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    Solar Activity: Smallest Sunspot Cycle Since 1906
    By News Staff | September 19th 2013 07:40 AM | 4 comments | Print | E-mail | Track Comments
    Predicting the behavior of a sunspot cycle is fairly reliable once the cycle is well underway (about 3 years after the minimum in sunspot number occurs(1). Prior to that time the predictions are less reliable but planning for satellite orbits and space missions often require knowledge of solar activity levels years in advance.

    A number of techniques are used to predict the amplitude of a cycle during the time near and before sunspot minimum. Relationships have been found between the size of the next cycle maximum and the length of the previous cycle, the level of activity at sunspot minimum, and the size of the previous cycle.

    Among the most reliable techniques are those that use the measurements of changes in the Earth's magnetic field at, and before, sunspot minimum. These changes in the Earth's magnetic field are known to be caused by solar storms but the precise connections between them and future solar activity levels is still uncertain.


    Credit: Marshall Space Flight Center

    Of these "geomagnetic precursor" techniques three stand out. The earliest is from Ohl and Ohl [Solar-Terrestrial Predictions Proceedings, Vol. II. 258 (1979)] They found that the value of the geomagnetic aa index at its minimum was related to the sunspot number during the ensuing maximum. The primary disadvantage of this technique is that the minimum in the geomagnetic aa index often occurs slightly after sunspot minimum so the prediction isn't available until the sunspot cycle has started.

    An alternative method is due to a process suggested by Joan Feynman. She separates the geomagnetic aa index into two components: one in phase with and proportional to the sunspot number, the other component is then the remaining signal. This remaining signal has, in the past, given good estimates of the sunspot numbers several years in advance. The maximum in this signal occurs near sunspot minimum and is proportional to the sunspot number during the following maximum. This method does allow for a prediction of the next sunspot maximum at the time of sunspot minimum.

    A third method is due to Richard Thompson [Solar Physics 148, 383 (1993)]. He found a relationship between the number of days during a sunspot cycle in which the geomagnetic field was "disturbed" and the amplitude of the next sunspot maximum. His method has the advantage of giving a prediction for the size of the next sunspot maximum well before sunspot minimum.

    We have suggested using the average of the predictions given by the Feynman-based method and by Thompson's method.(2). However, both of these methods were impacted by the "Halloween Events" of October/November 2003 which were not reflected in the sunspot numbers. Both methods give larger than average amplitude to Cycle 24 while its delayed start and low minimum strongly suggest a much smaller cycle.

    The smoothed aa index reached its minimum (a record low) of 8.4 in September of 2009. Using Ohl's method now indicates a maximum sunspot number of 70 ± 18 for cycle 24. We then use the shape of the sunspot cycle as described by Hathaway, Wilson, and Reichmann [Solar Physics 151, 177 (1994)] and determine a starting time and amplitude for the cycle to produce a prediction of the monthly sunspot numbers through the next cycle. We find a maximum of about 66 in the Fall of 2013.

    As the cycle progresses, the prediction process switches over to giving more weight to the fitting of the monthly values to the cycle shape function. At this phase of cycle 24 we now give 80% weight to the amplitude from curve-fitting technique of Hathaway, Wilson, and Reichmann Solar Physics 151, 177 (1994). That technique currently gives similar values to those of Ohl's method.

    Another indicator of the level of solar activity is the flux of radio emission from the Sun at a wavelength of 10.7 cm (2.8 GHz frequency). This flux has been measured daily since 1947. It is an important indicator of solar activity because it tends to follow the changes in the solar ultraviolet that influence the Earth's upper atmosphere and ionosphere.

    Many models of the upper atmosphere use the 10.7 cm flux (F10.7) as input to determine atmospheric densities and satellite drag. F10.7 has been shown to follow the sunspot number quite closely and similar prediction techniques can be used.  Current values for F10.7 can be found at: ftp://ftp.geolab.nrcan.gc.ca/data/solar_flux/daily_flux_values/fluxtable.txt.

    NOTES:

    (1) Hathaway, Wilson, and Reichmann  Solar Physics; 151, 177 (1994
    (2)  Hathaway, Wilson, and Reichmann J. Geophys. Res. 104, 22,375 (1999)

    Comments

    Is there data that takes into account the flipping of sun's poles: which one travels 1st and how long before other migrates to opposite pole?

    Hank
    Sure, every 11 years - that is considered the peak of the solar cycle.
    MikeCrow
    There is a delay between of the field reversal between the northern and southern Solar magnetic fields, I think of ~ 1 year.
    Dr. Leif Svalgaard has discussed it in the past. I couldn't find his exact comment, or the specific paper, but I do have a link to his research.

    Ah, here's one doc that discusses this.
    Never is a long time.
    Thanx Mi Cro for link
    I'm wondering since N pole and S pole don't move at same time or pace, is there pattern over our records that gives a tell on strength of 11 yr cycle