Combined GNSS reflectometry–refractometry for automated and continuous in situ surface mass balance estimation on an Antarctic ice shelf

Reliable in situ surface mass balance (SMB) estimates in polar regions are scarce due to limited spatial and temporal data availability. This study aims at deriving automated and continuous specific SMB time series for fast-moving parts of ice sheets and shelves (flow velocity &gt; 10 m a−1) by developing a combined global navigation satellite system (GNSS) reflectometry and refractometry (GNSS-RR) method. In situ snow density, snow water equivalent (SWE), and snow deposition or erosion are estimated simultaneously as an average over an area of several square meters and independently on weather conditions. The combined GNSS-RR method is validated and investigated regarding its applicability to a moving, high-latitude ice shelf. A combined GNSS-RR system was therefore installed in November 2021 on the Ekström ice shelf (flow velocity ≈ 150 m a−1) in Dronning Maud Land, Antarctica. The reflected and refracted GNSS observations from the site are post-processed to obtain snow accumulation (deposition and erosion), SWE, and snow density estimates with a 15 min temporal resolution. The results of the first 16 months of data show a high level of agreement with manual and automated reference observations from the same site. Snow accumulation, SWE, and density are derived with uncertainties of around 9 cm, 40 kg m−2 a−1, and 72 kg m−3, respectively. This pilot study forms the basis for extending observational networks with GNSS-RR capabilities, particularly in polar regions. Regional climate models, local snow modeling, and extensive remote sensing data products will profit from calibration and validation based on such in situ time series, especially if many such sensors will be deployed over larger regional scales.</p

Seasonal and interannual variability of landfast sea ice in Atka Bay, Weddell Sea, Antarctica

Landfast sea ice (fast ice) attached to Antarctic (near-)coastal elements is a critical component of the local physical and ecological systems. Through its direct coupling with the atmosphere and ocean, fast-ice properties are also a potential indicator of processes related to a changing climate. However, in situ fast-ice observations in Antarctica are extremely sparse because of logistical challenges and harsh environmental conditions. Since 2010, a monitoring program observing the seasonal evolution of fast ice in Atka Bay has been conducted as part of the Antarctic Fast Ice Network (AFIN). The bay is located on the northeastern edge of Ekström Ice Shelf in the eastern Weddell Sea, close to the German wintering station Neumayer III. A number of sampling sites have been regularly revisited each year between annual ice formation and breakup to obtain a continuous record of sea-ice and sub-ice platelet-layer thickness, as well as snow depth and freeboard across the bay. Here, we present the time series of these measurements over the last 9 years. Combining them with observations from the nearby Neumayer III meteorological observatory as well as auxiliary satellite images enables us to relate the seasonal and interannual fast-ice cycle to the factors that influence their evolution. On average, the annual consolidated fast-ice thickness at the end of the growth season is about 2 m, with a loose platelet layer of 4 m thickness beneath and 0.70 m thick snow on top. Results highlight the predominately seasonal character of the fast-ice regime in Atka Bay without a significant interannual trend in any of the observed variables over the 9-year observation period. Also, no changes are evident when comparing with sporadic measurements in the 1980s and 1990s. It is shown that strong easterly winds in the area govern the year-round snow distribution and also trigger the breakup of fast ice in the bay during summer months. Due to the substantial snow accumulation on the fast ice, a characteristic feature is frequent negative freeboard, associated flooding of the snow–ice interface, and a likely subsequent snow ice formation. The buoyant platelet layer beneath negates the snow weight to some extent, but snow thermodynamics is identified as the main driver of the energy and mass budgets for the fast-ice cover in Atka Bay. The new knowledge of the seasonal and interannual variability of fast-ice properties from the present study helps to improve our understanding of interactions between atmosphere, fast ice, ocean, and ice shelves in one of the key regions of Antarctica and calls for intensified multidisciplinary studies in this region

German Contribution to YOPP-SH

Four projects with contributions from the German institutes Alfred-Wegener-Institut (AWI), the Leibniz Institute for Tropospheric Research (TROPOS) and the University of Trier support the YOPP mission by intensifying observations and advancing understanding of polar processes. During the Special Observing Period (SOP) for YOPP-SH AWI will increase radiosoundings at the Antarctic research station Neumayer and onboard the icebreaker Polarstern to four sondes per day (00, 06, 12, 18 UTC, project AWImet). AWI will also ensure continued operation of two automatic weather stations in Antarctica at least until the end of the SOP. Some 20 autonomous buoys measuring sea-ice parameters such as sea-ice and snow thickness as well as ice-drift velocity will be deployed in the eastern Wedell Sea around Feb./Mar. 2018 (project IPAB) by AWI. Additional buoys will be deployed on the fast-ice area in front of Neumayer Station in May/June 2018. Intentionally, these buoys will drift with the Weddell Gyre and still deliver data during the SOP. Buoys for ocean surface drift velocity could also be deployed on the Polarstern cruise in January 2019, but funding is still required. During the Antarctic season 2016/17 the Swiss-lead Antarctic Circumnavigation Expedition was conducted. As partner of the “Study of Preindustrial-like-Aerosol Climate Effects” (SPACE) project TROPOS carried out various aerosol measurements with special focus on particles able to act as cloud condensation nuclei and on particles able to nucleate ice. The overall aim of this project is to improve the understanding of aerosol-cloud interactions in the pristine Antarctic atmosphere. Quality assured measurement data shall be made available through GASSP and EBAS databases. During Polarstern cruise PS111 from Jan. till March 2018 wind lidar measurements will be carried out in the Weddell sea by the University of Trier. Measurements include horizontal and vertical scan programs to deduce wind profiles. Depending on weather conditions, data up to 1 km (and in single cases up to 2 km) can be collected, with a spatial resolution of 10m and temporal resolution of 15 min. The data, along with other Antarctic atmospheric measurements during YOPP, will be used in high-resolution atmospheric simulations (5km) for model verification and improvement of parameterizations

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

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a Special Observing Period (SOP) that ran from November 16, 2018 to February 15, 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2200 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

Continuous meteorological surface measurement during POLARSTERN cruise PS106/1 (ARK-XXXI/1.1)

The meteorological observatory Polarstern continuously acquires meteorological parameters during times of ship operation. Measurements are taken on various locations on the vessel, instrument heights above sea level are given below. All data is quality controlled. Measurements are checked daily on board by the operator and again prior to publication. Knowingly affected or erroneous data is removed