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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-organizing maps (SOMs) are used to group daily 500-hPa 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 to 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 September-November. 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. [ABSTRACT FROM AUTHOR]

The first atmospheric observations of octafluorooxolane (octafluorotetrahydrofuran, c - C4F8O), a persistent greenhouse gas, are reported. In addition, a complementary laboratory study of its most likely atmospheric loss processes, its infrared absorption spectrum, and global warming potential (GWP) are reported. First atmospheric measurements of c - C4F8O are provided from the Cape Grim Air Archive (41 ∘ S, Tasmania, Australia, 1978–present), supplemented by two firn air samples from Antarctica, in situ measurements of ambient air at Aspendale, Victoria (38 ∘ S), and a few archived air samples from the Northern Hemisphere. The atmospheric abundance in the Southern Hemisphere has monotonically grown over the past decades and leveled at 74 ppq (parts per quadrillion, femtomole per mole in dry air) by 2015–2018. The growth rate of c - C4F8O has decreased from a maximum in 2004 of 4.0 to <0.25 ppq yr -1 in 2017 and 2018. Using a 12-box atmospheric transport model, globally averaged yearly emissions and abundances of c - C4F8O are calculated for 1951–2018. Emissions, which we speculate to derive predominantly from usage of c - C4F8O as a solvent in the semiconductor industry, peaked at 0.15 (±0.04 , 2 σ) kt yr -1 in 2004 and have since declined to <0.015 kt yr -1 in 2017 and 2018. Cumulative emissions over the full range of our record amount to 2.8 (2.4–3.3) kt, which correspond to 34 Mt of CO2 -equivalent emissions. Infrared and ultraviolet absorption spectra for c - C4F8O as well as the reactive channel rate coefficient for the O(1D) + c - C4F8O reaction were determined from laboratory studies. On the basis of these experiments, a radiative efficiency of 0.430 W m -2 ppb -1 (parts per billion, nanomol mol -1) was determined, which is one of the largest found for synthetic greenhouse gases. The global annually averaged atmospheric lifetime, including mesospheric loss, is estimated to be >3 000 years. GWPs of 8975, 12 000, and 16 000 are estimated for the 20-, 100-, and 500-year time horizons, respectively. [ABSTRACT FROM AUTHOR]