<scp>ERA5</scp> deficit in supercooled liquid water cloud radiative forcing at Dome C, Antarctica

Abstract Clouds play a crucial role in estimating Earth's climate evolution, with their impact depending on their composition whether they contain solid or liquid water. In Antarctica, clouds containing supercooled liquid water (SLW), which exists at temperatures below 0°C, are challenging to observe and often poorly represented in climate models. A recent observational study conducted at Dome C, Concordia station (75°06′ S, 123°21′ E, 3233 m altitude) on the Eastern Antarctic Plateau revealed a logarithmic relationship between liquid water path (LWP, liquid water profile integrated along the vertical) and SLW cloud radiative forcing (CRF) during summer (December 2018–2021). To assess whether this relationship holds over a longer period, we analysed meteorological reanalyses from ERA5 for December from 1940 to the present. Our analysis indicates that, during December 2018–2021, the ERA5 distribution of SLW CRF–LWP conforms to the observational relationship and remains within its domain of validity. ERA5 SLW CRF varies from 0 to a maximum of 55 W·m −2 when LWP varies from 0.1 to a maximum of 1.4 g·m −2 . But the maximum of SLW CRF in ERA5 underestimates the observations by approximately −15 W·m −2 (∼20%) attributed to biases in long‐wave downward SLW CRF (accounting for two‐thirds of the deficit) and short‐wave SLW CRF (one‐third). Our study reveals a notable increase in summertime SLW clouds from the 1980s to the contemporary era with no significant change prior to the 1980s when the reanalysis data quality in the 1940s degrades. The increase of SLW clouds may be explained by the positive trend in maximum in‐cloud temperatures (from −23°C in the 1940s to −18°C in the 2020s). Our findings emphasise the need for improved representation of SLW clouds in numerical weather prediction and climate models to enhance projections of climate evolution.