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Scherrer, P. H.

Publications and source records attributed to Scherrer, P. H..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Average photospheric poloidal and toroidal magnetic field components near solar minimum

Average (over longitude and time) photospheric magnetic field components are derived from 3-min Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe I 5250 A of about 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (about 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the northern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21. These observations are used to discuss large-scale electric currents crossing the photosphere and angular momentum loss to the solar wind.

Duvall, T. L., Jr.↗
NASA NTRS1979

Observations of solar oscillations with periods of 160 minutes

Severny et al. (1976) have reported oscillations of the sun with a period near 160 min. A description is presented of observations made at the Stanford Solar Observatory during the time from 1975 to the present which seem to support the reports by Severny et al. At Stanford the relative velocity between a central circular area of radius 0.5 solar radius on the solar disk and most of the remaining area of the solar disk is measured. A superposed epoch analysis of the observations using a period of 160 min is discussed. An apparent agreement in phase between the obtained observational data and those reported by Severny et al. tends to support the interpretation that solar oscillations are being observed.

Scherrer, P. H.↗
NASA NTRS1978

The equatorial rotation velocity of the photosphere is measured to be the same as sunspots

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.

Svalgaard, L.↗
NASA NTRS1978

The strength of the sun's polar fields

The magnetic field strength within the polar caps of the sun is an important parameter for both the solar activity cycle and for our understanding of the interplanetary magnetic field. Measurements of the line-of-sight component of the magnetic field generally yield 0.1 to 0.2 mT near times of sunspot minimum. This paper reports measurements of the polar fields made at the Stanford Solar Observatory using the Fe I line at 525.02 nm. It is found that the average flux density poleward of 55 deg latitude is about 0.6 mT peaking to more than 1 mT at the pole and decreasing to 0.2 mT at the polar cap boundary. The total open flux through either polar cap thus becomes about 3 x 10 to the 14th Wb. It is also shown that observed magnetic field strengths vary as the line-of-sight component of nearly radial fields.

Svalgaard, L.↗
NASA NTRS1978

Using dynamo theory to predict the sunspot number during solar cycle 21

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.

Schatten, K. H.↗
NASA NTRS1978

An observational search for large-scale organization of five-minute oscillations on the sun

The large-scale solar velocity field has been measured over an aperture of radius 0.8 solar radii on 121 days between April and September, 1976. Measurements are made in the line Fe I 5123.730 A, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillation with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure.

Dittmer, P. H.↗
NASA NTRS1978

A physical mechanism for the prediction of the sunspot number during solar cycle 21

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.

Schatten, K. H.↗
NASA NTRS1977

Comparison of H-alpha synoptic charts with the large-scale solar magnetic field as observed at Stanford

Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: neutral line positions inferred from H-alpha photographs (McIntosh and Nolte, 1975) and observations of the photospheric magnetic field made with low spatial resolution (three minutes) and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable.

Duvall, T. L., Jr.↗
NASA NTRS1977

The mean magnetic field of the sun - Observations at Stanford

A solar telescope has been built to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph connected to a 22.9-m vertical Littrow spectrograph. Sun-as-a-star integrated-light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean-field magnitude has been about 0.15 G, with a typical measurement error of less than 0.05 G. The mean-field polarity pattern is essentially identical to the interplanetary-magnetic-field sector structure (seen near earth with a four-day lag). The differences in the observed structures can be understood in terms of a 'warped current sheet' model.

Scherrer, P. H.↗
NASA NTRS1977

Comparison of H alpha synoptic charts with the large-scale solar magnetic field as observed at Stanford

Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: (1) neutral line positions inferred from H alpha photographs and (2) observations of the photospheric magnetic field made with low spatial resolution (3 arc min.) and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable.

Duvall, T. L., Jr.↗
NASA NTRS1977

The mean magnetic field of the sun: Observations at Stanford

A solar telescope was built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field were made daily since May 1975. The typical mean field magnitude is about 0.15 gauss with typical measurement error less than 0.05 gauss. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (seen near the earth with a 4 day lag). The differences in the observed structures can be understood in terms of a warped current sheet model.

Scherrer, P. H.↗
NASA NTRS1977

The mean magnetic field of the sun - Method of observation and relation to the interplanetary magnetic field

The mean solar magnetic field as measured in integrated light has been observed since 1968. Since 1970 it has been observed both at Hale Observatories and at the Crimean Astrophysical Observatory. The observing procedures at both observatories and their implications for mean field measurements are discussed. A comparison of the two sets of daily observations shows that similar results are obtained at both observatories. A comparison of the mean field with the interplanetary magnetic polarity shows that the IMF sector structure has the same pattern as the mean field polarity.

Scherrer, P. H.↗
NASA NTRS1976

On the reality of a sun-weather effect

It has been reported by Wilcox et al. (1973, 1974) that the solar magnetic sector structure extended away from the sun by the solar wind has an effect on the terrestrial atmospheric vorticity, the effect being a decrease in the vorticity area index with a width of about 5 days and a minimum 1 day after the sector boundary is swept past the earth by the solar wind. In the present study the vorticity area index is filtered so as to reject variations with periods less than 3 days or greater than 13 days. The 500 mb vorticity area index is used since the observations are more homogeneous. The persistence of the solar sector/atmospheric vorticity effect in the new data when the number of sector boundary passages is increased from 54 to 131 and in the independent latitude zones 35 deg N to 55 deg N and greater than 54 deg N, as well as the greater depth of the effect near sector boundary passages as compared with all other minima, suggest that the effect is real. This is further strengthened by the analysis of Hines and Halevy (1975).

Wilcox, J. M.↗
NASA NTRS1975

The sun's magnetic sector structure

The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth from 1959 to 1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south demarcation lines between regions of persistent magnetic-polarity imbalances. These regions extend up to about 35 deg in latitude on both sides of the equator. They generally do not extend into the polar caps. The polar-cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 by 10 to the 21st power Mx.

Svalgaard, L.↗
NASA NTRS1975

The sun's magnetic sector structure

The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth during 1959-1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south running demarcation lines between regions of persistent magnetic polarity imbalances. These regions extend up to about 35 deg of latitude on both sides of the equator. They generally do not extend into the polar caps. The polar cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 x 10 to the 21st power Maxwells.

Svalgaard, L.↗
NASA NTRS1975

Seasonal variation and magnitude of the solar sector structure-atmospheric vorticity effect

Evidence is reported for a seasonal variation in the effect of solar sector structure on terrestrial atmospheric vorticity. Graphs showing average response of the 50,000-Pa vorticity area index to solar magnetic sector structure during the time interval extending from 6 days before to 6 days after the time at which a sector boundary is swept past the earth indicate that a 10% drop in the average value occurs at the time of passage, but this effect is observed only during the winter months.

Wilcox, J. M.↗
NASA NTRS1974

Influence of solar magnetic sector structure on terrestrial atmospheric vorticity

The solar magnetic sector structure has a sizable and reproducible influence on tropospheric and lower stratospheric vorticity. The average vorticity during winter in the Northern Hemisphere north of 20N latitude reaches a minimum approximately one day after the passing of a sector boundary, and then increases during the following two or three days. The effect is found at all heights within the troposphere, but is not prominent in the stratosphere, except at the lower levels. No single longitudinal interval appears to dominate the effect.

Wilcox, J. M.↗