Sixty+ Years of Solar Microwave Flux

Leif Svalgaard

Stanford University

SHINE 2010, Santa Fe, NM

Observations and Observatories• 1947.2-1991.5 Ottawa 2800 MHz (10.7 cm)• 1991.5-2010.5 Penticton 2800 MHz• 1951.8-1994.3 Toyokawa 3750 MHz (8 cm)• 1994.4-2010.5 Nobeyama 3750 MHz• 1957.4-1994.1 Toyokawa 2000 MHz (15 cm)• 1994.4-2010.5 Nobeyama 2000 MHz• 1957.2-1994.4 Toyokawa 1000 MHz (30 cm)• 1994.4-2010.5 Nobeyama 1000 MHz• 1956.3-1994.1 Toyokawa 9400 MHz (3.2 cm)• 1994.4-2010.5 Nobeyama 9400 MHz

All observations are highly correlated, especially the ones [2000, 3750] flanking 2800 MHZ

F2800 = 1.5707 F1000 - 0.9825

R2 = 0.9742

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F2800

F1000

1957-2010

F2800 = 1.177 F2000 + 6.6574

R2 = 0.9933

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F2800

F2000

1957-2010

F2800 = 1.1728 F3750 - 20.78

R2 = 0.9949

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F2800

F3750

1951-2010

F2800 = 1.4215 F9400 - 294.89

R2 = 0.9584

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2800

F9400

1956-2010

Monthly Averages

This allows us to scale all observations to 2800 MHz

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F9400

F3750

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Micro Wave Fluxes Scaled to 2800 MHz Flux

The scaled values match each other very well, except 9400 MHz where the solar activity component is rather noisy.

If the calibrations of the data have not changed over time, the ratios between the scaled fluxes and

the 2800 MHz flux should be constant = 1

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TYKW NBYM

OTWA PENT

Ratio between Scaled Japanese Flux and Canadian 2800 MHz Flux

Within the scatter, the ratios appear to be lower than 1 before 1991 and higher thereafter. We interpret that as a 2% downward jump in Pentiction compared to Ottawa. We therefore reduce the Ottawa 2800 MHz flux by 2%.

Same color associations as on previous Figure

After the correction, we rescale 2000 and 3750 MHz again to 2800 MHz, and construct a composite

F2800 = 4.56239E-06x3 - 7.93355E-04x2 + 1.13869E+00x + 1.10179E+01

R2 = 0.9939

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F2800*

F2000

1957-2010

F2800 = -8.49042E-06x3 + 3.71190E-03x2 + 6.45618E-01x + 1.50641E+00

R2 = 0.9955

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F3750

F2800* 1951-2010

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Composite F2800 MHz Solar Microwave Flux

Note how the minimum values do not vary with time (within green box)

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Cycle 18

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Cycle 19

Individual cycles

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Cycle 20

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Cycle 21

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Cycle 22

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Cycle 23

Cycle 24

There is a well-known, strong [slightly non-linear] relationship between the solar flux and the sunspot number (black diamonds). This relationship seems to have changed in solar cycle 23 (red circles).

y = 9.9392E-12x6 - 7.1116E-09x5 + 1.6776E-06x4 - 8.2748E-05x3 - 2.4487E-02x2 + 4.8162E+00x - 2.0983E+02

R2 = 0.97391

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1996-2010

Same conclusion reached by others, e.g. Tapping (2010)

Tapping, SORCE 2010

Plotting the reconstructed Sunspot Number (pink) from the composite 2800 MHz flux using the 1947-1990

relation shows the increasing discrepancy with the SIDC ‘official’ sunspot number (blue) the past ~15 years:

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Sunspot Number Observed and Reconstructed from Composite Flux Series

SSN Observed

SSN From 2800 Flux

As the Japanese and Canadian microwave data support each other so well, we must ask: how sure are we of the calibration and stability of the sunspot number?

Some other organizations that have kept a keen eye on the Sun, making

their own sunspot number series:ht t p: / / www. vds- sonne. de/ gem/ r es/ r esul t s. ht mlSIDC: Solar Influences Data Analysis Center, Brussels (International sunspot numbers)SONNE prov.: SONNE network, provisional sunspot numbers SONNE def. : SONNE network, definitive sunspot numbersAAVSO: American Association of Variable Star Observers - Solar DivisionAKS: Arbeitskreis Sonne des Kulturbundes e.V., GermanyBAA: The British Astronomical Association - Solar Section, UKGFOES: G.F.O.E.S. Commission "Nombre de Wolf", FranceGSRSI: GruppoSole Ricerce Solari Italia, ItalyOAA: The Oriental Astronomical Association - Solar Division, JapanRWG: Rudolf Wolf Gesellschaft - Solar Obs. Group of Swiss Astron. SocietyTOS: Towarzystwo Obserwatorow Slonca - Solar Observers Society, PolandVVS: Vereniging voor Sterrenkunde, Werkgroep Zon, Belgium

All these series can be successfully scaled to SIDC before August 2001

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SIDC

RSONNE AAVSO AKS BAA GFOES GSRSI OAA RWG TOS VVS

But the same scaling relation yields a sunspot number after that time that is systematically 12% higher than SIDC’s. Did all these organizations somehow change their procedures and/or or observer cadre? Or did SIDC?

It seems that we increasingly see ‘fewer spots’ for the same amount of microwave flux. We can quantify that by the

ratio between observed spots and expected spots from the pre-1991 relationship:

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?

Ratio of Observed Sunspot Number to Simulated SSN

Zurich SIDC

+12% correction

Monthly means when R>4

Adding 12% [assuming that SIDC has a problem in August 2001] does not materially alter this conclusion (red crosses).

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1B Gauss Intensity

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Livingston & Penn Umbral Data Measurements

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B Gauss

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Livingston & Penn Umbral Magnetic Field Measurements

Are there other indications of lesser visibility of sunspots?

Livingston and Penn report a decrease of magnetic field strength and hence decrease in contrast (less dark) with the surrounding photosphere.

Is this discrepancy another one?