Amundsen Sea Low

Amundsen Sea Low
Name	Amundsen Sea Low
Type	Cyclonic low-pressure system
Location	Amundsen Sea, West Antarctica
Relevance	Atmospheric circulation, Antarctic climate, ice-sheet dynamics

Amundsen Sea Low The Amundsen Sea Low is a climatological cyclonic pressure center near the Amundsen Sea that modulates atmospheric circulation over West Antarctica and the Southern Ocean. It influences regional wind patterns, sea-ice distribution, and oceanic heat transport, thereby linking atmospheric variability to ice-sheet mass balance and Southern Ocean dynamics. Researchers across British Antarctic Survey, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, University of Washington, and Scripps Institution of Oceanography study its behavior using observations and models informed by campaigns like Operation IceBridge and datasets from ERA-Interim and ERA5.

Description and Characteristics

The feature is characterized by a persistent cyclonic circulation situated typically over the Amundsen Sea and adjacent Bellingshausen Sea, influencing wind regimes over the West Antarctic Ice Sheet and the Ross Sea. Its core manifests as a minimum in sea-level pressure embedded within the broader Southern Hemisphere circumpolar trough and interacts with the Antarctic Peninsula ridge and the Transantarctic Mountains topographic gradients. The low modulates northerly and southerly flow that affects polynyas such as the Pine Island Bay polynya and drives variations in Antarctic Bottom Water formation and Circumpolar Deep Water intrusions onto continental shelves. Synoptic expressions connect to storms tracked by networks like Polar Meteorology Group and projects including International Polar Year.

Formation and Variability

Formation arises from the interplay of large-scale planetary waves, baroclinic instability along the Southern Ocean temperature gradients, and orographic steering by features including the Antarctic Peninsula and the Ellsworth Mountains. Variability occurs on intraseasonal, interannual, and decadal timescales modulated by modes such as the El Niño–Southern Oscillation, the Southern Annular Mode, and the Pacific Decadal Oscillation. Storm-track shifts linked to Rossby wave propagation and tropical-extratropical teleconnections influence the position and strength of the low, while air–sea interactions with sea-ice concentration in regions monitored by MODIS, SMOS, and SeaWiFS contribute to feedbacks. Episodic intensifications coincide with events observed during Antarctic circumpolar current variability and Subantarctic Front meanders.

Climate Drivers and Teleconnections

The low is sensitive to forcing from tropical convective anomalies associated with El Niño, La Niña, and the Madden–Julian Oscillation, which modulate Rossby wave trains connecting the Tropical Pacific to the Antarctic sector. Extratropical drivers include shifts in the Southern Annular Mode influenced by stratospheric processes such as Antarctic ozone depletion and stratospheric sudden warming events observed in reanalyses like NCEP/NCAR. Tropical–polar links mediated by the Pacific South American pattern and interactions with the Indian Ocean Dipole alter the climatological mean and variance of the low, as detected in coupled model experiments by groups at Geophysical Fluid Dynamics Laboratory and Met Office Hadley Centre.

Impacts on Antarctic Ice and Oceanography

By steering shelf-break winds and modifying surface stress, the low enhances upwelling of warm Circumpolar Deep Water onto the continental shelves adjacent to Pine Island Glacier and Thwaites Glacier, accelerating basal melting and influencing grounding-line retreat. Changes in wind-driven sea-ice export affect stratification and basal-freshwater fluxes that govern Antarctic Bottom Water formation, with consequences for global thermohaline circulation nodes such as the Atlantic Meridional Overturning Circulation. Cryospheric responses documented by ICESat, CryoSat-2, and GRACE include mass loss episodes in the Amundsen Sea Embayment tied to persistent low phases, with implications for sea-level contributions monitored by Intergovernmental Panel on Climate Change assessments.

Observational and Modeling Studies

Observational efforts combine in situ arrays like Southern Ocean Observing System floats, ship-based hydrography from RV Nathaniel B. Palmer, and remote sensing by instruments including AVHRR and Sentinel-1. Reanalysis products such as ERA5 and JRA-55 and coupled climate models from CMIP5 and CMIP6 provide diagnostics of the low’s behavior, while regional downscaling using models like MAR and ROMS captures shelf processes. Studies harnessing data-assimilation frameworks at European Centre for Medium-Range Weather Forecasts assess predictability, and idealized experiments by researchers at Princeton University and Massachusetts Institute of Technology probe mechanistic links between tropical forcing and Antarctic responses.

Historical Trends and Future Projections

Long-term analyses reveal trends toward deepening and poleward shifts in the low during periods of strong Antarctic ozone depletion and positive Southern Annular Mode phases, with attribution studies implicating greenhouse gas forcing and stratospheric ozone changes assessed by teams at NOAA and CSIRO. Future projections from CMIP6 ensembles indicate possible continued changes in the frequency and persistence of low events under different Representative Concentration Pathway and Shared Socioeconomic Pathway scenarios, affecting projections of regional basal melt and global sea-level rise used by the IPCC AR6 community. Ongoing research priorities include improving representation in Earth System Models by groups at NOAA Geophysical Fluid Dynamics Laboratory and enhancing coupled process understanding via international collaborations like Southern Ocean Observing System and Scientific Committee on Antarctic Research.

Category:Antarctic climate