A033-0005
Southern Ocean latitudinal gradients of Cloud Condensation Nuclei

Tuesday, 8 December 2020
Poster
Ruhi Humphries1, Sean Gribben2, Ian McRobert3, Jason Ward1, Melita D Keywood1, Paul W Selleck1, Connor J. Flynn4, James Harnwell1, Gerald G Mace5, Alain Protat6 and Simon Alexander7, (1)Climate Science Centre, CSIRO Oceans & Atmosphere, Aspendale, Australia, (2)Climate Science Centre, CSIRO Oceans & Atmosphere, Aspendale, VIC, Australia, (3)CSIRO Oceans & Atmosphere, Hobart, Australia, (4)University of Oklahoma, School of Meteorology, Norman, OK, United States, (5)Univ Utah, Salt Lake City, UT, United States, (6)Bureau of Meteorology, Melbourne, Australia, (7)Australian Antarctic Division, Kingston, TAS, Australia
Abstract:
The Southern Ocean has been plagued by a dearth of measurements for decades, owing to its harsh environment far from major population centres. Since 2015, there has been a flurry of measurements, most notably continuous measurements aboard the RV Investigator which houses the world’s first mobile station of the Global Atmosphere Watch, as well as numerous significant campaigns in the region. In this study, we utilise aerosol and cloud condensation nuclei (CCN) measurements made aboard the Aurora Australis during the MARCUS campaign in the 2017/18 austral summer, together with concurrent measurements made aboard the RV Investigator during the CAPRICORN-II voyage, part of the larger SOCRATES campaign.

Aerosol data (CN10 and CCN at numerous supersaturations) free from platform exhaust, were divided into 5o latitudinal bins. The northern-most bin (40-45oS) was found, unsurprisingly, to exhibit the highest concentrations (CCN0.2 ~100 cm-3; CCN0.5 ~250 cm-3; CN10 ~600 cm-3), with back-trajectory analyses revealing substantial influence from continental sources of Tasmania and to a lesser extent, Victoria. Latitudinal bins between 45-65oS were reasonably consistent (CCN0.2 ~ 100 cm-3; CCN0.5 150 cm-3; CN10 ~300 cm-3), with trajectories showing a marine boundary layer source region from the south-west. CCN measurements in this latitudinal range agreed with concurrent measurements at Macquarie Island and at Cape Grim. The southern-most latitudinal bin (65-70oS) showed a distinct change in populations, with increases in aerosol concentrations (CCN0.2 ~130 cm-3; CCN0.5 250 cm-3; CN10 ~350 cm-3) and CCN/CN10 ratios, consistent with previous measurements resulting from transitioning across the atmospheric polar front. Analyses to further understand these changes showed corresponding increases in sulfate aerosols, decreases in sea-salt aerosol and decreases in both wind speed and precipitation influence.

This dataset is important observational data that will help verify climate and earth system models, and constrain satellite data. These data also help to untangle the mystery of the compositional changes consistently observed across the atmospheric polar front.

<< Previous Abstract | Next Abstract >>