Synoptic conditions and atmospheric moisture pathways associated with virga and precipitation over coastal Adélie Land in Antarctica

Abstract

Abstract. Precipitation falling over the coastal regions of Antarctica often experiences low-level sublimation within the dry katabatic layer. The amount of water that reaches the ground surface is thereby considerably reduced. This paper investigates the synoptic conditions and the atmospheric transport pathways of moisture that lead to either virga – when precipitation is completely sublimated – or actual surface precipitation events over coastal Adélie Land, East Antarctica. For this purpose, the study combines ground-based lidar and radar measurements at Dumont d'Urville station (DDU), Lagrangian back trajectories, Eulerian diagnostics of extratropical cyclones and fronts, and moisture source estimations. It is found that precipitating systems at DDU are associated with warm fronts of cyclones that are located to the west of Adélie Land. Virga – corresponding to 36 % of the hours with precipitation above DDU – and surface precipitation cases are associated with the same precipitating system but they correspond to different phases of the event. Virga cases more often precede surface precipitation. They sometimes follow surface precipitation in the warm sector of the cyclone's frontal system, when the associated cyclone has moved to the east of Adélie Land and the precipitation intensity has weakened. On their way to DDU, the air parcels that ultimately precipitate above the station experience a large-scale lifting across the warm front. The lifting generally occurs earlier in time and farther from the station for virga than for precipitation. It is further shown that the water contained in the snow falling above DDU during pre-precipitation virga has an oceanic origin farther away (about 30∘ more to the west) from Adélie Land than the one contained in the snow that precipitates down to the ground surface.

Mixed‐Phase Clouds and Precipitation in Southern Ocean Cyclones and Cloud Systems Observed Poleward of 64°S by Ship‐Based Cloud Radar and Lidar

“…For the two Mawson case studies, the cyclones decayed as they propagated eastward. All events showed the typical three stages of cloud and precipitation observed in cloud systems along the East Antarctic coastline, specifically, (i) preprecipitation virga falling out of SLW layers at the start of the event, (ii) precipitation reaching the surface (characterized by the strong radar reflectivities) during the event, and finally (iii) postprecipitation virga in the trailing SLW layers (Jullien et al., 2020), Multiple layers of SLW cloud were embedded within ice clouds of large vertical extent (i.e., several kilometers deep) for several hours during the central phase of each event (see Figures 3, 9, and 14). This consistent cloud and virga/precipitation structure observed during all three events suggests the ubiquitous occurrence of SLW layers within synoptic‐scale cloud systems in the high‐latitude austral summer Southern Ocean.…”

Present and Future of Rainfall in Antarctica

“…Our knowledge gap regarding Antarctic rain primarily lies in the technical difficulties in measuring precipitation in the harsh meteorological conditions prevailing on the remote Antarctic continent. Insights might be gained from remotely sensed measurements at stations where radars have been deployed (e.g., Gorodetskaya et al., 2015; Grazioli et al., 2017; Jullien et al., 2020). Preliminary analyses of radar vertical profiles at DDU suggest that during rain events, the melting layer is found in the first hundreds of meters above the ground (Vignon, Besic, et al., 2019).…”

Biogeochemistry and Physics of the Southern Ocean-Atmosphere System Explored With Data Science

“…This confirms the back trajectory analysis (see supplementary information section S4) showing that the maritime air advection happens in the upper marine boundary layer, while near-surface layers are dominated by a concurrent advection of continental air. The latter vertical atmospheric structure has been observed at the Adélie Coast during the advection of moist air at upper levels in the warm sector of extratropical cyclones (Vignon et al, 2019;Jullien et al, 2020).…”