In July 1967 ESRIN and ESLAB, the two ESRO laboratories primarily concerned with basic research, held a joint symposium on Satellite and Rocket Measurements of Corpuscular Radiation from Outer Space. This was followed in September 1968 by a second symposium: Low-Frequency Waves and Irregularities in the Ionosphere; and in September 1969 by a third: Intercorrelated Satellite Observations Related to Solar Events. A fourth symposium, on upper atmospheric models and related experiments, took place in Frascati, 6-10 July 1970. The main aim of the symposium was to ~ssess current experimental work - both field and laboratory - related to mesospheric struc ture and composition, in the light of theoretical work on atmospheric models and atomic and molecular processes. To foster an interdisciplinary approach, the meeting brought together approximately 50 scientists working with different techniques but having a common interest in the interpretation of meso spheric phenomena. Recent work such as that presented at the symposium has deepened our knowledge of upper atmospheric composition, and increased our understanding of upper atmo spheric temperature and dynamics. In particular, it has shown that the concentration of minor species in the atmosphere is somewhat different than expected. Theoretical models have not yet considered many of the minor constituents and have generally not included dynamical effects. It is now time to reconsider these models and elaborate them in the light of recent knowledge.

Existing photochemical theories of stratospheric ozone are surveyed. Recent modifications to Chapman's 1930 classical model have been focused on the search for additional sinks for stratospheric ozone, while relatively little attention has been given to the uncertainties in its production rate. A critical discussion is presented on the uncertainties involved in the photo-dissociation rate of molecular oxygen which is the determining factor in the ozone production rate. (Author).

The reader may be surprised to learn that the word "aeronomy" is not found in many of the standard dictionaries of the English language (for exam ple. Webster's International dictionary). Yet the term would appear to exist, as evidenced by the affiliations of the two authors of this volume (Institut d'Aeronomie, Brussels, Belgium; Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA). Perhaps part of this obscu rity arises because aeronomy is a relatively new and evolving field of endeavor, with a history dating back no farther than about 1940. The Chambers dic tionary of science and technology provides the following definition: "aeronomy (Meteor. ). The branch of science dealing with the atmosphere of the Earth and the other planets with reference to their chemical com position, physical properties, relative motion,

The reader may be surprised to learn that the word "aeronomy" is not found in many of the standard dictionaries of the English language (for exam ple, Webster's International dictionary). Yet the term would appear to exist, as evidenced by the affiliations of the two authors of this volume (Institut d' Aeronomie Spatiale, Brussels, Belgium; Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA). Perhaps part of this obscurity arises because aeronomy is a relatively new and evolving field of endeavor, with a history dating back no farther than about 1940. The Chambers dictionary of science and technology provides the following defini tion: "aeronomy (Meteor. ). The branch of science dealing with the atmo sphere of the Earth and the other planets with reference to their chemi cal composition, physical properties, relative motion, and reactions to radiation from outer space" This seems to us an appropriate description, and it is reflected throughout the content of this volume. The study of the aeronomy of the middle atmosphere experienced rapid growth and development during the 1970's and 1980's, particularly due to con cern over the possibility of anthropogenic perturbations to the state of the middle atmosphere and its protective ozone layer. As a result, much has been learned regarding both the natural behavior of the atmosphere and the impact of man's activities upon it. In this book we shall attempt to describe the current state of the art as we see it.

"[...] an interesting and well-written overview of the current status of our knowledge of the composition of the middle atmosphere and the basic radiative, dynamical and photochemical processes which maintain it." (Bulletin American Meteorological Society)