How Has the Ferrel Cell Contributed to the Maintenance of Antarctic Sea Ice at Low Levels From 2016 to 2022?

This study investigates the specific circulation anomalies that have sustained the low Antarctic sea ice state since 2016. Firstly, we find a significant strengthening and southward shift in the Ferrel Cell (FC) during 2016-2022, resulting in a marked increase in southward transport of heat and moisture. Secondly, this enhanced FC is closely associated with a stronger mid-latitude wave pattern. This pattern is zonally asymmetric and greatly amplifies the poleward advections of heat and moisture, leading to the increased downward longwave radiation, more liquid precipitation and sea ice retreat in specific regions, including the western Pacific and Indian Ocean sectors, Ross and northern Weddell Seas. The mechanism deduced from the short-term period is further supported by the results of 40 ensemble members of simulations. The southward expansion of the FC and sea ice decline are closely linked to La Ni & ntilde;a-like conditions but may also be driven by anthropogenic global warming. Following the sudden decline in 2016, the Antarctic sea ice extent has persisted at historically low levels. In 2023, it reached unprecedented record lows. However, the specific atmospheric circulation anomalies that have sustained the Antarctic sea ice at low levels are still unknown. It is well-established that the Ferrel Cell, a mid-latitude atmospheric meridional circulation, plays a pivotal role in the energy exchange between the high- and mid-latitudes. Our findings indicate that the enhanced Ferrel Cell zonally intensified southward transport of heat and moisture over the sea ice regions, which sustains the overall low Antarctic sea ice state. Additionally, in the horizontal plane, the enhanced mid-latitude wave pattern is responsible for the regional sea ice retreat over the western Pacific sector, Ross Sea, Indian Ocean sector, and northern Weddell Sea, and is also closely associated with the enhanced Ferrel Cell. The effects of the enhanced Ferrel Cell on Antarctic sea ice decline are further supported by the results of large ensemble simulations. Therefore, this study suggests that concurrent with the southward shifting of the Ferrel Cell, the stronger warm and moist air intrusions, and the increased liquid precipitation, restrict the Antarctic sea ice expansion following its sudden decline. Since 2016, the low Antarctic sea ice extent has persisted, consistent with heat and moisture accumulation over the sea ice edges The Ferrel Cell was enhanced and shifted southward, leading to the increased southward heat/moisture advection, and liquid precipitation The effects of the enhanced Ferrel Cell on Antarctic sea ice decline are further supported by the results of large ensemble simulations