Continuous wintertime water vapor profiling by Raman lidar at Neumayer Station III, Antarctica: Characteristics of meridional moisture transport and assessment of ERA5 reanalysis

Abstract. The vertical distribution of water vapor is essential for understanding moisture transport toward Antarctica, which influences the surface mass balance of the ice sheets via precipitation, sublimation and longwave radiation effects. However, high-resolution vertical water vapor observations remain limited. In this study, we present continuous water vapor mixing ratio (WVMR) profiles obtained with Raman lidar at Neumayer Station III, Antarctica during wintertime (May to August) 2023. The observations reveal a mean WVMR of 0.7 gkg⁻¹ and capture an exceptional moist air intrusion in early July with WVMR values reaching up to 3.9 gkg⁻¹. Two dominant synoptic patterns driving moisture advection toward the Antarctic coast could be identified, producing distinctly different vertical moisture structures. Pattern A, with a low-pressure system northwest of Neumayer Station III seems to be more effective in transporting moisture than a low-pressure system northeast of the Station (pattern B). The lidar measurements are compared to ERA5 reanalysis humidity fields. While ERA5 generally reproduces the moisture distribution reasonably well, it exhibits a dry bias of 0.1 gkg⁻¹ (≈ 10 %) in the lower troposphere. Potential causes of the bias were investigated. The bias shows no clear dependence on the air mass source region, but is dependent on the assimilation cycle, synoptic conditions and the surface type representation in ERA5. These findings suggest that uncertainties in boundary layer mixing processes are a major contributor to the observed dry bias. The results highlight the value of continuous high-resolution water vapor profiling in understanding Antarctic moisture transport and validating reanalysis products.