Foreword

The papers in this issue are based upon some of the contributions presented at the Third International Symposium on Equatorial Aeronomy held at the Physical Research Laboratories, Ahmedabad, India, February 3‐10, 1969. Previous meetings of the Symposia had been held in Huaychulo, Peru, in 1962, and in Sao José dos Campos, Brazil, in 1965. The earlier meetings had started cooperative work among workers in equatorial regions, initiating a breakdown of the tendency for the worker in equatorial regions to feel himself an ‘out‐station’ from one of the metropolitan countries. The conferences had also served the purpose of bringing some degree of unification among the areas of research that had tended to be pursued in isolated channels. Aeronomy is taken to include all studies of the earth's atmosphere above 60 km. Equatorial aeronomy restricts the interest to the vicinity of the equator and to effects that originate at the equator.