Atmospheric Water Vapor Monitoring on Horseshoe Island, Antarctica: GNSS Observations at the Permanent TUR1 and TUR2 Stations Using a Regional Tm Calibration

Atmospheric water vapor plays a critical role in the climate system, governing energy balance, climate variability and precipitation processes. Accurate monitoring of precipitable water vapor (PWV) is therefore essential for both meteorological and climate-related studies. The Global Navigation Satellite System (GNSS) provides an effective and continuous tool for PWV estimation through the calculation of zenith tropospheric wet delay (ZWD). Given the scarcity of continuous ground-based observations in Antarctica, the TUR1 and TUR2 permanent GNSS stations, established on Horseshoe Island during the Turkish Antarctic Expedition-4 (TAE-4) under the TÜBİTAK Polar Research Project (No. 118Y322), provide a valuable infrastructure for continuous atmospheric water vapor monitoring, which constitutes the primary contribution of this study. The conversion of ZWD to PWV requires an accurate estimation of the weighted mean temperature (Tm), which is typically derived from empirical models. However, globally applied Tm models may not adequately represent the regional atmospheric variability of high-latitude environments, where the vertical atmospheric structure and water vapor distribution differ substantially from mid-latitude conditions. This limitation is especially pronounced in Antarctica, which serves as a natural laboratory for climate change research while remaining one of the most observationally constrained regions on Earth due to sparse meteorological infrastructure and logistical challenges. In this study, a locally derived Tm parameterization (HRS) was obtained from radiosonde profiles at near sea-level stations within the 66°S–70°S latitude belt and evaluated against both the existing regional Antarctic Tm model (ANT) and the globally applied GPT2, GPT3 and Bevis models, using radiosonde observations as an independent reference. The HRS parameterization reproduced the radiosonde-derived Tm values with an RMSE of 2.90 K, clearly outperforming the global models (4.20–4.51 K) and showing close agreement with the existing regional Antarctic Tm model (r = 0.987), independently confirming the transferability of the regional approach to the Horseshoe Island region. The GNSS-derived PWV based on the regional Tm parameterization was then evaluated against ERA5 reanalysis data as an independent reference. The estimates showed strong agreement, with a correlation of 0.95, an RMSE of 1.65 mm and a mean bias of +1.22 mm, the seasonal agreement being strongest in austral summer (RMSE ≈ 1.24 mm) and weakest in austral winter (RMSE ≈ 1.92 mm), consistent with the lower water vapor content and stronger surface temperature inversions that characterize the cold season. The close agreement between the two independent TUR1 and TUR2 stations further supports the repeatability of GNSS-based PWV retrieval under coastal Antarctic conditions, highlighting the observational value of these stations for atmospheric water vapor monitoring in Antarctica, where continuous observations remain limited.