Weakening of the interannual relationship between the winter Arctic Oscillation and eastern African precipitation in the late 1970s

Abstract

In this study, we investigate the changing relationship between the boreal winter Arctic Oscillation (AO) and eastern African precipitation. The results show that the negative correlation has significantly weakened since the late 1970s. And the Arabian anticyclonic circulation changed concurrently with the AO. In the mid-high troposphere, the anomalous anticyclone centred over the Arabian Peninsula in 1980–2020 moved northeastward and weakened compared to 1950–1979. Correspondingly, the anomalous downward motion over eastern Africa significantly weakened compared with that in 1950–1979, corresponding to insignificant precipitation. A further analysis suggests that AO-related Rossby wave trains in the upper troposphere may modulate the Arabian anticyclone. From 1950 to 1979, the wave activity preferred propagating eastward from the Mediterranean to Russia along a high-latitude path. In contrast, during 1980–2020, it tended to emanate southeastward towards Saudi Arabia, with a notably stronger and more eastward extension than in the earlier period.