100-C 25-C 50-C 75-C C+M 50-C+M C+Y 50-C+Y M+Y 50-M+Y 100-M 25-M 50-M 75-M 100-Y 25-Y 50-Y 75-Y 100-K 25-K 25-19-19 50-K50-40-40 75-K 75-64-64

CHAPTER 5

The Solar Wind

John T. Gosling

University of Colorado

Boulder, Colorado

1. Discovery 9. Termination of the Solar Wind


2. Statistical Properties in the Ecliptic Plane at 1 AU 10. Kinetic Properties of the Plasma


3. Nature of the Heliospheric Magnetic Field 11. Heavy Ion Content


4. Coronal and Solar Wind Stream Structure 12. Energetic Particles


5. The Heliospheric Current Sheet and Solar Latitude Effects 13. Waves and Turbulence


6. Evolution of Stream Structure with Heliocentric Distance 14. Conclusion


7. Coronal Mass Ejections and Transient Solar Wind Disturbances Bibliography


8. Variation with Distance from the Sun

T

he Solar Wind is aplasma, that is, an ionized gas, that
permeates interplanetary space. It exists as a conse-
quence of the supersonic expansion of the Sun’s hot outer
atmosphere, thesolar corona. The solar wind consists pri-
marily of electrons and protons, butalpha particlesand
many other ionic species are also present at low abundance
levels. At the orbit of Earth, 1 astronomical unit (AU) from
the Sun, typical solar wind densities, flow speeds, and tem-
peratures are on the order of 8 protons cm−^3 , 440 km/s,
and 1.2× 105 K, respectively; however, the solar wind is
highly variable in both space and time. A weak magnetic
field embedded within the solar wind plasma is effective
both in excluding some low-energy cosmic rays from the
solar system and in channeling energetic particles from the
Sun into theheliosphere.The solar wind plays an es-
sential role in shaping and stimulating planetary magne-
tospheres and the ionic tails of comets. [SeePlanetary
Magnetospheres.]

1. Discovery

1.1 Early Indirect Observations

In 1859, R. Carrington made one of the first white light ob-

servations of asolar flare. He noted that a major geomag-

netic storm began approximately 17 hours after the flare and

tentatively suggested that a causal relationship might ex-

ist between the solar and geomagnetic events. Subsequent

observations revealed numerous examples of associations

between solar flares and large geomagnetic storms. In the

early 1900s, F. Lindemann suggested that this could be ex-

plained if large geomagnetic storms result from an inter-

action between the geomagnetic field and plasma clouds

ejected into interplanetary space by solar activity. Early

studies of geomagnetic activity also noted that some ge-

omagnetic storms tend to recur at the∼27 day rotation pe-

riod of the Sun as observed from Earth, particularly during

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