A study shows that assimilating high- temporal- resolution wind profile data from the PANSY radar at Japan’s Syowa Station in Antarctica improves reanalyses and forecasts of atmospheric rivers (ARs) in the Southern Hemisphere.
The paper, “Impact of Antarctic radar on Southern Hemisphere atmospheric river reanalysis and forecast,” was published in Scientific Reports.
Observational sparsity over Antarctica and the Southern Ocean reduces forecast skill for Southern Hemisphere atmospheric circulation compared with the Northern Hemisphere. Conventional radiosondes help but are limited in frequency due to cost and logistics.
Observational sparsity over Antarctica and the Southern Ocean reduces forecast skill for Southern Hemisphere atmospheric circulation compared with the Northern Hemisphere. Conventional radiosondes help but are limited in frequency due to cost and logistics.
The study used a data assimilation system to test the impact of hourly horizontal wind profiles (roughly 1.5-20 km altitude) from the Program of the Antarctic Syowa Mesosphere- Stratosphere- Troposphere/Incoherent Scatter (PANSY) radar at Syowa Station (69°S, 39.6°E). Experiments covered periods including the 2022 Year of Polar Prediction in the Southern Hemisphere (YOPP- SH) extra radiosonde campaign.
They compared reanalyses and forecasts with vs. without the PANSY data (and relative to products like ERA5).
Main findings
- Assimilating PANSY data changes initial atmospheric conditions for forecasts, even when extra YOPP-SH radiosondes are already included. These differences persist over Antarctica and the Southern Ocean.
- The data improves the representation of the atmospheric basic state (wind speed, temperature, and geopotential height) at high latitudes.
- It enhances prediction of atmospheric circulation and integrated water vapor (and related integrated vapor transport) associated with mid- latitude ARs in the Southern Hemisphere. In related analyses, including PANSY data reduced root- mean- square errors in forecasts of AR-related fields relative to ERA5 for multiple mid- latitude cases, and increased analyzed IVT in some East Antarctic interior regions where ARs occur.
ARs are long, narrow corridors of strong moisture transport that can deliver heavy precipitation and affect weather extremes. Better initial conditions over the data-sparse polar region help downstream forecasts because errors can propagate equatorward.
The results highlight the value of continuous, high- resolution radar wind observations from Antarctica for numerical weather prediction, beyond what infrequent radiosondes alone provide. The work was supported by Japan’s National Institute of Polar Research, JSPS grants, and the Japanese Antarctic Research Expedition, with experiments run on the Earth Simulator at JAMSTEC.
For the full details, see the open- access paper on Nature’s site. Related earlier work has also shown PANSY data reducing errors in mid- latitude cyclone forecasts.
Southern Ocean weather patterns are among the most intense and continuous on Earth. This vast, nearly land- free expanse (roughly south of 30- 40°S, encircling Antarctica) features strong, persistent westerly winds, frequent extratropical cyclones, and major influences from large- scale climate modes. These patterns drive the powerful Antarctic Circumpolar Current (ACC), shape precipitation and sea ice, and play a critical role in global heat, moisture, and carbon transport.
Dominant Features
Strong westerly winds (“Roaring Forties,” “Furious Fifties,” and “Screaming Sixties”): Uninterrupted by major landmasses, these winds are the strongest mean surface winds on Earth. They drive the ACC (the world’s strongest ocean current) eastward and generate large waves and storminess.
Storm track and extratropical cyclones: A band of high storm activity lies roughly between 40°- 60°S. Cyclones form frequently due to the strong meridional temperature gradient and baroclinic instability associated with the subpolar jet. These systems bring high winds, clouds, and precipitation, and they modulate heat and moisture transport.
Circumpolar trough: A belt of low pressure surrounds Antarctica, with mean sea- level pressures often below 990 hPa. This feature shows a clear semiannual oscillation.
Precipitation patterns: Precipitation tends to increase poleward and decrease at lower latitudes in recent decades (consistent with climate change projections). Storms are producing more rain in some areas, for example, observations at Macquarie Island (in the storm track) show a ~28% rainfall increase since 1979, largely because individual storms drop more precipitation rather than because there are simply more storms.
Key Climate Modes Influencing Variability
Southern Annular Mode (SAM / Antarctic Oscillation): The leading mode of variability. In its positive phase, the westerly wind belt intensifies and contracts southward toward Antarctica (stronger high- latitude winds, often linked to reduced rainfall in parts of southern Australia and changes in Antarctic sea ice and ice- shelf melt via upwelling). In its negative phase, the belt shifts equatorward. Positive SAM has become more frequent in recent decades, partly due to ozone depletion and greenhouse- gas forcing.
El Niño- Southern Oscillation (ENSO): Influences the Southern Ocean via teleconnections (e.g., deepening or weakening of the Amundsen Sea Low). La Niña often enhances certain storm patterns and can interact with positive SAM.
Amundsen Sea Low: A persistent low-pressure feature in the South Pacific sector that strongly affects West Antarctic and Peninsula weather, sea ice, and temperatures.
Other influences include the Interdecadal Pacific Oscillation and blocking highs that can steer moisture toward Antarctica.
Atmospheric Rivers (ARs)
Narrow corridors of intense moisture transport frequently occur over the Southern Ocean (especially 40°- 60°S). They are often embedded ahead of extratropical cyclone cold fronts and can extend toward Antarctica, delivering heat, moisture, and heavy precipitation or snowfall.
ARs contribute significantly to extreme precipitation events and can influence Antarctic surface mass balance (snowfall vs. melt). Recent studies (including those using Antarctic radar data such as PANSY) show that better observations improve forecasts of these systems and related mid-latitude circulation.
AR frequency has shown poleward shifts and increases over the Southern Ocean in recent decades, modulated by both circulation changes (jet shifts) and rising atmospheric moisture.
Seasonal and Regional Aspects
Seasonality: Stronger storms and higher precipitation in winter (JJA) at mid- latitudes in many sectors; more complex patterns near Antarctica involving sea- ice interactions.
Regional differences: The Pacific, Atlantic, and Indian Ocean sectors of the Southern Ocean show longitudinal variations due to the influence of South America, Africa, Australia, and the Antarctic Peninsula. Hotspots for marine heatwaves and cyclone activity exist in areas such as the western Pacific and North Ross Sea sectors.
Sea ice interactions: Expanding/contracting Antarctic sea ice strongly modulates surface fluxes, storm tracks, and cyclone intensity. Recent years have seen record- low sea- ice extents linked to atmospheric anomalies (e.g., deep Amundsen Sea Low).
Broader Climate Role and Changes
The Southern Ocean absorbs a large fraction of anthropogenic heat (~75%) and carbon (~35- 50%). Weather patterns (especially winds and storms) drive the meridional overturning circulation (upper and lower cells), upwelling of deep water, and formation of key water masses (e.g., Antarctic Bottom Water, Intermediate Water).
Observed trends include:
- Strengthening and poleward shift of the westerlies (linked to positive SAM trends).
- Increasing storm-related rainfall and freshwater input.
- Rising marine heatwave activity in some regions.
- Complex interactions with Antarctic ice-sheet mass balance via ARs, snowfall, and warm-water upwelling.
Data sparsity remains a challenge (few islands and stations), so reanalyses, satellite data, and special observing campaigns (e.g., YOPP- SH) plus Antarctic radar observations are especially valuable for improving forecasts of these patterns and associated extremes.
In short, Southern Ocean weather is characterized by relentless westerlies, frequent intense cyclones, moisture- laden atmospheric rivers, and strong modulation by the SAM and tropical teleconnections, making it both a driver of global climate and a sensitive indicator of change.
, which boasts overwhelming scale even within Showa Air Base.
Photo: JARE65 Manami Yamaoka (August 16, 2024)
The Largest Large Atmospheric Radar in Antarctica – Observation Team Blog
Impact of Antarctic radar on Southern Hemisphere atmospheric river reanalysis and forecast
Observational sparsity over Antarctica and the Southern Ocean leads to lower forecast skill for Southern Hemisphere (SH) atmospheric circulation than in the Northern Hemisphere. Extra radiosonde observations help, but their frequency is limited by cost and logistics.
Using a data assimilation system, the authors tested the impact of hourly wind profiles from the PANSY radar (Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter radar) at Japan’s Syowa Station. Assimilating these data changes the initial atmospheric conditions for weather forecasts, even when extra radiosonde data from the 2022 Year of Polar Prediction in the Southern Hemisphere (YOPP- SH) campaign are already included. The differences persist over Antarctica and the Southern Ocean.
The high- temporal- resolution Antarctic radar data improves:
- Reproducibility of the atmospheric basic state (wind speed, temperature, and geopotential height) at high latitudes.
- Prediction of atmospheric circulation and integrated water vapor associated with atmospheric rivers (ARs) over mid- latitude regions of the SH.
Additional context from the paper
ARs are narrow, long corridors of intense water- vapor transport linked to severe weather (strong winds, heavy precipitation, flooding). They contribute substantially to extreme precipitation in parts of the SH, including New Zealand, Australia, Antarctic coastal regions, and South America, and can drive strong winds, surface melting, temperature rises, and heavy snowfall in Antarctica.
Previous work already showed benefits of PANSY wind data for mid- latitude cyclone forecasts. This study focuses on ARs during the 2022 austral winter YOPP- SH period (extra radiosondes at various SH stations).
Experiments used the ALEDAS3 ensemble data assimilation system. They compared a control reanalysis (CTL, using standard PREPBUFR observations) with one that also assimilated hourly PANSY winds (OSEP) for the period ~26 April- 5 September 2022.
Mean absolute differences in wind speed, geopotential height, and temperature (700- 200 hPa) between OSEP and CTL were notable over parts of the Southern Ocean and Antarctica. These differences could propagate and amplify downstream with the jet stream.
The authors examined AR frequency and integrated water vapor transport (IVT) reproducibility, finding impacts on both reanalysis and forecasts of mid- latitude ARs.
Funding & support: Japan Society for the Promotion of Science grants, National Institute of Polar Research (NIPR) under MEXT, and the Japanese Antarctic Research Expedition (JARE). Experiments used the Earth Simulator at JAMSTEC.
Corresponding author: Kazutoshi Sato (sato.kazutoshi@nipr.ac.jp)
Authors include Kazutoshi Sato, Jun Inoue, Akira Yamazaki, Yoshihiro Tomikawa (affiliated with the Polar Environment Data Science Center, Joint Support-Center for Data Science Research, Research Organization of Information and Systems), and Kaoru Sato.
The full PDF (accepted manuscript) is available via the Nature page. Supplementary material is also linked. Because this is still an article- in- press version, minor corrections may appear in the final published form.
Journal information: Scientific Reports (2026)
DOI: 10.1038/s41598-026-61250-x
Authors: Kazutoshi Sato,
Jun Inoue,
Akira Yamazaki,
Yoshihiro Tomikawa &
Kaoru Sato
Abstract
Observational data sparsity in Antarctica and the Southern Ocean results in lower forecast skill for atmospheric circulation over the Southern Hemisphere (SH) than the Northern Hemisphere. Additional Antarctic radiosonde observations at existing observation stations can enhance accurate forecasting of severe events over the SH; however, the number of daily radiosonde observations is limited, owing to financial and operational limitations. Using a data assimilation system, this study investigates the impact of hourly wind profiles from the PANSY radar at the Japanese Antarctic Syowa Station. Assimilation of PANSY data leads to differences in the initial atmospheric conditions for weather forecasts, even including extra radiosonde observations from the Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) campaign in 2022. These differences in initial atmospheric condition persist in Antarctica and the Southern Ocean. We show that Antarctic radar data with relatively high temporal resolution has an impact on the reproducibility of atmospheric basic state (wind speed, temperature and geopotential height) over the high latitudes and the prediction of atmospheric circulation and integrated water vapor associated with atmospheric rivers over the mid latitude in SH.
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