The Spatial Coherence of African Rainfall Anomalies: Interhemispheric Teleconnections

The spatial patterns of rainfall variability over the African continent are examined using a regionally averaged data set comprising the records of 1087 stations. Typical rainfall departure patterns, or anomaly types, are derived using a linear correlation method to assess the similarity of annual departure maps for the years 1901 to 1973. For the region north of the equator, most years fall into one of six types, four of which show a strong opposition between equatorial and subtropical latitudes and two of which show departures of the same sign over the whole region. For the continent as a whole, six types are also derived. These reflect the patterns derived using northern Africa alone, with conditions in the southern subtropics resembling those in subtropical latitudes north of the equator. Continentally, two principal spatial patterns of rainfall variation are evident: anomalies of the same sign over most of Africa and anomalies of the opposite sign in equatorial and subtropical latitudes. Thus, strong interhemispheric teleconnections in rainfall are apparent. The results are discussed in the framework of common continental factors in rainfall variability and in regional climate dynamics.