To the 75th anniversary of the discovery of African Easterly Waves

This contribution will review the publications of Piersig and Regula, which both appeared in 1936 in German and which many meteorologists regard as the first descriptions of what is now well known as “African Easterly Waves (AEWs)”. Piersig investigated daily surface pressure maps, the so-called “Hoffmeyer Maps” issued by the “Deutsche Seewarte” and the Danish Meteorological Institute, over the Atlantic Ocean for the years 1881–1911. He also used ship weather records and data from two stations on the Cape Verde Islands. His “Type 4 cyclonic disturbances” occur south of the trade wind zone off the West Coast of Africa and are most likely represent the passage of an AEW. Piersig describes typical tracks of “Type 4 cyclonic disturbances” and a case in late August/early September 1911. Regula identified variations in mean sea-level pressure (MSLP) at a period of four days at West African coastal stations reaching from Monrovia (6°N) to Rio de Oro (24°N) between July and October 1934. Piersig observed the following characteristics which are consistent with our present understanding of AEWs: (a) The MSLP fluctuations are most pronounced at the northern stations, but occur earlier in the south; and (b) an enhanced frequency of thunderstorms with gales when the MSLP increases. While Piersig's work has been translated into English and published in the Bulletin of the American Meteorological Society in 1944, the work of Regula is less well recognized in the anglophone literature. The presentation will also touch upon other early work on AEWs by, for example, Hubert and Riehl, as well as to what extent this early work was recognized in the seminal papers on AEWs by Carlson (1969a,b), Burpee (1972; 1974), and Reed et al. (1977).