From the single question, “What is the physical origin of the biennial oscillation (the biennial change in wind direction from westerly to easterly) in the tropical stratosphere?” grew this study, the most extensive ever undertaken of the tropical atmosphere on a general circulation scale. It is based mainly on a worldwide sample of free air balloon data collected from the period 1957-1964, as well as classical surface observations. As Professor Newell explains in the preface, “We aimed for a relatively long period of record to ensure sampling several cycles of the biennial oscillation, and we tried to include all available data for the region 40 degrees N to 40 degrees S. It soon became clear, as we processed the data, that other items of interest could be due to the Bali volcanic eruption of March 1963, the basic climatology of the tropics in terms of vertical motion and rainfall and their year-to-year changes, the genesis of hurricanes, interhemispheric interactions, the detailed time evolution of the Hadley cell circulation... and many other items all proved of interest.”
The first part of this study, which will shortly include a second volume, contains chapters on the sources, processing, and analysis of the data; mean temperature and wind fields; the angular momentum budget and the maintenance of the zonal wind; and seasonal variation of humidity parameters.
Volume 2 will continue with chapters on radiative heating; the heat budget; atmospheric energy balance; cloudiness, precipitation, and vertical motion; annual, semiannual, and biennial oscillations and long-term changes, including those brought about by volcanic effects; and large-scale wave disturbances in the tropical stratosphere. Throughout both volumes a set of over 250 climatological maps forms the basic presentation.