Experimental determination of the lidar ratio for cirrus and polar stratospheric clouds at Dome C, Antarctica, using a Young inversion

Abstract

Abstract. We present 3 years (2022–2024) of polarisation lidar observations of polar stratospheric clouds (PSCs) and tropospheric cirrus above Concordia Station (Dome C, Antarctica). Layer-mean lidar ratios (LR) at 532 nm are retrieved using the Young inversion method applied to an elastic backscatter and depolarisation (Rayleigh) lidar. The measurements are classified in the (1-1/R,δT) phase space, allowing us to separate supercooled ternary solution (STS), nitric-acid trihydrate (NAT) and ice PSC, as well as upper-tropospheric cirrus. To quantify the impact of the Young assumptions, we analyse both the full set of cloud detections and a Young-optimized subset of clouds that satisfy stricter homogeneity conditions above and below the cloud layer. The comparison between these two datasets allows us to separate the effective climatological variability of lidar ratio values from those retrieved under idealised conditions that strictly satisfy the Young inversion assumptions. For PSCs, the full dataset yields optically weighted median LR values (25–75 percentiles) of 38 (31–52) sr for STS, 49 (37–67) sr for NAT, and 52 (41–66) sr for ice PSC. For cirrus, the median LR is 50 (33–52) sr. These values are consistent with microphysical expectations and with previous ground-based and spaceborne lidar studies. The Young-optimized subset yields 38 (31–59) sr for STS, 59 (38–74) sr for NAT, 38 (32–38) sr for the few remaining ice PSC, and 40 (32–40) sr for cirrus although for this latter case the number of observations is not statistically significant. The subset thus provides a conservative methodological benchmark for conditions that most closely satisfy the Young inversion assumptions, while the full dataset captures the broader range of cloud variability. The comparison between the full dataset and the Young-optimized subset shows that the retrieved LR statistics are not controlled only by particle type, but also by cloud structural complexity and mixing. In particular, ice PSC and some cirrus layers frequently violate the vertical homogeneity assumptions of the Young method, so that their layer-mean LR should be interpreted as an effective value representative of mixed or vertically structured clouds rather than as a pure microphysical signature. These values provide a physically consistent reference for PSC and cirrus retrievals over Dome C and can be used in radiative-transfer modelling and satellite-lidar validation.