Changes in Hadley circulation: the Azores high and winter precipitation over tropical northeast Africa

We present a study of changes in winter precipitation over a region in tropical northeast Africa during 1951–2015. A persistent drying trend is present in this region in addition to interannual variability. We present evidence that the changes in precipitation are primarily influenced by a strengthening of Azores high (AH) pressure. The correlation of AH pressure to changes in precipitation in tropical northeast Africa is statistically more significant than correlations between precipitation and the Arctic Oscillation (AO), the Southern Oscillation (SO), or the North Atlantic Oscillation (NAO). It is also shown that the AH pressure in winter has steadily increased in recent decades which explains the drying trend over tropical northeast Africa over the same period. The AH represents the subsiding branch of Hadley circulation over the north Atlantic sector, i.e., increasing pressure of the AH is evidence of intensification of Hadley circulation in the north Atlantic region since the 1950s.