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

Abstract. We present three 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, δ_T) 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, 50 (37–73) sr for NAT, and 52 (40–65) sr for ice PSC. For cirrus, the median LR is 49 (34–52) sr. These values are consistent with microphysical expectations and with previous groundbased and spaceborne lidar studies.

The Young–optimized subset yields 41 (31–61) sr for STS, 61 (38–78) sr for NAT, 38 (32–38) sr for the few remaining ice PSC, and 41 (31–41) sr for cirrus although for this latter case the number of observations is not statistically significant. The subset thus provides a conservative estimate of the accuracy of the results from the full dataset which can capture the full range of cloud variability.

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.