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Sub-seasonal Forecast Skill for Weekly Mean Atmospheric Variability over the Northern Hemisphere in Winter and its Relationship to Mid-Latitude Teleconnections
  • Akio Yamagami,
  • Mio Matsueda
Akio Yamagami
University of Tsukuba

Corresponding Author:yamagami@ccs.tsukuba.ac.jp

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Mio Matsueda
University of Tsukuba & University of Oxford
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This study assesses the sub-seasonal predictability of the weekly mean geopotential height anomaly at 500 hPa and its relationship to teleconnections over the Northern Hemisphere in winter. The skill over the North Pacific, Canada, and Greenland is higher than over other areas for week-3 and -4 forecasts. These peaks correspond to the centers of action for the Pacific–North American (PNA) pattern and the North Atlantic Oscillation (NAO). PNA (NAO phase) predictions are better for El Niño years at lead times of 4 weeks (2–4 weeks). The effects of La Niña forcing on PNA and NAO forecasts are small compared with the El Niño forcing. Numerical models tend to predict a negative PNA at lead times of 3–4 weeks in La Niña years. The improvement in the mid-latitude upper-level jet rather than in the atmospheric response to ENSO forcing in the tropics is important for better S2S prediction.