Marilyn Raphael - Modeling the annual cycle of daily Antarctic sea ice extent

Event type: 
28 February 2020
2.00pm - 3.00pm

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Dr. Marilyn Raphael
The University of California, Los Angeles.
Climate Change Research Centre

The total Antarctic sea ice extent (SIE) experiences a distinct annual cycle, peaking in September and troughing in March. In this presentation, we decompose the annual cycle into a set of components each one of which is interpretable and, when combined, they give a complete picture of the variation of the sea ice. Time scales varying from the instantaneous, and not previously defined, to the multidecadal curvilinear trend, the longest are presented. Because the representation is daily, these timescales of variability give precise information about the timing and rates of advance and retreat of the ice and may be used to diagnose physical contributors to variability in the sea ice. A number of annual cycles are defined, each capturing different components of variation, especially the yearly amplitude and phase that are major contributors to SIE variation. Using daily sea ice concentration data, we show that our proposed invariant annual cycle explains 29% more of the variation of daily SIE than the traditional method. The proposed annual cycle that incorporates amplitude and phase variation explains 77% more variation than the traditional method. The variation in phase explains more of the variability in SIE than the amplitude. We show that the long term trend in daily Antarctic sea ice extent is strongly curvilinear and the reported positive linear trend is small and dependent strongly on a positive trend that began around 2011 and continued until 2016.The methodology is used to analyse the anomalous decay of sea ice in 2016, showing that it was associated largely with a change of phase rather than amplitude. The methodology is also used to compare the SIE simulated by a CMIP6 climate system model with observed SIE.

Brief Biography: Marilyn Raphael is a professor of Geography at the University of California, Los Angeles. She is Chair of the SCAR expert group Antarctic Sea ice Processes and Climate (ASPeCt) and co-Lead of the WCRP’s Polar Climate Predictability Initiative (PCPI). Her research interests are in climate variability and change particularly in the high latitude Southern Hemisphere. Her research focuses on the interaction between Antarctic sea-ice variability and the large-scale atmospheric circulation using both largescale observational databases and global climate models. Her current projects focus on understanding the contemporary variability in Antarctic sea ice, quantifying the links between the sea ice variability and atmospheric circulation features such as the semi-annual oscillation (SAO) and zonal wave three (ZW3) and reconstructing Antarctic sea ice extent and concentration for the 20th century.