sunspot cycle


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Sunspot cycle: (above) annual relative sunspot numbers 1700-1992 (courtesy of the National Geophysical Data Center, Boulder, Colorado, US); (below) butterfly diagram 1880-1976 (courtesy of the Royal Greenwich Observatory)click for a larger image
Sunspot cycle: (above) annual relative sunspot numbers 1700-1992 (courtesy of the National Geophysical Data Center, Boulder, Colorado, US); (below) butterfly diagram 1880-1976 (courtesy of the Royal Greenwich Observatory)

sunspot cycle

The semiregular fluctuation of the number of sunspots over an average period of approximately 11 years – or 22 years if the respective magnetic polarities of the p - and f -spots are considered, because these reverse at sunspot minimum for the groups of the new cycle (see sunspots). The nature of the cycle is shown in the graph, where the index of sunspot activity is the relative sunspot number. It can be seen that the rise to sunspot maximum usually occupies a shorter time than the fall to minimum and that the amount of activity may vary considerably between two consecutive cycles. There is some evidence for a modulation of the amplitude of the cycle over a period of around 80 years, but more data are required before the reality of this can be established.

The phase of the sunspot cycle also determines the mean heliographic latitude of all groups. At minimum the first groups of the new cycle appear at ±30–35°. Thereafter the latitude range moves progressively toward the equator, until by the next minimum the mean latitude is around ±7°. Then, while the equatorial groups are petering out, those of the next cycle begin to appear in their characteristic higher latitudes. This latitudinal progression is known as Spörer's law . At any one time there may be a considerable spread in latitude, but groups are seldom seen farther than 35° or closer than 5° from the equator. The butterfly diagram is a graphical representation of Spörer's law obtained by plotting the mean heliographic latitude of individual groups against time (see graph). Its appearance has been likened to successive pairs of butterfly wings, hence the name.

The underlying cause of the sunspot cycle is thought to be the interplay between a large-scale relatively weak poloidal magnetic field beneath the photosphere, differential rotation, and convection. The poloidal field, which is constrained to move with the ionized solar material, becomes increasingly distorted by differential rotation until an intense toroidal field is produced. The strength of this field is further enhanced by the perturbing effect of convection, which twists the field lines into ropelike configurations that may penetrate through the surface to form sunspots. This will occur first in intermediate latitudes, where the field's rate of shearing is greatest, and thereafter in increasingly low latitudes.

The inclination to the equator of the fields of opposite polarity associated with the p - and f -spots is such that they may drift apart in both longitude and latitude, as a result of differential rotation and the cyclonic rotation of individual supergranular cells (see supergranulation). The latitudinal drift is responsible for an accumulation in the polar regions of magnetic flux of the same polarity as the f -spots in the respective hemispheres. Thus the intense (0.2–0.4 tesla) localized fields of sunspots are gradually dispersed to form weak (1–2 × 10–4 tesla) polar fields, which reverse polarity (not necessarily synchronously) around sunspot maximum. When this happens differential rotation no longer intensifies the subphotospheric toroidal field but rather weakens it and reestablishes a poloidal field of opposite direction to its predecessor.

The sunspot cycle may therefore be regarded (if this model is correct) as a relaxation process that is continually repeating itself. There is reason to believe, however, that at least some of the features of recent cycles may be transitory. In particular, a prolonged minimum, termed the Maunder minimum, from about 1645 to 1715, suggests that there is more than one circulatory mode available to the solar dynamo.

Sunspots are the most obvious but by no means the only manifestation of solar activity to undergo a cyclical change over a period of around 11 years. It is therefore proper to restrict the use of the term sunspot cycle to consideration of the fluctuation of the number of sunspots and to use the more general term solar cycle when considering the variation in the level of solar activity as a whole.

sunspot cycle

[′sən‚spät ‚sī·kəl]
(astronomy)
Variation of the size and number of sunspots in an 11-year cycle which is shared by all other forms of solar activity.
References in periodicals archive ?
In particular, they wanted to know why this last sunspot cycle was the weakest one in a hundred years (S&T: Nov.
ThinkAdvisor recently interviewed the so-called "Contrarian's Contrarian," who talked about, among other issues, the tax cut, why he expects investors to be fuming at their FAs and why the sunspot cycle (you read that correctly) is a valid predictor of market crashes.
Because the XRBG varies by more than two orders of magnitude over the course of the sunspot cycle based on the annual averages, obviously, the full-Sun X-ray sensors onboard the GOES do not see the smaller soft X-ray events (i.
This edition has a new chapter on exoplanets; new coverage of the altazimuth coordinate system; revised coverage of planet classification; expanded coverage of the satellites of the planets; and scientific updates related to physics and astronomy, including the discovery of the Higgs boson, indications of water activity on Mars, observations of fragmentation of an asteroid and rings around another one, the meeting of the Rosetta spacecraft with Comet 67P/Churyumov-Gerasimenko, the discovery of new exoplanets, the sunspot cycle, the improved parallax measurements by Gaia and the Hubble Space Telescope, and new properties of the solar wind.
The Sun is currently near the high-activity part of its 11-year sunspot cycle, so you should be able to find a sunspot or two.
The technique opens the door for near real-time mapping of the sun's roiling interior - movement that affects a wide range of events on the sun from its 22-year sunspot cycle to its frequent bursts of X-ray light called solar flares.
It's amazing to see such low activity at the peak of our sunspot cycle.
The frequency of geomagnetic storm sudden commencements, however, does not seem to follow the sunspot cycle.
gov/science-news/science-at-nasa/2013/01mar_twinpeaks/) said , "2013 is supposed to be the year of Solar Max, the peak of the 11-year sunspot cycle.
Concerns about the vulnerabilities of technical infrastructure to space weather have been growing since the sun entered the early stages of the current sunspot cycle in 2009, increasing prospects for severe solar storms," the report reads.
Scientists say the sun has been relatively quiet over the past two winters - as Irish weather-watchers know - even though it is supposed to be approaching a peak in its 11-year sunspot cycle.