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The present work proposes a general rule relating the polarity of broad-band (spectral range: 5250 A to 5350 A) circular polarization fields observed in sunspots to that of the corresponding magnetic fields. The rule is illustrated with observations of particular spots.
An investigation is conducted of the full tidal problem for Mercury, Venus, Earth, and Jupiter, the tide-raising planets, taking into account the complete orbital elements, including eccentricity, inclination, and their variation with time. Data for a comparison of tidal and sunspot dates are listed in a table. The investigation shows that the alignment of the tide-raising planets within 10 degrees is a common phenomenon, occurring approximately every 10.4 years. This alignment is not associated with drastic tidal effects.
Results are reported for direct measurement of intensity fluctuations and photographic subtractions of simultaneous Doppler filtergrams of H-alpha oscillations in sunspot umbrae. The observational techniques are described, and data are presented on the intensity variations, power spectra, and specific characteristics of the oscillations. Periods for the velocity oscillations are obtained by power spectrum analysis. It is found that the oscillations are apparently continuous, and that each umbra has its own characteristic period ranging from 145 to 180 plus or minus 10 sec and a duration of at least 8 cycles. A Doppler shift of 10 km/sec, an oscillating element size of 3 sec or less, and visibility to a radius vector of about 0.9 are also observed.
Kidson's relation is briefly described. It is concluded that if a relation is found between sunspots and weather, it is likely to appear in the march of high and low pressure systems around the poles.
A principal cause for the eleven-year sunspot cycle variation in the primary cosmic ray intensity observed at earth may be a variation in the solid angle of the heliosphere occupied by the extended solar polar magnetic field. Galactic cosmic rays have relatively easy access to the inner solar system through the regular extended solar polar fields, and relatively difficult access through the irregular extended solar sector structure fields.
We study the available measurements of the solar constant made at ground sites and from recent space observations to determine whether sunspots or faculae produce a detectable modulation of either the solar flux or the earth's atmospheric transmission. The data from radiometers on Mariners 6 and 7 rule out any relative change of the solar constant in space due directly to faculae or spots exceeding 0.03%. This limit is two orders of magnitude smaller than previous values obtained from ground measurements. The measurements made at mountain stations of the Smithsonian Astrophysical Observatory between 1923 and 1952 show a marginally significant increase of solar constant at the level of 0.1%, related specifically to high projected facular area. Since this increase is not seen in the space measurements, we suggest that it may reflect a change in the earth's atmospheric transmission, possibly due to a change in ozone concentration induced by variation of facular ultraviolet radiation.
On physical grounds it is suggested that the sun's polar field strength near a solar minimum is closely related to the following cycle's solar activity. Four methods of estimating the sun's polar magnetic field strength near solar minimum are employed to provide an estimate of cycle 21's yearly mean sunspot number at solar maximum of 140 plus or minus 20. This estimate is considered to be a first order attempt to predict the cycle's activity using one parameter of physical importance.
On physical grounds it is suggested that the polar field strength of the sun near a solar minimum is closely related to the solar activity of the following cycle. Four methods of estimating the polar magnetic field strength of the sun near solar minimum are employed to provide an estimate of the yearly mean sunspot number of cycle 21 at solar maximum of 140 + or - 20. This estimate may be considered a first-order attempt to predict the cycle activity using one parameter of physical importance based upon dynamo theory.
The equatorial rotation rate of the photosphere was measured at effect data. It was found that scattered light has a large influence and must be taken into account properly. When this was done it was found that the rotation rate from Doppler shifts agreed very well with the rate found for sunspots. Short-term fluctuations in rotation rate (i.e. from day to day) were less than plus or minus 15 m/s and were thus within observational errors.
Soft X-ray observations of the solar corona over the period 1970-1978 show that the number of small short-lived bipolar magnetic features (X-ray bright points) varies inversely with the sunspot index. During the entire period from 1973 to 1978 most of the magnetic flux emerging at the solar surface appeared in the form of bright points. In 1970, near the peak of solar cycle 20, the contributions from bright points and from active regions appear to be approximately equal. These observations strongly support an earlier suggestion that the solar cycle may be characterized as an oscillator in wave-number space with relatively little variation in the average total rate of flux emergence.
The mutual hydrodynamic forces between parallel cylinders in a moving fluid are illustrated through several formal examples. Parallel tubes in a uniform flow are attracted or repelled depending on whether they are side by side or one ahead of the other, respectively. A pulsating or undulating tube attracts all other neighboring tubes toward itself. These hydrodynamic effects suggest that the separate flux tubes beneath the sunspots exert significant attractive forces on each other.
A solar activity prediction technique for monthly mean sunspot numbers over a period of approximately ten years from February 1979 to January 1989 is presented. This includes the predicted maximum epoch of solar cycle 21, approximately January 1980, and the predicted minimum epoch of solar cycle 22, approximately March 1987. Additionally, the solar radio flux 10.7 centimeter smooth values are included for the same time frame using a smooth 13 month empirical relationship. The incentive for predicting solar activity values is the requirement of solar flux data as input to upper atmosphere density models utilized in mission planning satellite orbital lifetime studies.
The hydrodynamics of cylindrical buoyant bubbles (magnetic flux tubes) in an atmosphere is examined. Their dynamical stability is considered, with particular attention to the Rayleigh-Taylor and Kelvin-Helmholtz instabilities. The instabilities are sufficient to cause fragmentation in the absence of some strong stabilizing effect such as surface tension or an internal azimuthal magnetic field. The results of the stability analysis are first applied to rising gas bubbles in liquids. Then, since agreement with the experimental data is found, the results are applied to the similar problem of the rising magnetic flux in the sun. Magnetic flux tubes in a fluid velocity field are intrinsically unstable, unless twisted. With the known dynamical limits on the degree of twisting, an upper limit on the diameter of the order of a few hundred kilometers is found for the stability of individual flux tubes in the photosphere. Observations show that tubes, except when clustered to form sunspots, are generally not larger than this amount. Therefore, it is suggested that the hydrodynamic instability of larger tubes is a prime cause of their absence from the solar photosphere.
It is noted that thus far no structure has been identified immediately above the chromosphere in sunspots that is invariably present and that thus might be called the transition region and corona over the spot. However, the magnetic flux tubes emerging from spots give rise to many of the plasma filled loops that characterize the active region corona. These emit strongly from ions typical of the transition region, or the corona, but seldom both simultaneously. An overview is given of the morphology, evolution, and theory of these structures.
An exceptionally highly resolved sunspot photograph is presented which reveals the fine-scale structure of the photospheric penumbra down to 0.2 arcsec. The photograph was taken through a glass filter in a 170-A FWHM band centered on 4660 A on the 65-cm vacuum Gregorian telescope at Big Bear Solar Observatory during practically perfect seeing. The photograph reveals the penumbra to be full of extremely fine-scale fibril structures, with apparent widths near the resolution limit. The three-dimensional structure of the photospheric penumbra is seen to be similar to that of the chromospheric penumbra and superpenumbra, with dark fibrils arching above a lower brighter structure and many of the bright fibrils representing portions of wider bright structures shining through the narrow spaces between the elevated dark fibrils. Thus, in contrast to previous pictures, much of the dark component of the photospheric penumbra is not physically analogous to the intergranular dark lanes in the normal photosphere.
The detection of a new kind of sunspot-associated source in which the emission comes predominantly from a ring structure with size between that of the umbra and the penumbra is reported. The absence of emission from the center of the spot is interpreted in terms of the orientation of the magnetic field and the presence of low temperature material above the umbra.
The behavior of magnetic fluxes from active regions is investigated for times near sunspot disappearance. It is found that the magnetic fluxes decrease on or near the date the spot vanishes. This effect is investigated and it is concluded that it is actually due to changes in the field, rather than through dissipation of the active region fields. This is important in considerations of the large-scale behavior of solar magnetic fields.
The structure of the heliospheric current sheet on a spherical source surface of radius 2.35 solar radii has been computed via the use of a potential field model during the first year and a half after the last sunspot minimum. The solar polar magnetic field that is not fully observed in conventional magnetograph scans was included in the computation. The computed heliospheric current sheet had a quasi-stationary structure consisting of two northward and two southward maxima in latitude per solar rotation. The extent in latitude slowly increased from about 15 deg near the start of the interval to about 45 deg near the end. The magnetic field polarity (away from the sun or toward the sun) at the subterrestrial latitude on the source surface agreed with the interplanetary magnetic field polarity observed or inferred at the earth on 82 percent of the days. The interplanetary field structure observed at the earth at this time is finely tuned to the structure of low-latitude fields on the source surface.