weak or lower activity, this usually lasts 2-3 cycles. The Sporer is one case of a longer weak period but only subsided to really weak activity for three cycles. The Maunder was unusually long in those terms, six cycles that fell below MW (and Schove may have been generous there).

What can be deduced from this analysis about the current postulated slowing of solar activity on the longer time scale? Mainly, that we need to be cautious about any conclusions at all. This long-term "Landscheidt" minimum could last two or three cycles, or longer, but we can't really be sure it has started at all. Note that some very long intervals qualified as "strong-regular" despite slowing down to one MW cycle. Each of the longer cases has one or two of these near the mid-way point. We can't be sure that postulated 2013 might not be just like that, and that regular activity will soon resume.

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Thanks for taking the time to do this.

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