PAGEOPH, stratosphere, these differences provide us with new evidence, interpretation of which can materially help to advance our understanding of stratospheric dynamics in general. It is now weil established that smaller-scale motions-in particular gravity waves and turbulence-are of fundamental importance in the general circulation of the mesosphere; they seem to be similarly, if less spectacularly, significant in the troposphere, and probably also in the stratosphere. Our understanding of these motions, their effects on the mean circulation and their mutual interactions is progressing rapidly, as is weil illustrated by the papers in this issue; there are reports of observational studies, especially with new instruments such as the Japanese MV radar, reviews of the state of theory, a laboratory study and an analysis of gravity waves and their effects in the high resolution "SKYHI" general circulation model. There are good reasons to suspect that gravity waves may be of crucial significance in making the stratospheric circulation the way it is (modeling experience being one suggestive piece of evidence for this). Direct observational proof has thus far been prevented by the difficulty of making observations of such scales of motion in this region; in one study reported here, falling sphere observations are used to obtain information on the structure and intensity of waves in the upper stratosphere.

This book is a multi-author treatise on the most outstanding research problems in the field of the aeronomy of the Earth’s atmosphere and ionosphere, encompassing the science covered by Division II of the International Association of Geomagnetism and Aeronomy (IAGA). It contains several review articles and detailed papers by leading scientists in the field. The book is organized in five parts: 1) Mesosphere-Lower Thermosphere Dynamics and Chemistry; 2) Vertical Coupling by Upward Propagating Waves; 3) Ionospheric Electrodynamics and Structuring; 4) Thermosphere- Ionosphere Coupling, Dynamics and Trends and 5) Ionosphere-Thermosphere Disturbances and Modeling. The book consolidates the progress achieved in the field in recent years and it serves as a useful reference for graduate students as well as experienced researchers.

Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 87. This volume provides a review of progress made in recent years in experimental and theoretical investigation of the upper mesosphere and lower thermosphere and coupling between these regions and the ionosphere. Detailed study of the mesosphere/lower thermosphere/ionosphere (MLTI) region has historically been difficult because of its relative inaccessibility to direct measurement techniques and the complex and highly coupled processes which occur there. Although we have still not successfully unraveled all these complex interactions, we have made significant recent progress toward a fuller understanding of the basic state of the MLTI and of the dominant wave and coupling processes. This monograph includes a set of tutorial papers, which review our current understanding of aspects of the MLTI. These tutorials are interspersed with a selection of papers describing research progress on various topics of current interest in this region. The book should therefore be useful both to the newcomer, as an introduction to this field of research, and to the more experienced researcher, providing an overview of research in progress as well as a convenient reference collection of papers describing our current understanding.

A comprehensive overview of the structure and variability of the upper atmosphere Earth's upper atmosphere is an open system that is strongly influenced by energy and momentum inputs from both above and below. New observation and modeing techniques have provided insights into dynamics, energetics, and chemical processes in the upper atmosphere. Upper Atmosphere Dynamics and Energetics presents an overview of key research advances in upper atmospheric physics, and measurement and modeling techniques, along with remaining challenges for understanding the state and variability of the upper atmospheric system. Volume highlights include: Insights into the interconnections between different areas of upper atmospheric science Appreciation of the dynamics and complexity of the global upper atmospheric system Techniques for observing and measuring the upper atmosphere Responses of the upper atmosphere to external drivers The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Find out more about the Space Physics and Aeronomy collection in this Q&A with the Editors in Chief