Is Enhanced Predictability of the Amundsen Sea Low in Subseasonal to Seasonal Hindcasts Linked to Stratosphere‐Troposphere Coupling?

The Amundsen Sea low (ASL) is one of the key components of the Antarctic surface climate. Here, we assess the subseasonal to seasonal (S2S) predictive skill of the ASL in two state‐of‐the‐art forecasting systems based on the anomaly correlation coefficient (ACC). It is found that the ASL predictability during austral spring is higher than in the other seasons with lead times ranging from 1 to 4 weeks. The spring ASL predictability has an ACC of about 0.6 with lead times of 1–2 weeks and about 0.44 with lead times of 3–4 weeks. The enhanced ASL predictability during austral spring is mainly due to the strengthening of stratosphere‐troposphere coupling, coincident with a weakened stratospheric polar night jet and increased wave‐mean flow interactions in the stratosphere. This study demonstrates that the stratosphere‐troposphere coupling provides an important source of predictability for the Antarctic surface weather and climate on S2S timescale. Plain Language Summary The Amundsen Sea low (ASL) is a persistent low‐pressure system located in the Southern Ocean between the Antarctic Peninsula and the Ross Sea. The presence of the ASL strongly modifies local weather systems (e.g., storms and rainfall), as well as Antarctic sea ice. As shipping activities are increasing over the Antarctic Ocean, the predictability of the ASL is becoming increasingly important. This study assesses the ASL predictability in two state‐of‐the‐art forecasting systems and identifies a significant enhancement of subseasonal forecast skill during austral spring. Further analysis reveals that the enhancement of the ASL predictability during austral spring is related to the timing of generally increased stratosphere‐troposphere coupling, suggesting that the atmospheric subseasonal predictability may be significantly improved in forecasting systems that capture the stratosphere‐troposphere coupling well. Key Points The Amundsen Sea low (ASL) predictability in the forecasting systems has a seasonal dependency with high skill only during austral spring The skillful ASL predictions during austral spring are found to be coincident with the timing of increased stratosphere‐troposphere coupling The atmospheric subseasonal predictability may be significantly improved in forecasting systems that capture stratosphere‐troposphere coupling well