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Physics and chemistry in space, vol. 1, geomagnetic micropulsations
JOWUSIof Atmosphericand TerrestrialPhysiclr,1971.Vol. 33, P. 623. PergamonPrene. Printed in Northem Ireland
BOOK REVIEW
Physics and Chemistry in Space, Vol. 1, Geomagnetic Micropulsations by J. A. Jacobs. Published
by Springer-Verlag,
Berlin
(1970)
1, Professor Jacobs outlines the magnetosphere as revealed by space probes; the Earth’s approximately dipolar magnetic field permeated by charged particles and the geometry of the higher latitude field lines significantly modified by the interaction of the plasma streaming continuously from the Sun. At the boundary of and within this magnetospheric volume, geomagnetic micropulsations are generated. Their global distribution and characteristics have been observed for many decades; sometimes the waveforms reveal continuous, rather regular, oscillations within the period range from 0.1 to 600 sec. While often associated with aurora and magnetic storms, highly irregular, shorter-duration pulsations are recorded. The morphology of these variations is summarised up to about April, 1969, the review is by no means exhaustive but other review articles are referenced. Chapters 3-5 deal with various aspects of the theory of magnetohydrodynamic waves and applications to the whole range of observed geomagnetic pulsations. Poloidal and toroidal oscillations are considered as possible solutions of the general wave equation for Alfven waves under the assumption of axial symmetry; perhaps too much emphasis has been placed on models with an unrealistic plasma distribution within the magnetosphere. Recent results suggest that the magnetospheric plasma densities are compatible with standing waves in the Pc3, 4 and 5 period range. Other preferred periods may be recorded at ground observatories because of resonances in the transmission coefficient for hydromagnetic waves propagating through the lower exosphere and ionosphere. There is controversy about the degree of guidance of the longer period hydromagnetic waves in the magnetosphere; however, a correct interpretation of micropulsation periods should yield information about the solar wind velocity, the position of the boundaries of the magnetosphere and plasmasphere and the plasma ion concentration along magnetic field lines. Thus, potentially, micropulsations are a very useful ground-based probe of our space environment. The detailed understanding of all the observed micropulsation activity will depend on the solution of the asymmetric case of the coupled poloidal and toroidal modes and the development of more sophisticated models of the solar wind, the magnetosphere and the ionosphere which take into account inhomogeneous small-scale structures. In summary, this is a helpful book; for the experimentalist there is a valuable review of the various theories with which his morphological results should correlate. For the theorist, there is the pointer that the models so far considered contain many simplifying assumptions and that to explain the very complicated observed pattern of micropulsation activity more sophisticated inhomogeneous models of the magnet,osphere are needed.
IN CHAPTER
BOOK REVIEW
Physics and Chemistry in Space, Vol. 1, Geomagnetic Micropulsations by J. A. Jacobs. Published
by Springer-Verlag,
Berlin
(1970)
1, Professor Jacobs outlines the magnetosphere as revealed by space probes; the Earth’s approximately dipolar magnetic field permeated by charged particles and the geometry of the higher latitude field lines significantly modified by the interaction of the plasma streaming continuously from the Sun. At the boundary of and within this magnetospheric volume, geomagnetic micropulsations are generated. Their global distribution and characteristics have been observed for many decades; sometimes the waveforms reveal continuous, rather regular, oscillations within the period range from 0.1 to 600 sec. While often associated with aurora and magnetic storms, highly irregular, shorter-duration pulsations are recorded. The morphology of these variations is summarised up to about April, 1969, the review is by no means exhaustive but other review articles are referenced. Chapters 3-5 deal with various aspects of the theory of magnetohydrodynamic waves and applications to the whole range of observed geomagnetic pulsations. Poloidal and toroidal oscillations are considered as possible solutions of the general wave equation for Alfven waves under the assumption of axial symmetry; perhaps too much emphasis has been placed on models with an unrealistic plasma distribution within the magnetosphere. Recent results suggest that the magnetospheric plasma densities are compatible with standing waves in the Pc3, 4 and 5 period range. Other preferred periods may be recorded at ground observatories because of resonances in the transmission coefficient for hydromagnetic waves propagating through the lower exosphere and ionosphere. There is controversy about the degree of guidance of the longer period hydromagnetic waves in the magnetosphere; however, a correct interpretation of micropulsation periods should yield information about the solar wind velocity, the position of the boundaries of the magnetosphere and plasmasphere and the plasma ion concentration along magnetic field lines. Thus, potentially, micropulsations are a very useful ground-based probe of our space environment. The detailed understanding of all the observed micropulsation activity will depend on the solution of the asymmetric case of the coupled poloidal and toroidal modes and the development of more sophisticated models of the solar wind, the magnetosphere and the ionosphere which take into account inhomogeneous small-scale structures. In summary, this is a helpful book; for the experimentalist there is a valuable review of the various theories with which his morphological results should correlate. For the theorist, there is the pointer that the models so far considered contain many simplifying assumptions and that to explain the very complicated observed pattern of micropulsation activity more sophisticated inhomogeneous models of the magnet,osphere are needed.
IN CHAPTER