This paper contains the results of a year's study of fog and haze, both their present synoptic treatment and the more recent literature dealing with them at some of the principal European forecast and aviation centers. The greater part of the investigation was made at the Geophysical Institute of Bergen, Norway, with shorter stays at Lindenburg Aeronautical Observatory and Tempelhof Field near Berlin, at the meteorological office and Le Bourget, Paris, and at the meteorological office and Croyden, London.

Grateful acknowledgments are due to the officials of and others connected with those institutions for courtesies shown during this investigation.

Part I contains a brief summary of the present state of our knowledge of nuclei of condensation, paying special attention to Aitken's and Köhler's investigations of hygroscopic nuclei, and the general evidence favoring the theory that condensation begins on hygroscopic nuclei rather than on ions or neutral dust particles.

Part II contains a general classification of the kinds of fog, followed by a consideration of the causes, characteristics, and distribution of each type. This whole development is carried out in terms of the Bergen methods of air mass analysis, because these are the only methods of synoptic treatment which stress the fine observational distinctions necessary for the consideration of a meteorological element as sensitive as fog.

Part III contains a statement of the fundamental principles to be followed in fog forecasting, again in terms of air mass properties, and a brief consideration of the application of these general principles to each specific type of fog.

Part IV contains some general elementary considerations of relations between fog frequencies and type of exposure which should be noted in choosing an aerodrome site.

Abbreviations used are as follows:

  • Rw

    relative humidity with respect to water.

  • Re

    relative humidity with respect to ice.

  • T. A.

    tropical air.

  • P. A.

    polar air.

  • W. A.

    warm air.

  • C. P. A.

    continental polar air.

  • M. P. A.

    maritime polar air.

  • Trans. A.

    transitional air.

  • C. Trans. A.

    continental transitional air.

  • M. Trans. A.

    maritime transitional air.

  • Ta

    temperature of air just above ground surface.

  • Ts

    temperature of ground (or Water) surface