Solar minimum surprisingly constant

Posted: November 18, 2017 by oldbrew in research, Solar physics, solar system dynamics
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It’s not known exactly what factors govern this constant minimum, but this is an interesting finding as Phys.org reports.

Using more than a half-century of observations, Japanese astronomers have discovered that the microwaves coming from the sun at the minimums of the past five solar cycles have been the same each time, despite large differences in the maximums of the cycles.

In Japan, continuous four-frequency solar microwave observations (1, 2, 3.75 and 9.4 GHz) began in 1957 at the Toyokawa Branch of the Research Institute of Atmospherics, Nagoya University. In 1994, the telescopes were relocated to NAOJ Nobeyama Campus, where they have continued observations up to the present.

A research group led by Masumi Shimojo, assistant professor at NAOJ Chile Observatory, including members from Nagoya University, Kyoto University, and Ibaraki University, analyzed the more than 60 years of solar microwave data from these telescopes. They found that microwave intensities and spectra at the minimums of the latest five cycles were the same every time. In contrast, during the periods of maximum solar activity, both the intensity and spectrum varied from cycle to cycle.

Masumi Shimojo says, “Other than sunspot observations, uniform long-term observations are rare in solar astronomy. It is very meaningful to discover a trend extending beyond a single solar cycle. This is an important step in understanding the creation and amplification of solar magnetic fields, which generate sunspots and other solar activity.”

The sun goes through a cycle of active and quiet periods approximately once every 11 years. This “solar cycle” is often associated with the number of sunspots, but there are other types of solar activity, as well. So simply counting the number of sunspots is insufficient to understand the solar activity conditions.

Microwaves are another indicator of solar activity. Microwaves, unlike sunspots, can be observed on cloudy days. Also, monitoring multiple frequencies of microwaves makes it possible to calculate the relative strength at each frequency (this is called the spectrum).

Source: Solar minimum surprisingly constant | Phys.org.

Study: Masumi Shimojo et al, Variation of the Solar Microwave Spectrum in the Last Half Century, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/aa8c75

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See also…
Daily Mail: The mystery of the solar minimum deepens as astronomers find it has remained ‘surprisingly constant’ for more than 60 years
[includes NASA ‘Solar Minimum’ video]

Comments
  1. Jim says:

    Interesting, but, i thought solar science was “settled science”, the 1 in earth heating. Now they are trying to tell me, that like I learned in the 60’s, that we live next to a variable star? And we can watch it! ” cause” it “ain’t” the same daily! Oh my!

  2. stpaulchuck says:

    “The science is settled.” “So what difference does it make?”
    two bald faced lies that just seemed to call to each other

  3. lsvalgaard says:

    This is not new nor surprising:
    We have known this for 150 years:

    and can be traced back to at least the 1740s:
    http://www.leif.org/research/Reconstruction-of-Solar-EUV-Flux-1740-2015.pdf

  4. oldbrew says:

    Variation of the Solar Microwave Spectrum in the Last Half Century
    Published 2017 October 12

    Abstract
    The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We examined the multi-frequency and long-term data sets, and found that not only the microwave solar flux but also its monthly standard deviation indicate the long-term variation of solar activity. Furthermore, we found that the microwave spectra at the solar minima of Cycles 20–24 agree with each other. These results show that the average atmospheric structure above the upper chromosphere in the quiet-Sun has not varied for half a century, and suggest that the energy input for atmospheric heating from the sub-photosphere to the corona have not changed in the quiet-Sun despite significantly differing strengths of magnetic activity in the last five solar cycles.

    http://iopscience.iop.org/article/10.3847/1538-4357/aa8c75/meta

    Dr Svalgaard’s linked pdf: ‘Reconstruction of Solar Extreme Ultraviolet Flux 1740–2015’ concludes (quoting from the abstract):
    The reconstruction suggests that the EUV flux reaches the same low (but non–zero) value at every sunspot minimum (possibly including Grand Minima), representing an invariant ‘solar magnetic ground state’.

  5. oldbrew says:

    NASA detects solar flare pulses at Sun and Earth

    Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses—an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales, and whether other solar flares induce this response.

    “This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”

    Read more at: http://phys.org/news/2017-11-nasa-solar-flare-pulses-sun.html

  6. J Martin says:

    The fact that EUV reaches a minimum is interesting, it would be more ntrsting to know if it drops below that during grand minima, though if it did it might not mean much as I suppose the energy input of EUV to the earth is not a significant contributor to ocean heat content.

    Leif, good to hear from you.

  7. gymnosperm says:

    Also glad to see Leif here. I was going to point out he has been saying there is a common floor for solar cycle minima long before the referenced study.

  8. oldbrew says:

    Of course the Sun does have variability, as each solar cycle is of a different length (within limits) and sunspots and solar flares, for example, are irregular.

    http://en.wikipedia.org/wiki/List_of_solar_cycles

  9. lsvalgaard says:

    As Loomis knew back in 1870…

  10. oldbrew says:

    WUWT just picked up on this ‘new discovery’…

    An indicator of rock bottom for the solar minimum
    Anthony Watts / 2 hours ago November 20, 2017

    Solar minimum surprisingly constant
    More than half a century of observation yields new discovery

    http://wattsupwiththat.com/2017/11/20/an-indicator-of-rock-bottom-of-the-solar-minimum/

    And soon got the ‘not new’ message from Dr S. (see above).