Kenneth H. Schatten

A model of interplanetary and coronal magnetic fields

A model of the large-scale magnetic field structure above the photosphere uses a Greens function solution to Maxwells equations. Sources for the magnetic field are related to the observed photospheric field and to the field computed at a ‘source’ surface about 0.6 R⊙ above the photosphere. The large-scale interplanetary magnetic field sector pattern is related to the field pattern at this ‘source’ surface. The model generates magnetic field patterns on the ‘source’ surface that compare well with interplanetary observations. Comparisons are shown with observations of the interplanetary magnetic field obtained by the IMP-3 satellite.

Group Sunspot Numbers: A New Solar Activity Reconstruction

In this paper, we construct a time series known as the Group Sunspot Number. The Group Sunspot Number is designed to be more internally self-consistent (i.e., less dependent upon seeing the tiniest spots) and less noisy than the Wolf Sunspot Number. It uses the number of sunspot groups observed, rather than groups and individual sunspots. Daily, monthly, and yearly means are derived from 1610 to the present. The Group Sunspot Numbers use 65941 observations from 117 observers active before 1874 that were not used by Wolf in constructing his time series. Hence, we have calculated daily values of solar activity on 111358 days for 1610–1995, compared to 66168 days for the Wolf Sunspot Numbers. The Group Sunspot Numbers also have estimates of their random and systematic errors tabulated. The generation and preliminary analysis of the Group Sunspot Numbers allow us to make several conclusions: (1) Solar activity before 1882 is lower than generally assumed and consequently solar activity in the last few decades is higher than it has been for several centuries. (2) There was a solar activity peak in 1801 and not 1805 so there is no long anomalous cycle of 17 years as reported in the Wolf Sunspot Numbers. The longest cycle now lasts no more than 15 years. (3) The Wolf Sunspot Numbers have many inhomogeneities in them arising from observer noise and this noise affects the daily, monthly, and yearly means. The Group Sunspot Numbers also have observer noise, but it is considerably less than the noise in the Wolf Sunspot Numbers. The Group Sunspot Number is designed to be similar to the Wolf Sunspot Number, but, even if both indices had perfect inputs, some differences are expected, primarily in the daily values.

A discussion of plausible solar irradiance variations, 1700‐1992

From satellite observations the solar total irradiance is known to vary. Sunspot blocking, facular emission, and network emission are three identified causes for the variations. In this paper we examine several different solar indices measured over the past century that are potential proxy measures for the Suns irradiance. These indices are (1) the equatorial solar rotation rate, (2) the sunspot structure, the decay rate of individual sunspots, and the number of sunspots without umbrae, and (3) the length and decay rate of the sunspot cycle. Each index can be used to develop a model for the Suns total irradiance as seen at the Earth. Three solar indices allow the irradiance to be modeled back to the mid-1700s. The indices are (1) the length of the solar cycle, (2) the normalized decay rate of the solar cycle, and (3) the mean level of solar activity. All the indices are well correlated, and one possible explanation for their nearly simultaneous variations is changes in the Suns convective energy transport. Although changes in the Suns convective energy transport are outside the realm of normal stellar structure theory (e.g., mixing length theory), one can imagine variations arising from even the simplest view of sunspots as vertical tubes of magnetic flux, which would serve as rigid pillars affecting the energy flow patterns by ensuring larger-scale eddies. A composite solar irradiance model, based upon these proxies, is compared to the northern hemisphere temperature departures for 1700-1992. Approximately 71% of the decadal variance in the last century can be modeled with these solar indices, although this analysis does not include anthropogenic or other variations which would affect the results. Over the entire three centuries, ∼50% of the variance is modeled. Both this analysis and previous similar analyses have correlations of model solar irradiances and measured Earth surface temperatures that are significant at better than the 95% confidence level. To understand our present climate variations, we must place the anthropogenic variations in the context of natural variability from solar, volcanic, oceanic, and other sources.

Influence of a solar active region on the interplanetary magnetic field

The interplanetary magnetic field has been mapped between 0.4 and 1.2 AU in the ecliptic plane, extrapolating from satellite measurements at 1 AU. The structure within sectors and the evolution of sectors are discussed. The development of a solar active region appears to produce magnetic loops in the interplanetary medium that result in the formation of a new sector.

Photospheric Magnetic Field Rotation: Rigid and Differential

An autocorrelation of the direction of the large-scale photospheric magnetic field observed during 1959–1967 has yielded evidence that the field structure at some heliographic latitudes can display both differential rotation and rigid rotation properties.

Heliographic latitude dependence of the Sun's irradiance

It has recently been reported that the total radiative emission variations from solar type stars exceeds the currently observed solar constant variations (from spacecraft over the last decade) by a factor near 4. Aside from other remote alternatives, this suggests three clear possibilities: (1) the Sun may undergo irradiance variations several times larger than any we have seen; (2) our Sun is highly unusual with regard to its radiative output; or (3) our terrestrial position in the heliosphere provides a special vantage point which reduces the observed solar irradiance variations. We investigate the last possibility by considering the influence of observer latitude upon calculated irradiance variations using a simple model for emission from solar contrast features. We consider modeled sunspots, faculae, and network structures. As the latitude angle of the observer rises relative to the heliographic equator, sunspot deficit contributions diminish and facular plus network contributions escalate. We find that the observing latitude can influence the irradiance variations by a factor near 6. When we integrate the irradiance variations, over the celestial sphere, they average to 3 times the terrestrial effect, suggesting that the solar cycle luminosity variations are proportionally, 3 times larger than the solar constant variations. Thus we suggest the Suns luminosity output varies even more strongly with the solar cycle than is apparent in the solar constant variations. The influence of the observer viewing angle relative to stellar spin axis, studied here, may be possible to investigate with a thorough statistical examination of other solar type stars. Additionally, the rotational modulation due to active regions (as a function of observer viewing angle) may also be a valuable area for future investigation.

A hillock and cloud model for faculae

A hillock model is used here to explain facular contrasts, allowing faculae to emit more energy than the surrounding unmagnetized photosphere. For downflows, horizontal motions converge near the photosphere and many fibril flux tubes are drawn together to form a large dark area, the sunspot. For upflows, the motions diverge near the photosphere and fibril flux tubes are dispersed over a larger area associated with faculae. The upflows transport material and energy, resulting in hotter than normal temperatures, which in turn cause the gas to expand compared with its surroundings. Buoyancy thus causes a network of patchy hillocks, clouds, or geysers to form which allows the sun to reradiate the energy deficit associated with sunspots by locally increasing the effective surface area of the sun beyond that of a sphere. The consequences of this model for the physical form of the facular manifestation, the appearance of faculae from earth, and the energy balance in active regions are addressed. 34 references.

New information on solar activity, 1779-1818, from Sir William Herschel's unpublished notebooks

Herschels observations are analyzed in order to determine the level of solar activity for solar cycle 5. It is concluded that solar cycle 5 may have peaked as early as 1801 based upon the average number of groups with a probable secondary maximum in 1804. Depending on the technique adopted, the peak for solar cycle 5 occurred sometime between 1801 and 1804, rather than 1805.2, as commonly assumed. Instead of a solar cycle of 17 yrs, a cycle length of 14 yrs is found. It is also found that the peak yearly mean sunspot number is only about 38 rather than 45, as deduced by Wolf (1855). A technique for making early solar observations homogeneous with modern sunspot observations is proposed.

LONGITUDE DISTRIBUTION OF PROTON FLARES AS A FUNCTION OF RECURRENCE PERIOD.

Abstract : The longitude distribution of the solar flares that produced high-energy protons detected at the earth during the past 11-year sunspot cycle is examined. The synodic rotation period is not confined to be the Carrington period (27.2753 days) which corresponds to the use of heliographic longitude, but instead a range of rotation periods from 25 to 34 days is examined in increments of 0.01 days. It is concluded that the apparent tendency of these proton flares to cluster within one hemisphere of heliographic longitude is not statistically significant. (Author)

PERCOLATION AND THE SOLAR DYNAMO

The origin of magnetic field sources in the Sun’s dynamo is central to this paper. The Babcock-Leighton dynamo was originally envisaged as a shallow dynamo. The source of the Sun’s magnetism is now generally thought to reside near the base of the convection zone and that these fields rise by buoyancy to initiate sunspots. We reconsider this aspect of the solar dynamo. We do this by considering two surface effects as an alternative to the deep origin of the Sun’s magnetism. They are (1) small-scale convective overturning forming the magnetic carpet of ephemeral regions, and (2) percolation, a process wherein the small structures combine to form larger entities. We discuss these effects, and we develop a numerical percolation model and a set of simplified Leighton-type dynamo equations. The numerical percolation model, initiated with two separate random distributions of unipolar fields, does simulate fields clumping together into larger sunspot-like structures, but does not yet display the bipolar nature of actual sunspot structures. We provide a set of simplified global dynamo equations illustrating the temporal behavior of the current percolation model. With the current model being predominantly illustrative, it is envisaged that more realistic shallow solar dynamo models will be forthcoming. We end by providing three types of observations that may distinguish the percolation model from the deep-seated field origin dynamo models. They are (1) the temporal development of activity centers, (2) the magnetic flux distribution within groups, and (3) velocity flow patterns, near and within active regions. In addition, our modeling suggests that a long-term accounting of the amount of flux in ephemeral regions may lead to long-timescale predictions of solar activity.