John M. Wilcox

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.

Methane Leaks from North American Natural Gas Systems

Methane emissions from U.S. and Canadian natural gas systems appear larger than official estimates. Natural gas (NG) is a potential “bridge fuel” during transition to a decarbonized energy system: It emits less carbon dioxide during combustion than other fossil fuels and can be used in many industries. However, because of the high global warming potential of methane (CH4, the major component of NG), climate benefits from NG use depend on system leakage rates. Some recent estimates of leakage have challenged the benefits of switching from coal to NG, a large near-term greenhouse gas (GHG) reduction opportunity (1–3). Also, global atmospheric CH4 concentrations are on the rise, with the causes still poorly understood (4).

The interplanetary magnetic field - Solar origin and terrestrial effects.

Many observations related to the large-scale structure of the interplanetary magnetic field, its solar origin and terrestrial effects are discussed. During the period observed by spacecraft the interplanetary field was dominated by a sector structure corotating with the sun in which the field is predominantly away from the sun (on the average in the Archimedes spiral direction) for several days (as observed near the earth), and then toward the sun for several days, etc. The average sector appears to be a coherent entity with internal structure such that its preceding portion is more active than its following portion. Cosmic rays corotate with the interplanetary field, and there are differential flows associated with the sector pattern. Profound effects on geomagnetic activity and the radiation belts are produced as the sector pattern rotates past the earth. The solar origin of the sector pattern is discussed. The solar source may be associated with the large-scale weak background photospheric fields observed with the solar magnetograph. It is suggested that there may be a rather continual relation between this solar structure and terrestrial responses, of which the recurring M-Region geomagnetic storms are just the most prominent example.

Influence of solar magnetic sector structure on terrestrial atmospheric vorticity

Abstract 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 2ON 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.

Long-term evolution of solar sector structure

The large-scale structure of the solar magnetic field during the past five sunspot cycles (representing by implication a much longer interval of time) has been investigated using the polarity (toward or away from the Sun) of the interplanetary magnetic field as inferred from polar geomagnetic observations. The polarity of the interplanetary magnetic field has previously been shown to be closely related to the polarity (into or out of the Sun) of the large-scale solar magnetic field. It appears that a solar structure with four sectors per rotation persisted through the past five sunspot cycles with a synodic rotation period near 27.0 days, and a small relative westward drift during the first half of each sunspot cycle and a relative eastward drift during the second half of each cycle. Superposed on this four-sector structure there is another structure with inward field polarity, a width in solar longitude of about 100° and a synodic rotation period of about 28 to 29 days. This 28.5 day structure is usually most prominent during a few years near sunspot maximum. Some preliminary comparisons of these observed solar structures with theoretical considerations are given.

The mean magnetic field of the Sun: Observations at Stanford

A solar telescope has been 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 have been made daily since May 1975. The typical mean field magnitude has been about 0.15 G with typical measurement error less than 0.05 G. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (see 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.

A model combining the polar and the sector structured solar magnetic fields

A phenomenological model of the interplay between the polar magnetic fields of the Sun and the solar sector structure is discussed. Current sheets separate regions of opposite polarity and mark the sector boundaries in the corona. The sheets are visible as helmet streamers. The solar sector boundary is tilted with respect to central meridian, and boundaries with opposite polarity change are oppositely tilted. The tilt of a given type of boundary [(+, −) or (−, +)] changes systematically during the sunspot cycle as the polarity of the polar fields reverses. Similar reversals of the position of the streamers at the limbs takes place.If we consider (a) a sunspot cycle where the northern polar field is inward (−) during the early part of the cycle and (b) a (+, −) sector boundary at central meridian then the model predicts the following pattern; a streamer at high northern latitudes should be observed over the west limb together with a corresponding southern streamer over the east limb. The current sheet runs now NW-SE. At sunspot maximum the boundary is more in the N-S direction; later when the polar fields have completed their reversal the boundary runs NE-SW and the northern streamer should be observed over the east limb and the southern streamer over the west limb.Observational evidence in support of the model is presented, especially the findings of Hansen, Sawyer and Hansen and Koomen and Howard that the K-corona is highly structured and related to the solar sector structure.

Solar activity and the weather

Abstract The attempts during the past century to establish a connection between solar activity and the weather are discussed. Some critical remarks about the quality of much of the literature in this field are given. Several recent investigations are summarized. Use of the solar-interplanetary magnetic sector structure in future investigations may add an element of cohesiveness and interaction to these investigations.

Structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

THE interplanetary magnetic field within several astronomical units of the Sun appears to have one polarity in most of the hemisphere north of the solar equatorial plane and the opposite polarity in most of the hemisphere south of the equatorial plane1–7. The two hemispheres are separated by a curved current sheet that typically crosses the solar equatorial plane in either two or four places, thus dividing the equatorial region into either two or four sectors. Near sunspot minimum, at 1 AU the curved current sheet has a spread in latitude of typically ± 15°, so that the sector boundary (the current sheet separating the two hemispheres of opposed field polarity) is almost parallel to the solar equatorial plane. In the photosphere, on the other hand, the sector boundary makes an angle of ∼ 90° with the equatorial plane8. At 1.5 R\cirċ, in 1972 and 1973, the angle between the sector boundary and the equatorial plane was ∼ 45° (ref. 9), and at 3–10 R\cirċ the angle between boundary and plane was ∼ 25° (ref. 10). A schematic diagram of this structure for the case of four sectors is shown in Fig. 1. We here propose that a connection exists between the extent of these magnetic fields and the observed variations in cosmic ray intensity at the Earth.

Solar source of the interplanetary sector structure

The interplanetary sector structure observed by the IMP-1 satellite during three solar rotations in 1963–4 is compared with the photospheric magnetic field structure observed with the solar magnetograph at Mt. Wilson Observatory. The interplanetary sector structure was most prominent on the sun in latitudes between 10 °N and 20 °N, although the average heliographic latitude of the satellite was 3 1/2 °S. A superposed-epoch analysis of the calcium plage structure obtained from the Fraunhofer Institute daily maps of the sun is used to discuss the relation between the structure of the plages and the interplanetary sector structure. A possible explanation for the observations is discussed in terms of a North-South asymmetry in the flow of the solar wind. It is suggested that these observations favor the “equinoctial” hypothesis as compared with the “axial” hypothesis for the explanation of the semi-annual maxima in geomagnetic activity.