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

Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate long-term (multi-centennial) climate variability. Until recently, the Law Dome (Dome Summit South) ice core record remained one of few long-term high-resolution records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snowfall accumulation rates and sea salt concentrations in the upper portion (~21 m) of the Mount Brown South record, and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South record preserves a stronger signal for the El Niño-Southern Oscillation (ENSO; in austral winter and spring, r = 0.521, p r = −0.387, p = 0.018, Niño 3.4). The Mount Brown South and Law Dome ice cores record inverse signals for the ENSO, suggesting the occurrence of distinct moisture and aerosol intrusions. We suggest that ENSO-related sea surface temperature anomalies in the equatorial Pacific drive atmospheric teleconnections in the southern mid-latitudes. These anomalies are associated with a weakening (strengthening) of regional westerly winds to the north of Mount Brown South that corresponds to years of low (high) sea salt deposition at Mount Brown South during La Niña (El Niño) events. The Mount Brown South annual sea salt record when complete will offer a new proxy record for reconstructions of the ENSO over the recent millennium, along with improved understanding of regional atmospheric variability in the southern Indian Ocean in addition to that derived from Law Dome

Measurement report: Understanding the seasonal cycle of Southern Ocean aerosols

Published: 29 March 2023The remoteness and extreme conditions of the Southern Ocean and Antarctic region have meant that observations in this region are rare, and typically restricted to summertime during research or resupply voyages. Observations of aerosols outside of the summer season are typically limited to long-term stations, such as Kennaook / Cape Grim (KCG; 40.7∘ S, 144.7∘ E), which is situated in the northern latitudes of the Southern Ocean, and Antarctic research stations, such as the Japanese operated Syowa (SYO; 69.0∘ S, 39.6∘ E). Measurements in the midlatitudes of the Southern Ocean are important, particularly in light of recent observations that highlighted the latitudinal gradient that exists across the region in summertime. Here we present 2 years (March 2016–March 2018) of observations from Macquarie Island (MQI; 54.5∘ S, 159.0∘ E) of aerosol (condensation nuclei larger than 10 nm, CN10) and cloud condensation nuclei (CCN at various supersaturations) concentrations. This important multi-year data set is characterised, and its features are compared with the long-term data sets from KCG and SYO together with those from recent, regionally relevant voyages. CN10 concentrations were the highest at KCG by a factor of ∼50 % across all non-winter seasons compared to the other two stations, which were similar (summer medians of 530, 426 and 468 cm−3 at KCG, MQI and SYO, respectively). In wintertime, seasonal minima at KCG and MQI were similar (142 and 152 cm−3, respectively), with SYO being distinctly lower (87 cm−3), likely the result of the reduction in sea spray aerosol generation due to the sea ice ocean cover around the site. CN10 seasonal maxima were observed at the stations at different times of year, with KCG and MQI exhibiting January maxima and SYO having a distinct February high. Comparison of CCN0.5 data between KCG and MQI showed similar overall trends with summertime maxima and wintertime minima; however, KCG exhibited slightly (∼10 %) higher concentrations in summer (medians of 158 and 145 cm−3, respectively), whereas KCG showed ∼40 % lower concentrations than MQI in winter (medians of 57 and 92 cm−3, respectively). Spatial and temporal trends in the data were analysed further by contrasting data to coincident observations that occurred aboard several voyages of the RSV Aurora Australis and the RV Investigator. Results from this study are important for validating and improving our models and highlight the heterogeneity of this pristine region and the need for further long-term observations that capture the seasonal cycles.Ruhi S. Humphries, Melita D. Keywood, Jason P. Ward, James Harnwell, Simon P. Alexander, Andrew R. Klekociuk, Keiichiro Hara, Ian M. McRobert, Alain Protat, Joel Alroe, Luke T. Cravigan, Branka Miljevic, Zoran D. Ristovski, Robyn Schofield, Stephen R. Wilson, Connor J. Flynn, Gourihar R. Kulkarni, Gerald G. Mace, Greg M. McFarquhar, Scott D. Chambers, Alastair G. Williams, and Alan D. Griffith

Gravity wave and orographic wave activity observed around the Antarctic and Arctic stratospheric vortices by the COSMIC GPS-RO satellite constellation

[1] Polar stratospheric gravity wave activity is studied using data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System Radio Occultation (GPS-RO). Waves with vertical wavelengths of ∼2 to 15 km are considered. The temperature variance σ2 is used as a measure of wave activity and is studied on isentropic surfaces. Large intermittent orographic wave activity is identified during austral spring 2007 above the Patagonian Andes and the Antarctic Peninsula, where σ2 in the stratosphere increases by up to a factor of 5 for periods of 5 days to a few weeks. The σ2 are also investigated in equivalent latitudes to allow a direct comparison with the changing vortex structure. The October 2007 σ2 inside the Antarctic vortex boundary region at 400–600 K is one and a half times that outside the vortex. This region of enhanced σ2 descends in time and is not observed during the decay of the Arctic vortex. During the boreal winter of 2006/2007, orographic wave activity is observed above Scandinavia and Greenland. An analysis of the 400 K and the 450 K levels in both hemispheres shows a strong relationship between enhanced σ2 and the location of the vortex edge, suggesting that the waves observed are propagating poleward and are guided to higher altitudes by the vortex. The line of sight of the occultations shows a preference for north-south alignment, indicating that COSMIC favors the detection of orographic waves above the north-south oriented mountain ranges considered here.S. P. Alexander, A. R. Klekociuk, and T. Tsud

Future changes in stratospheric quasi-stationary wave-1 in the extratropical southern hemisphere spring and summer as simulated by ACCESS-CCM

Seasonally dependent quasi-stationary planetary wave activity in the southern hemisphere influences the distribution of ozone within and near the equatorward edge of the stratospheric polar vortex. Accurate representation of this zonal asymmetry in ozone is important in the characterisation of stratospheric circulation and climate and their associated effects at the surface. In this study, we used the Australian Community and Climate Earth System Simulator-Chemistry Climate Model to investigate the influence of greenhouse gases (GHGs) and ozone depleting substances (ODSs) on the zonal asymmetry of total column ozone (TCO) and 10 hPa zonal wind between 50 and 70°S. Sensitivity simulations were used from 1960 to 2100 with fixed ODSs and GHGs at 1960 levels and a regression model that uses equivalent effective stratospheric chlorine and carbon dioxide equivalent radiative forcing as the regressors. The model simulates the spring and summer zonal wave-1 reasonably well, albeit with a slight bias in the phase and amplitude compared to observations. An eastward shift in the TCO and 10 hPa zonal wave-1 is associated with both decreasing ozone and increasing GHGs. Amplitude increases are associated with ozone decline and amplitude decreases with GHG increases. The influence of ODSs typically outweigh those by GHGs, partly due to the GHG influence on TCO phase at 50°S likely being hampered by the Andes. Therefore, over the 21st century, influence from ozone recovery causes a westward shift and a decrease in amplitude. An exception is at 70°S during spring, where the GHG influence is larger than that of ozone recovery, causing a continued eastward trend throughout the 21st century. Also, GHGs have the largest influence on the 10 hPa zonal wave-1 phase, but still only induce a small change in the wave-1 amplitude. Different local longitudes also experience different rates of ozone recovery due to the changes in phase of the zonal wave-1. The results from this study have important implications for understanding future ozone layer distribution in the Southern Hemisphere under changing GHG and ODS concentrations. Important future work would involve conducting a similar study using a large ensemble of models to gain more statistically significant results.Kane A. Stone, Andrew R. Klekociuk and Robyn Schofiel

Low latitude 2-day planetary wave impact on austral polar mesopause temperatures: revealed by a January diminution in PMSE above Davis, Antarctica

[1] A new characteristic of the austral summer polar mesopause as revealed by ground-based radar and satellite temperature measurements is reported, that is linked to inter-annual variability of the low-latitude easterly wind jet. Four consecutive seasons of polar mesosphere summer echoes (PMSE) and mesosphere temperature observations above Davis, Antarctica (68.6°S) show a mid-January diminution in PMSE occurrence rate that coincides with a minor mesopause warming of several degrees. Spectral analyses of PMSE, Aura Microwave Limb Sounder (MLS) temperatures and radar meridional winds show the presence of ∼4–5-day planetary waves (PWs) throughout the austral summer in the polar upper mesosphere together with enhanced ∼2-day PW activity from mid-January to mid-February. Analysis of MLS temperatures show that the ∼2-day PWs have zonal wavenumbers (S) with both westward (S = −2, −3) and eastward (S = +2, +3) components. Although displaying some inter-annual variation in the peak onset time, the mid-January mesopause warming coincides with a weakening of the equatorward meridional wind above Davis and enhancement of low-latitude 2-day PW activity.Ray J. Morris, Andrew R. Klekociuk, and David A. Holdswort

A comparison of hydroxyl rotational temperatures from Davis (69degreesS, 78degreesE) with sodium lidar temperatures from Syowa (69degreesS, 39degreesE)

[1] We report the first substantive inter‐site comparison of high southern latitude mesopause region winter temperatures. Davis (69°S, 78°E) hydroxyl rotational nightly‐mean temperatures are significantly correlated with Syowa (69°S, 39°E) sodium lidar nightly‐mean temperatures at 87 km made in 2000 (correlation coefficient of 0.68) and 2001 (0.51) despite a site separation of ∼1500 km. The Davis winter average temperature in 2001, 203 K, differs from the Syowa value of 201 K only by the uncertainty in the measurement. A more substantial 7 K separates the year 2000 winter averages, Davis again being warmer. The temperature difference between the sites is attributed to either variations in the hydroxyl layer or short‐term cooling events in the mesopause region above Syowa that are not detected above Davis. Syowa winter temperatures at 87 km are ∼7 K cooler than for an equivalent latitude northern hemisphere site.G. B. Burns, T. D. Kawahara, W. J. R. French, A. Nomura, and A. R. Klekociu

Inter-hemispheric asymmetry in polar mesosphere summer echoes and temperature at 69 degrees latitude

Abstract not availableRay J.Morris, Andrew R.Klekociuk, Ralph Latteck, Werner Singer, David A. Holdsworth, Damian J. Murph

The 2019/2020 summer of Antarctic heatwaves

Version of Record online: 30 March 2020This summer, a heatwave across Antarctica saw temperatures soar above average. Temperatures above zero are especially significant because they accelerate ice melt. Casey Station had its highest temperature ever, reaching a maximum of 9.2°C and minimum of 2.5°C. The highest temperature in Antarctica was 20.75°C on 9 February. Here we discuss the biological implications of such extreme events.Sharon A. Robinson, Andrew R. Klekociuk, Diana H. King, Marisol Pizarro Rojas, Gustavo E. Zúñiga, Dana M. Bergstro

The 2007 Antarctic ozone hole

The 2007 Antarctic ozone hole is reviewed from a variety of perspectives, making use of various Australian data and analyses. The 2007 ozone hole was relatively modest, particularly in comparison to that of 2006, due in part to a disturbance to the polar vortex in early September that led to an influx of ozone-rich air. Ozone depiction was still severe however in the lower stratosphere. The long-term outlook for recovery is described, with Antarctic ozone currently forecast to return to 1980 levels around the period 2055-2080