Evaporative controls on Antarctic precipitation: An ECHAM6 model study using novel water tracer diagnostics

• Main Authors: Gao, Qinggang, Sime, Louise C., McLaren, Alison, Bracegirdle, Thomas J., Capron, Emilie, Rhodes, Rachael H., Steen-Larsen, Hans Christian, Shi, Xiaoxu, Werner, Martin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Antarctic; Southern Ocean; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/egusphere-2023-1041; https://noa.gwlb.de/receive/cop_mods_00066991; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00065461/egusphere-2023-1041.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1041/egusphere-2023-1041.pdf

Improving our understanding of the controls on Antarctic precipitation is critical for gaining insights into polar, and global changes. Here we develop and implement innovative water tracing diagnostics in the atmospheric general circulation model ECHAM6. These tracers provide new precise information on moisture source locations and properties of Antarctic precipitation. In our preindustrial simulation, annual mean Antarctic precipitation originating from the open ocean has a source latitude range of 49–35° S; a source sea surface temperature range of 9.8–16.3 °C; a source 2 m relative humidity range of 75.6–83.3 %; and a source 10 m wind speed (wind10) range of 10.1 to 11.3 m s-1. The tendency of poleward vapour transport to follow moist isentropes means that central Antarctic precipitation is sourced from more equatorward (distant) sources via elevated transport pathways than coastal Antarctic precipitation. We find however this tendency breaks down in the lower troposphere, likely due to diabatic cooling. Heavy precipitation is sourced by longer-range moisture transport: it comes from 2.9° (300 km, averaged over Antarctica) more equatorward (distant) sources compared to the rest of precipitation. Precipitation during negative phases of the Southern Annular Mode (SAM) also comes from more equatorward moisture sources (by 2.4°, averaged over Antarctica) than precipitation during positive SAM phases, likely due to amplified planetary waves during negative SAM phases. Moreover, source wind10 of annual mean precipitation is on average 2.1 m s-1 higher than annual mean wind10 at the evaporation source locations from which the precipitation originates. This shows that the evaporation of moisture driving Antarctic precipitation occurs under windier conditions than average. This is the first time this particular thermodynamic control of Southern Ocean surface wind on moisture availability for Antarctic precipitation has been quantified. Overall, our novel water tracing diagnostics enhance our understanding of the ...