Weather systems in the southern Indian Ocean (SIO) drive synoptic-scale precipitation variability in East Antarctica and southern Australia. Improved understanding of these dynamical linkages is beneficial to diagnose long-term climate changes from climate proxy records as well as informing regional weather and climate forecasts. Self-organising maps (SOMs) are used to group daily 500hPa geopotential height (z500; ERA-Interim) anomalies into nine regional synoptic types based on their dominant patterns over the SIO (30°-75°S, 40°-180°E) from January 1979-October 2018. The pattern anomalies represented include four meridional, three mixed meridional/zonal, one zonal and one transitional node. The frequency of the meridional nodes shows limited association with the phase of the Southern Annular Mode (SAM), especially during SON. The zonal and mixed patterns were nevertheless strongly and significantly correlated with SAM, although the regional synoptic representation of SAM+ conditions was not zonally symmetric and was represented by three separate nodes. We recommend consideration of how different synoptic conditions vary the atmospheric representation of SAM+ in any given season in the SIO. These different types of SAM+ mean a hemispheric index fails to capture the regional variability in surface weather conditions that is primarily driven by the synoptic variability rather than the absolute polarity of the SAM.

Although the Antarctic Ice Sheet (AIS) contribution to sea level rise is heavily influenced by ocean-driven mass loss (e.g., Edwards et al., 2019;Seroussi et al., 2020), the effects of sub-decadal to decadal precipitation variation on surface mass balance (SMB) dominate the overall mass balance variability of East Antarctica (IMBIE, 2018). A detailed understanding of SMB variability is therefore crucial to assess the future contribution of Antarctica to sea level rise (Seroussi et al., 2020). Uncertainties in future SMB changes contribute substantially to uncertainties in the projected Antarctic contribution to sea level rise, which varies between −7.8 and 43 cm sea level equivalent by 2100 under Representative Concentration Pathway (RCP) 8.5 scenario (Edwards et al., 2019(Edwards et al., , 2021Seroussi et al., 2020). Estimates of regional scale SMB distribution and trends remain difficult to obtain as high-resolution data remain very scarce (e.g., Favier et al., 2017;Lenaerts et al., 2019). The strong variability of Antarctic SMB, both in time and space, further complicates this effort. Precipitation over most regions of Antarctica is controlled by a few high precipitation events (Turner et al., 2019). This characteristic has to be understood and correctly represented in models for accurate projections.The strongly baroclinic Southern Ocean exhibits a high rate of cyclogenesis, and the southern Indian Ocean sector exhibits the highest frequency and strongest zone of cyclogenesis of the southern mid-latitudes (Simmonds et al., 2003). Yet, only a few of these cyclones actually reach the Antarctic coastline, and even fewer generate high precipitation events (

Abstract. Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially. Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k working group has compiled a database of two species, sodium [Na+] and sulphate [SO42-], commonly measured ionic species. The database contains records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against climate observations, to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.

Abstract. Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially, prior to the satellite era (1970 onwards). Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k (CLimate Variability in Antarctica and the Southern Hemisphere over the past 2000 years) working group has compiled a database of two species, sodium [Na+] and sulfate [SO42-], commonly measured ionic species. The database (https://doi.org/10.5285/9E0ED16E-F2AB-4372-8DF3-FDE7E388C9A7; Thomas et al., 2022) comprises records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against sea ice concentration, geopotential height (500 hPa), and surface wind fields to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.