This text focuses on the physics and chemistry of the Earth's upper atmosphere, bounded at the bottom by the pressure level at which most (though not all) of the incoming ionizing radiation has been absorbed, and bounded at the top by the level at which escape of the neutral gas becomes important. The region defined by these boundaries contains a partially ionized gas. The principal ionization sources are solar ultraviolet radiation and auroral energetic particles. Thus, an ionosphere is embedded in the upper atmosphere.

The plan is to identify the multitude of processes that operate in the upper atmosphere and to relate observed input and output parameters by detailed physical and mathematical descriptions of the governing processes. The properties and behaviour of the atmosphere are a consequence of the interaction of processes that span a wide range of commonly identified disciplines; radiation physics and chemistry, transport phenomena, gas phase chemistry, fluid dynamics, optics and spectroscopy, and others. Basic disciplines are drawn upon in attempting to understand the upper atmosphere. It is hoped that this book will bridge the gap between those texts read by students taking courses in the standard disciplines of physics and the research literature in upper atmosphere physics and chemistry. Research papers all too often assume that the reader already has the background required to appreciate the new development reported in the article.