Does the lower stratosphere provide predictability for month-ahead wind electricity generation in Europe?

Wind power is playing an increasingly important role in Europe's electricity generation. Accurate forecasts of wind-power output on various spatial and temporal scales are therefore of high interest for the energy industry. However, predictability of near-surface wind on subseasonal time-scales has received relatively little attention. The stratosphere is an important source of subseasonal predictability in winter. Here, we study the implications of the lower stratospheric circulation for month-ahead wind electricity generation in Europe in winter. Using ERA-Interim reanalysis and the novel wind-power dataset Renewables.ninja, we demonstrate a strong relationship between the lower stratospheric circulation and month-ahead wind electricity generation in different parts of Europe in the period 1985-2014. This relationship exists due to episodes of troposphere-stratosphere coupling, which lead to prolonged periods of either the positive or negative phase of the North Atlantic Oscillation (NAO). Since these persistent NAO periods are associated with strong surface wind anomalies, they have an important impact on wind electricity generation, in particular in Northern Europe. The state of the lower stratospheric circulation also determines the exact latitudinal position of these prolonged NAO patterns, with contrasting implications for wind electricity generation in specific countries. Using simple statistical forecasts, we show that the observed relationship between the lower stratosphere and wind electricity generation can be used for skilful forecasts of month-ahead wind electricity generation. Particularly high forecast skill is found when the circulation in the lower stratosphere differs strongly from its climatological mean. Anomalous states of the lower stratospheric circulation therefore provide windows of subseasonal-range predictability for wind-power output in many European countries.