Rudolf von Steiger

The Solar Wind

Shortly before the beginning of the space age, Eugene N. Parker of the University of Chicago predicted that interplanetary space would be filled with a plasma flowing rapidly outward from the Sun (Parker 1958). The likelihood that the Sun ejects charged particles that cause auroral and magnetic activity on Earth was generally accepted by that time. The observation that the plasma tails of active comets always point almost radially away from the Sun led Ludwig Biermann (1951) to postulate that the solar corpuscular radiation is continuous, rather than intermittent.It was also known that the outer atmosphere of the Sun, the solar corona, was extremely hot, with a temperature exceeding a million degrees. Sidney Chapman (1957) calculated that if the corona was in hydrostatic equilibrium, it must extend throughout the Solar System and cool off to only ~2 × 105K at the orbit of Earth. Parker (1958) put all these ideas together, explaining that the inward pressure of the interstellar medium was too weak to allow the solar atmosphere to be in hydrostatic equilibrium. He coined the phrase “solar wind” to describe the outward flowing solar Corona which supplies the pressure required to stand off the local interstellar medium, to exert the necessary force on cometary plasma tails, and to transmit solar disturbances to the geomagnetic field

O5+ IN HIGH SPEED SOLAR WIND STREAMS : SWICS/ULYSSES RESULTS

Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest in observing O5+ in situ in order to understand the relative importance of O5+ with respect to the much more abundant O6+. High speed streams are the prime candidates for the search for O5+ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present the first measurement of O5+ in the solar wind and compare these data with those of the more abundant oxygen species O6+ and O7+. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas.

Transport and Deposition

Having successfully propagated through the heliosphere and the geomagnetic field (Sects. 5.7 and 5.8), a cosmic ray enters the atmosphere. In Chap. 10, we have described how a cascade of secondary particles (protons and neutrons) then develops, which attenuates with atmospheric depth. Due to the geomagnetic shielding which excludes primary particles below the cut-off rigidity, the cascade is both depth and latitude dependent. The cascade interacts with atmospheric atoms to generate the cosmogenic radionuclides. As a result of all these processes, the production rate is proportional to the proton and neutron fluxes and therefore depends strongly on atmospheric depth, geomagnetic latitude, solar activity, and geomagnetic field intensity, as summarized by the figures in Chap. 10.

Introduction to Applications

In the two previous Parts we have seen how cosmic ray particles (protons, alpha particles, and heavier nuclei) are accelerated almost to the speed of light when a massive star nearing the end of its life explodes as a supernova. The cosmic ray particles then travel in a “random walk” through their home galaxy for millions of years before interacting with matter or escaping into inter-galactic space. For those produced in our own galaxy the average residence time is six million years. Those of them that approach planet Earth must overcome two barriers before they can enter our atmosphere.

Introduction to Cosmogenic Radionuclides

In Part 2 we have discussed the cosmic radiation, one of the links between the Earth and the cosmos. Although called “cosmic radiation” it consists of particles originating mainly from our galaxy. These play a fundamental role in the generation of the cosmogenic radionuclides that this book is all about. The six following chapters (Chaps. 10–15) in this Part describe how and where cosmogenic radionuclides are produced, how nature deposited them in archives, and how we measure them.

Bidirectional Proton Flows and Comparison of Freezing-in Temperatures in ICMEs and Magnetic Clouds

From all the transient events identified in interplanetary space by in-situ measurements, Magnetic Clouds (MCs) are among the most intriguing ones. They are a special kind of Interplanetary Coronal Mass Ejections (ICMEs), characterized by a well-defined magnetic field configuration. We use a list of 40 MCs detected by Ulysses to study bidirectional flows of protons in the

Multi-scale Physics in Coronal Heating and Solar Wind Acceleration

\sim

The Cosmic Radiation Near Earth

0.5 MeV energy range. Solar wind ions are also analysed in order to compare cloud to non-cloud ICMEs.The enhancement in freezing-in temperatures inside the clouds, obtained with data from the SWICS instrument, provides insights into processes occurring early during the ejection of the material and represents a complementary tool to differentiate cloud from non-cloud ICMEs. At higher energies, directional information for protons obtained with the EPAC instrument allows a comparison with previous results concerning bidirectional suprathermal electrons. The findings are qualitatively comparable. Apparently, the portion of bidirectional flows inside magnetic clouds is neither heavily dependent on distance from the Sun nor on parameters obtained from a flux rope model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Solar Cosmic Radiation

UVCS Observations of Temperature and Velocity Profiles in Coronal Holes.- Helios: Evolution of Distribution Functions 0.3-1 AU.- Sources of Solar Wind at Solar Minimum: Constraints from Composition Data.- SUMER Observations of Coronal-Hole Temperatures.- Recent Observations of Plasma and Alfvenic Wave Energy Injection at the Base of the Fast Solar Wind.- Solar Wind Models from the Chromosphere to 1 AU.- Semiempirical Models of the Slow and Fast Solar Wind.- Self-Consistent Models of the Solar Wind.- Alfven Waves: Coherent Phenomena in Coronal Loops and Open-Field Regions.- The Structure and Dynamics of the Corona-Heliosphere Connection.- Magnetic Reconnection in the Solar Wind.- Interchange Reconnection: Remote Sensing of Solar Signature and Role in Heliospheric Magnetic Flux Budget.- On the Role of Interchange Reconnection in the Generation of the Slow Solar Wind.- Ion Heating and Acceleration During Magnetic Reconnection Relevant to the Corona.- Power Law Distributions of Suprathermal Ions in the Quiet Solar Wind.- Three-Dimensional Simulations of Magnetic Reconnection With or Without Velocity Shears.- Emerging Parameter Space Map of Magnetic Reconnection in Collisional and Kinetic Regimes.- Magnetic Reconnection for Coronal Conditions: Reconnection Rates, Secondary Islands and Onset.- Kinetic Models for Whistler Wave Scattering of Electrons in the Solar Corona and Wind.- Solar Wind Electron Transport: Interplanetary Electric Field and Heat Conduction.- Anisotropy in Space Plasma Turbulence: Solar Wind Observations.- Scalings, Cascade and Intermittency in Solar Wind Turbulence.- Interactions of Alfven-Cyclotron Waves with Ions in the Solar Wind.- Ion Kinetics in the Solar Wind: Coupling Global Expansion to Local Microphysics.- Nonmodal Linear Theory for Space Plasmas.

Production of Cosmogenic Radionuclides in Other Environmental Systems

The half-lives of the cosmogenic radionuclides are very short compared to the age of the Earth, and none would now exist on Earth without their continuous production through the interaction of cosmic rays with the atmosphere. Seventy-five years of instrumental observations have shown that the intensity of ~3 GeV cosmic rays changes by ≥20% over time scales of ~10 years, superimposed upon longer term changes that are not well defined in the instrumental record (see Chaps. 6 and 7). The geomagnetic field has a strong screening effect upon the cosmic radiation as well and, as a consequence the production rates of the cosmogenic radionuclides near the equator are approximately 10% of those in the polar caps. This screening effect is strongly influenced by the strength and configuration of the geomagnetic field, which also changes greatly over time. Any study of the cosmogenic radionuclides, or their utilization for scientific or practical purposes therefore demands an understanding of the properties of the cosmic radiation itself and the screening imposed by the geomagnetic field.