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- Title
Enhanced Northern Hemisphere Correlation Skill of Subseasonal Predictions in the Strong Negative Phase of the Arctic Oscillation.
- Authors
Minami, Atsushi; Takaya, Yuhei
- Abstract
The Arctic Oscillation (AO) is the most dominant atmospheric variability in the Northern Hemisphere in boreal winter. Its negative phases sometimes bring extreme cold conditions over Eurasia and North America in boreal winter, impinging on various socioeconomic sectors. Thus, accurate prediction of the AO‐related conditions with a long lead time is greatly anticipated. This study investigates conditional prediction skill in the northern extratropics relative to AO phases using retrospective forecast data of multiple models provided by the Subseasonal to Seasonal Prediction Project, which is jointly conducted by the World Weather Research Programme and the World Climate Research Programme. We found that predictions starting from the strong negative AO phase tend to have enhanced prediction skill in terms of the anomaly correlation coefficient of 500‐hPa geopotential height, which measures the similarity of spatial patterns. The skill enhancement is not apparent in terms of the root mean square error score. We also discuss dynamical mechanisms behind the enhanced prediction skill. The Eliassen‐Palm flux diagnosis indicated that the strong negative AO phase induces the stronger eddy‐zonal flow feedback to sustain the anomalous zonal flow condition than the strong positive AO phase. Moreover, the anomalous zonal flow is associated with an anomalous zonally asymmetric pattern. As a result, the anomalous AO pattern is better predicted in the strong negative AO phase, contributing to the enhancement of the Northern Hemisphere correlation skill. Results highlight that dynamics inherent in the extratropical atmosphere can provide the subseasonal predictability in a certain atmospheric condition. Plain Language Summary: The Arctic Oscillation (AO) is an annular atmospheric circulation pattern and the most dominant atmospheric fluctuation in the Northern Hemisphere in boreal winter. Its negative phase, which corresponds to higher‐than‐normal surface pressure in the Arctic and lower‐than‐normal surface pressure in the midlatitudes, is associated with cold air outflows from the Arctic region that often create extreme cold conditions over Eurasia and North America in boreal winter. As such, accurate prediction of the AO‐related conditions with a long lead time is greatly anticipated. By evaluating retrospective forecast data of multiple models, we found enhanced prediction skill (high anomaly correlation coefficient scores) in predictions starting from the strong negative AO phase. Further analysis explains how atmospheric dynamics enhance the subseasonal predictability in the negative AO phase. Key Points: Subseasonal predictions starting from the strong negative AO phase tend to have high anomaly correlation skill in the Northern HemisphereEddy‐zonal flow interaction sustains the anomalous AO patterns associated with the high subseasonal predictabilityThe findings are supported by multiple model results of the S2S Project
- Subjects
NORTHERN Hemisphere; ARCTIC oscillation; SOCIOECONOMIC factors; ATMOSPHERIC circulation; LONG-range weather forecasting
- Publication
Journal of Geophysical Research. Atmospheres, 2020, Vol 125, Issue 10, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2019JD031268