The articles in this volume provide a detailed review of all aspects of the main magnetic field of the Earth produced within the Earth's core: its past history, its long and short term changes, the way it is generated. The book contains the combined knowledge of geomagnetism coming from paleomagnetic and archeomagnetic data, centuries of terrestrial observations and from the past few decades of intensive space observations. There is considerable emphasis on the phenomenology and the physical processes of the evolution of the geomagnetic field on different timescales. The book reports fully on our understanding of the present state of the magnetic field and its expected evolution in the future.

A Corotating Interaction Region (CIR) is the result of the interaction of fast solar wind with slower solar wind ahead. CIRs have a very large three-dimensional ex tent and are the dominant large-scale structure in the heliosphere on the declining and minimum phase of the solar activity cycle. Until recently, however, CIRs could only be observed close to the ecliptic plane, and their three-dimensional structure was therefore not obvious to observers and theoreticians alike. Ulysses was the first spacecraft allowing direct exploration of the third dimen sion of the heliosphere. Since 1992, when it has entered a polar orbit that takes it 0 up to 80 latitude, the spacecraft's performance has been flawless and the mission has provided excellent data from a superbly matched set of instruments. Perhaps the most exciting observation during Ulysses' first passage towards the south pole of the Sun was a strong and long lasting CIR whose energetic particle effects were observed up to unexpectedly high latitudes. These observations, documented in a number of publications, stimulated considerable new theoretical work.

Starting in 1995 numerical modeling of the Earth's dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).

Andrew F. Nagy Originally published in the journal Space Science Reviews, Volume 139, Nos 1-4. DOI: 10. 1007/s11214-008-9353-0 (c) Springer Science+Business Media B. V. 2008 Keywords Aeronomy The term "aeronomy" has been used widely for many decades, but its origin has mostly been lost over the years. It was introduced by Sydney Chapman in a Letter to the Editor, entitled "Some Thoughts on Nomenclature," in Nature in 1946 (Chapman 1946). In that letter he suggested that aeronomy should replace meteorology, writing that the word "meteor is now irrelevant and misleading." This proposal was apparently not received with much support so in a short note in Weather in 1953 Chapman (1953)wrote: "If, despite its obvious convenience of brevity in itself and its derivatives, it does not commend itself to aeronomers, I think there is a case for modifying my proposal so that instead of the word being used to signify the study of the atmosphere in general, it should be adopted with the restricted sense of the science of the upper atmosphere, for which there is no convenient short word. " In a chapter, he wrote in a 1960 book (Chapman 1960), he give his nal and de nitive de nition, by stating that "Aeronomy is the science of the upper region of the atmosphere, where dissociation and ionization are important." The Workshop on "Comparative Aeronomy" was held at ISSI during the week of June 25-29, 2007.

The articles in this volume cover, for the first time, all aspects of planetary magnetism, from the observations made by space missions to their interpretation in terms of the properties of all the planets in the solar system. Studies of dynamo-generated magnetic fields in Mercury, the Earth, the giant planets, as well as in Ganymede, one of Jupiter's moons, are presented. Crustal magnetic field in Mars, the Mon and the Earth are described as well as magnetic fields induced in the solar system bodies. There are several articles dealing with dynamo theory and modelling and applications to the different planets.

Understanding how the Sun changes though its 11-year sunspot cycle and how these changes affect the vast space around the Sun a" the heliosphere a" has been one of the principal objectives of space research since the advent of the space age. This book presents the evolution of the heliosphere through an entire solar activity cycle. The last solar cycle (cycle 23) has been the best observed from both the Earth and from a fleet of spacecraft. Of these, the joint ESA-NASA Ulysses probe has provided continuous observations of the state of the heliosphere since 1990 from a unique vantage point, that of a nearly polar orbit around the Sun. Ulyssesa (TM) results affect our understanding of the heliosphere from the interior of the Sun to the interstellar medium - beyond the outer boundary of the heliosphere. Written by scientists closely associated with the Ulysses mission, the book describes and explains the many different aspects of changes in the heliosphere in response to solar activity. In particular, the authors describe the rise in solar activity from the last minimum in solar activity in 1996 to its maximum in 2000 and the subsequent decline in activity.

This fascinating book reviews the progress made in Mercury studies since the flybys by Mariner 10 in 1974-75. Thus far, it is the only book on Mercury which balances a wide range of Earth-based observations, made under difficult conditions, with the only available space-based data. The text is based on continued research using the Mariner 10 archive, on observations from Earth, and on increasingly realistic models of this mysterious planet 's interior evolution.

The articles in this volume provide a detailed review of all aspects of the main magnetic field of the Earth produced within the Earth's core: its past history, its long and short term changes, the way it is generated. The book contains the combined knowledge of geomagnetism coming from paleomagnetic and archeomagnetic data, centuries of terrestrial observations and from the past few decades of intensive space observations. There is considerable emphasis on the phenomenology and the physical processes of the evolution of the geomagnetic field on different timescales. The book reports fully on our understanding of the present state of the magnetic field and its expected evolution in the future.

The articles in this volume cover, for the first time, all aspects of planetary magnetism, from the observations made by space missions to their interpretation in terms of the properties of all the planets in the solar system. Studies of dynamo-generated magnetic fields in Mercury, the Earth, the giant planets, as well as in Ganymede, one of Jupiter s moons, are presented. Crustal magnetic field in Mars, the Mon and the Earth are described as well as magnetic fields induced in the solar system bodies. There are several articles dealing with dynamo theory and modelling and applications to the different planets."

Starting in 1995 numerical modeling of the Earth's dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).

Andrew F. Nagy Originally published in the journal Space Science Reviews, Volume 139, Nos 1-4. DOI: 10. 1007/s11214-008-9353-0 (c) Springer Science+Business Media B. V. 2008 Keywords Aeronomy The term "aeronomy" has been used widely for many decades, but its origin has mostly been lost over the years. It was introduced by Sydney Chapman in a Letter to the Editor, entitled "Some Thoughts on Nomenclature," in Nature in 1946 (Chapman 1946). In that letter he suggested that aeronomy should replace meteorology, writing that the word "meteor is now irrelevant and misleading." This proposal was apparently not received with much support so in a short note in Weather in 1953 Chapman (1953)wrote: "If, despite its obvious convenience of brevity in itself and its derivatives, it does not commend itself to aeronomers, I think there is a case for modifying my proposal so that instead of the word being used to signify the study of the atmosphere in general, it should be adopted with the restricted sense of the science of the upper atmosphere, for which there is no convenient short word. " In a chapter, he wrote in a 1960 book (Chapman 1960), he give his nal and de nitive de nition, by stating that "Aeronomy is the science of the upper region of the atmosphere, where dissociation and ionization are important." The Workshop on "Comparative Aeronomy" was held at ISSI during the week of June 25-29, 2007.

Understanding how the Sun changes though its 11-year sunspot cycle and how these changes affect the vast space around the Sun the heliosphere has been one of the principal objectives of space research since the advent of the space age. This book presents the evolution of the heliosphere through an entire solar activity cycle. The last solar cycle (cycle 23) has been the best observed from both the Earth and from a fleet of spacecraft. Of these, the joint ESA-NASA Ulysses probe has provided continuous observations of the state of the heliosphere since 1990 from a unique vantage point, that of a nearly polar orbit around the Sun. Ulysses results affect our understanding of the heliosphere from the interior of the Sun to the interstellar medium - beyond the outer boundary of the heliosphere. Written by scientists closely associated with the Ulysses mission, the book describes and explains the many different aspects of changes in the heliosphere in response to solar activity. In particular, the authors describe the rise in solar activity from the last minimum in solar activity in 1996 to its maximum in 2000 and the subsequent decline in activity."

This fascinating book reviews the progress made in Mercury studies since the flybys by Mariner 10 in 1974-75. Thus far, it is the only book on Mercury which balances a wide range of Earth-based observations, made under difficult conditions, with the only available space-based data. The text is based on continued research using the Mariner 10 archive, on observations from Earth, and on increasingly realistic models of this mysterious planet s interior evolution."