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1. The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

   https://doi.org/10.1175/BAMS-D-19-0255.1  

   Bromwich, David H.; Werner, Kirstin; Casati, Barbara; Powers, Jordan G.; Gorodetskaya, Irina V.; Massonnet, François; Vitale, Vito; Heinrich, Victoria J.; Liggett, Daniela; Arndt, Stefanie; et al (October 2020, Bulletin of the American Meteorological Society)

   null (Ed.)

   Abstract The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a special observing period (SOP) that ran from 16 November 2018 to 15 February 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2,200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes yield the greatest forecast improvement for deep cyclones near the Antarctic coast. The SOP data have been applied to provide insights on an atmospheric river event during the YOPP-SH SOP that presented a challenging forecast and that impacted southern South America and the Antarctic Peninsula. YOPP-SH data have also been applied in determinations that seasonal predictions by coupled atmosphere–ocean–sea ice models struggle to capture the spatial and temporal characteristics of the Antarctic sea ice minimum. Education, outreach, and communication activities have supported the YOPP-SH SOP efforts. Based on the success of this Antarctic summer YOPP-SH SOP, a winter YOPP-SH SOP is being organized to support explorations of Antarctic atmospheric predictability in the austral cold season when the southern sea ice cover is rapidly expanding. 

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2. Winter Targeted Observing Periods during the Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

   https://doi.org/10.1175/BAMS-D-22-0249.1  

   Bromwich, David H; Gorodetskaya, Irina V; Carpentier, Scott; Alexander, Simon; Bazile, Eric; Heinrich, Victoria J; Massonnet, Francois; Powers, Jordan G; Carrasco, Jorge F; Cayette, Arthur; et al (September 2024, Bulletin of the American Meteorological Society)

   Abstract The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) held seven targeted observing periods (TOPs) during the 2022 austral winter to enhance atmospheric predictability over the Southern Ocean and Antarctica. The TOPs of 5–10-day duration each featured the release of additional radiosonde balloons, more than doubling the routine sounding program at the 24 participating stations run by 14 nations, together with process-oriented observations at selected sites. These extra sounding data are evaluated for their impact on forecast skill via data denial experiments with the goal of refining the observing system to improve numerical weather prediction for winter conditions. Extensive observations focusing on clouds and precipitation primarily during atmospheric river (AR) events are being applied to refine model microphysical parameterizations for the ubiquitous mixed-phase clouds that frequently impact coastal Antarctica. Process studies are being facilitated by high-time-resolution series of observations and forecast model output via the YOPP Model Intercomparison and Improvement Project (YOPPsiteMIIP). Parallel investigations are broadening the scope and impact of the YOPP-SH winter TOPs. Studies of the Antarctic tourist industry’s use of weather services show the scope for much greater awareness of the availability of forecast products and the skill they exhibit. The Sea Ice Prediction Network South (SIPN South) analysis of predictions of the sea ice growth period reveals that the forecast skill is superior to the sea ice retreat phase. 

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3. Effects of assimilation of YOPP‐SH additional radiosonde observations on analyses and forecasts over Antarctica in austral summer

   https://doi.org/10.1002/qj.4528  

   Choi, Yonghan; Kim, Seong‐Joong; Bromwich, David H.; Powers, Jordan G.; Kwon, Hataek; Park, Sang‐Jong (October 2023, Quarterly Journal of the Royal Meteorological Society)

   Radiosonde observations over Antarctica and the surrounding oceans were enhanced during the Year of Polar Prediction in the Southern Hemisphere (YOPP‐SH) summer Special Observing Period (SOP). Observing System Experiments (OSEs) were conducted in a continuous cycling framework using the Weather Research and Forecasting (WRF) Model and its data assimilation system. Routinely available observations were assimilated in the CTL (control) experiment, and special radiosonde observations from the YOPP‐SH SOP were additionally assimilated in the YOPP experiment. The results were compared to investigate the effects of additional radiosonde observations on analyses and forecasts over and around Antarctica. Verifications against ERA5 re‐analysis, radiosonde observations, and Automatic Weather Station (AWS) observations show overall positive effects of additional radiosonde observations. These positive effects are most noticeable in temperature at lower levels at earlier forecast lead times; afterward, wind forecast improvements at upper levels are the most noticeable. Although routine and special radiosonde observations are concentrated over the eastern and coastal regions of Antarctica (compared to the western and inland regions), the effects of the extra data spread in longitudinal and latitudinal directions; therefore, the effects on the forecasts are not limited to only the areas near the radiosonde observations. A case study reveals how cyclone forecasts are improved through the assimilation of the additional YOPP‐SH SOP radiosonde observations. This study provides insights into future observation strategies in Antarctica, such as horizontal/vertical observation locations, observation variables, and so forth to maximize effects of new observations on forecasts over Antarctica. 

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4. Transient Climate Sensitivity Shaped by Low Cloud Changes Remotely Driven by Southern Ocean Processes

   https://doi.org/10.1175/JCLI-D-24-0164.1  

   Ford, Robert_R; Rose, Brian_E_J; Rencurrel, M_Cameron (February 2025, Journal of Climate)

   Abstract Transient climate sensitivity is strongly shaped by geographical patterns of ocean heat uptake (OHU). To isolate the effects of uncertainties associated with OHU, a single slab ocean model is forced with doubled CO₂and an ensemble of OHU patterns diagnosed from transient warming scenarios in 12 fully coupled models. The single-model ensemble produces a wide range of Southern Ocean (SO) sea surface temperature (SST) and Antarctic sea ice responses, which are in turn associated with a 1.1–2.0-K range of transient climate response (TCR). Feedback analysis attributes the TCR spread primarily to shortwave effects of low clouds in the Southern Hemisphere (SH) midlatitudes. These cloud changes are strongly positively correlated with storm-track eddy kinetic energy. It is argued that midlatitude clouds (and thus planetary albedo) are remotely driven by SO SST and Antarctic sea ice, mediated by large-scale changes in SH baroclinicity and lower-tropospheric stability. The robustness of this atmospheric teleconnection between SO SST, Antarctic sea ice, and global feedback through midlatitude clouds is supported through additional simulations that explore more extreme SST and sea ice perturbations. These results highlight the importance of understanding physical relationships between SST, sea ice, circulation, and cloud changes in the SH as a pathway to better constraining transient climate sensitivity. Significance StatementAlthough it is well known that Earth’s global-mean surface temperature increases with increasing atmospheric CO₂, there are still significant uncertainties in the temperature and sea ice trends over the Southern Ocean region. Using a climate model, we find that Southern Ocean temperature and Antarctic sea ice changes can result in substantial cloud cover changes over the Southern Hemisphere, which play a primary role in determining the amount of warming in our experiments. We suggest that, in order to reduce uncertainty in future climate change, more work is needed to understand how the climate of the southern polar region can affect the circulation and clouds of the midlatitudes. 

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5. Expedition 382 Preliminary Report: Iceberg Alley and Subantarctic Ice and Ocean Dynamics

   https://doi.org/10.14379/iodp.pr.382.2019  

   Weber, M.E.; Raymo, M.E.; Peck, V.L.; Williams, T. (August 2019, Preliminary report)

   null (Ed.)

   International Ocean Discovery Program (IODP) Expedition 382, Iceberg Alley and Subantarctic Ice and Ocean Dynamics, investigated the long-term climate history of Antarctica, seeking to understand how polar ice sheets responded to changes in insolation and atmospheric CO2 in the past and how ice sheet evolution influenced global sea level and vice versa. Five sites (U1534–U1538) were drilled east of the Drake Passage: two sites at 53.2°S at the northern edge of the Scotia Sea and three sites at 57.4°–59.4°S in the southern Scotia Sea. We recovered continuously deposited late Neogene sediment to reconstruct the past history and variability in Antarctic Ice Sheet (AIS) mass loss and associated changes in oceanic and atmospheric circulation. The sites from the southern Scotia Sea (Sites U1536–U1538) will be used to study the Neogene flux of icebergs through “Iceberg Alley,” the main pathway along which icebergs calved from the margin of the AIS travel as they move equatorward into the warmer waters of the Antarctic Circumpolar Current (ACC). In particular, sediments from this area will allow us to assess the magnitude of iceberg flux during key times of AIS evolution, including the following: • The middle Miocene glacial intensification of the East Antarctic Ice Sheet, • The mid-Pliocene warm period, • The late Pliocene glacial expansion of the West Antarctic Ice Sheet, • The mid-Pleistocene transition (MPT), and • The “warm interglacials” and glacial terminations of the last 800 ky. We will use the geochemical provenance of iceberg-rafted detritus and other glacially eroded material to determine regional sources of AIS mass loss. We will also address interhemispheric phasing of ice sheet growth and decay, study the distribution and history of land-based versus marine-based ice sheets around the continent over time, and explore the links between AIS variability and global sea level. By comparing north–south variations across the Scotia Sea between the Pirie Basin (Site U1538) and the Dove Basin (Sites U1536 and U1537), Expedition 382 will also deliver critical information on how climate changes in the Southern Ocean affect ocean circulation through the Drake Passage, meridional overturning in the region, water mass production, ocean–atmosphere CO2 transfer by wind-induced upwelling, sea ice variability, bottom water outflow from the Weddell Sea, Antarctic weathering inputs, and changes in oceanic and atmospheric fronts in the vicinity of the ACC. Comparing changes in dust proxy records between the Scotia Sea and Antarctic ice cores will also provide a detailed reconstruction of changes in the Southern Hemisphere westerlies on millennial and orbital timescales for the last 800 ky. Extending the ocean dust record beyond the last 800 ky will help to evaluate dust-climate couplings since the Pliocene, the potential role of dust in iron fertilization and atmospheric CO2 drawdown during glacials, and whether dust input to Antarctica played a role in the MPT. The principal scientific objective of Subantarctic Front Sites U1534 and U1535 at the northern limit of the Scotia Sea is to reconstruct and understand how ocean circulation and intermediate water formation responds to changes in climate with a special focus on the connectivity between the Atlantic and Pacific basins, the “cold water route.” The Subantarctic Front contourite drift, deposited between 400 and 2000 m water depth on the northern flank of an east–west trending trough off the Chilean continental shelf, is ideally situated to monitor millennial- to orbital-scale variability in the export of Antarctic Intermediate Water beneath the Subantarctic Front. During Expedition 382, we recovered continuously deposited sediments from this drift spanning the late Pleistocene (from ~0.78 Ma to recent) and from the late Pliocene (~3.1–2.6 Ma). These sites are expected to yield a wide array of paleoceanographic records that can be used to interpret past changes in the density structure of the Atlantic sector of the Southern Ocean, track migrations of the Subantarctic Front, and give insights into the role and evolution of the cold water route over significant climate episodes, including the following: • The most recent warm interglacials of the late Pleistocene and • The intensification of Northern Hemisphere glaciation. 

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