Influence of Sea Ice Anomalies on Antarctic Precipitation and its Source Attribution

Thursday, December 15, 2016 - 13:40
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Modeling and experimental evidence suggests that Antarctic Ice Sheet (AIS) surface mass balance (SMB) increases in a warming climate due to increased precipitation, which has the potential to offset a significant portion of the overall AIS mass loss due to oceanic processes. However, the exact coupled-climate mechanisms behind this increase have not been well elucidated. In particular, the roles of sea surface temperature (SST) increases, sea ice loss, atmospheric moisture sources and transport, and atmospheric dynamical changes have not been clearly disaggregated. We use a variant of the Community Earth System Model (CESM) with explicit water tagging capability to partition the causes of increased precipitation in high latitudes. A set of sensitivity experiments has been conducted to understand the impact of sea ice anomalies on regional evaporation, moisture transport, and source-receptor relationships for precipitation over the Antarctic. Three composites of sea ice concentrations (SIC), which were constructed from the 1800-year fully-coupled control simulation of the CESM Large Ensemble Project (Kay et al., 2015) using mean, 10% lowest, and 10% highest SIC years (and corresponding SST), respectively, have been employed to drive 11-year atmosphere-only simulations under present-day radiative forcing conditions. Moisture sources in twenty-five geographical regions are explicitly tracked using the water tagging capability, which can help establish source-receptor relationships of vapor and precipitation in high latitudes. Results show that vapor sources for precipitation in high latitudes primarily originate from lower latitudes; however, the tagged vapor source regions in mid- and high latitudes have discernable changes in their contributions to precipitation over the Antarctic in response to the SIC changes. There is also a strong zonal and seasonal variability in vapor source attributions.

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