A new Asymmetric Mode of internal variability for the Global Ocean

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• Nathan Bindoff (University of Tasmania)
• Monday 03 July 2023, 15:00-16:00
• BAS Seminar Room 1; https://ukri.zoom.us/j/92110296123.

If you have a question about this talk, please contact Dr Michael Haigh.

Global ocean heat distribution is driven by both internal and external factors. Among internal factors, the climate modes such as Indian Ocean Dipole (IOD), subsurface Dipole Mode (SDM) of the Indian Ocean, El Nino Southern Oscillation (ENSO), Interdecadal Pacific Oscillation (IPO) over the Pacific, North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO) over the Atlantic etc. have a substantial impact on global ocean heat transport between the hemispheres. However, the combination of existing climate modes is not enough to explain the total variability in the global ocean internal to the system. By analysing 30 CMIP5 pre-Industrial control simulations our study suggests that global ocean shows an internal climate mode named as Asymmetric mode (ASYM) that drives the heat transport (and mass) between the hemispheres. The ASYM is characterised as the changes in the sea level and ocean heat content of the global ocean with sea level high (low) and warming (cooling) in the southern (northern) hemisphere and vice-versa. ASYM is unique as it is defined over the global ocean and expressed in terms of sea level and ocean heat content, in contrast to other climate modes which are largely defined based on sea surface temperature and regional ocean.

Our preliminary analysis suggests that the periodicity of ASYM varies from interannual to decadal to multidecadal timescales. Climate parameters such as surface air temperature, surface winds, precipitation, sea surface salinity and sea level pressure are observed to be closely associated with ASYM . The footprint in Antarctica and Southern Ocean is large and offers the potential explanation for the observed acceleration of the ACC (and other impacts) and rapid warming of the Southern Ocean (in excess of human driven climate change).

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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