Evaluating the Twentieth Century Reanalysis Version 3 with synoptic typing and East Antarctic ice core accumulation

Abstract. Weather systems in the southern Indian Ocean influence East Antarctic precipitation variability and surface mass balance. However, long term variability in synoptic-scale weather systems in this region is not well understood due to short instrumental records that are mostly limited to the satellite era (post 1979). Ice core records from coastal East Antarctica suggest significant decadal variability in snowfall accumulation, indicating that data from the satellite era alone is not enough to characterise climate variability in the high southern latitudes. It is therefore challenging to contextualise recent precipitation trends and extremes in relation to climate change in this area. We used synoptic typing of daily 500 hPa geopotential height anomalies and the Law Dome ice core (East Antarctica) annual snowfall accumulation record to investigate whether the Twentieth Century Reanalysis project can represent the synoptic conditions associated with increased precipitation at Law Dome prior to the satellite era. Twelve synoptic types were identified using self-organising maps based on their dominant pressure anomaly patterns over the southern Indian Ocean, with four types associated with above average daily precipitation at Law Dome. Our results indicate that the Twentieth Century Reanalysis project can reliably represent the meridional synoptic conditions associated with increased precipitation at Law Dome from 1948, aligning with the assimilation of consistent surface pressure data from weather stations in the southern Indian Ocean. This extends the time period available to contextualise recent trends and extremes in precipitation and synoptic weather conditions by up to three decades beyond the satellite era. These results will help contextualise East Antarctic surface mass balance variability prior to the satellite era, with implications for improved understanding of the largest source of potential sea level rise.