Links between Large-Scale Modes of Climate Variability and Synoptic Weather Patterns in the Southern Indian Ocean

Abstract

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.

Australian rainfall variability—Why is the eastern seaboard of Australia different to the rest of Australia and also internally inhomogeneous

“…Further, such insights are a necessary first step in understanding how rainfall patterns could change in the future. Records such as the extended ECL record of Browning and Goodwin (Browning Stuart A. Goodwin Ian D., 2016), cyclone classification approaches (e.g., Catto, 2016; Cavicchia et al ., 2019), and insights from palaeoclimate reconstructions (e.g., Udy et al ., 2021) should be utilized to achieve this. When re‐evaluating the influence of ECLs over a longer record, analysis should also include the use of gridded rainfall data as opposed to the ARDD to enable insights at a higher resolution as well as assessment of the sensitivity of excluding rainfall in the lead‐up to an ECL developing in the Tasman Sea.…”

El Niño–Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

“…Previous studies have reported snow accumulation of 0.680 m yr −1 IE (Roberts et al, 2015; and low mean wind speeds of 8.3 m s −1 (Morgan et al, 1997). The new LD ice core used in this study, DSS1617, was drilled in summer 2016/2017 and is intended to replace and extend the upper portion of the LD record presented in Vance et al (2013), which used four successive short ice cores to cover the period 1990-2009. The new record presented here will extend to 2016, increasing overlap with the satellite era (and therefore calibration period) by 7 years (or 19 %) and reducing dating errors associated with combining multiple short ice core composites.…”

“…The new record presented here will extend to 2016, increasing overlap with the satellite era (and therefore calibration period) by 7 years (or 19 %) and reducing dating errors associated with combining multiple short ice core composites. Prior to 1990, the LD ice core record used in this study is the same as that used in Vance et al (2013), DSS97. The DSS1617 and DSS97 ice core composites were combined using visual analysis of raw data of overlapping seasonal cycles in 1989/1990 using key dating analytes (see Sect.…”

“…Chloride was used as a proxy for sea salt in this study to maintain comparability with Vance et al (2013), although sodium was also considered. We acknowledge that Na + is the more conservative proxy for sea salt (particularly in the Northern Hemisphere); however, we wished to compare like for like with LD in Vance et al (2013).…”

“…Donat-Magnin et al, 2020). The ENSO also influences East Antarctica; for example, there is an ENSO signal preserved in the summer sea salt record from LD (Vance et al, 2013).…”