Predictability Associated with High-Latitude Retrograde Waves in the 1979-80 Winter Season

抄録

 Retrograde long waves in the higher latitudes of Northern Hemisphere can episodically attain large amplitudes and sustain coherent phase propagation for 2-3 weeks. The potential influence of such waves on extended-range weather forecast has been conjectured but not systematically quantified. Using a set of ensemble reforecast data, this study examines the predictability associated with an extraordinary retrograde-wave episode in the 1979-80 winter. Quantified by the anomaly correlation of 500 hPa geopotential height in the 40°N-70°N latitudinal band, increased week-2 predictability is found within the sub-period with the presence of coherent retrograde waves. Some individual forecasts made within the retrograde-wave event exhibit the behavior of “return of skills”. The results suggest a future investigation into the relation between the uptick of anomaly correlation in week-2 and detailed dynamics of the retrograde waves.