GFI/BCCR Seminar: Cold air outbreaks in the South Pacific: climatology, dynamics and impacts on air-sea heat fluxes

Lukas Papritz (ETH, Zurich, Sveits):

Cold air outbreaks in the South Pacific: climatology, dynamics and impacts on air-sea heat fluxes

Abstract
A climatology of cold air outbreaks (CAOs) in the high-latitudes of the South Pacific based on the ERA-Interim dataset is presented. Two major and distinct regions with frequent CAOs from autumn to spring are identified, one in the Ross Sea and another in the Amundsen and Bellingshausen Seas. Based on kinematic backward trajectories it is quantified that more than 40% of the air masses leading to a CAO originate from the Antarctic continent and descend substantially, with the Ross Ice Shelf corridor as the major pathway. CAO trajectories descending from the Antarctic continent differ from those originating over sea ice by a much lower specific humidity, stronger diabatic cooling and much more intense adiabatic warming.

In winter CAOs are the major contributor to the net turbulent heat flux from the ocean over much of the high-latitudes and we show that variations in the frequency of CAOs are largely responsible for the interannual variability of the winter turbulent heat flux. Finally, we study the linkage of CAOs to the extratropical stormtrack and show that in the Amundsen and Bellingshausen Seas precipitation associated with the passage of extratropical cyclones near the sea ice boundary is compensated by intense evaporation in CAOs induced by the cyclone circulation