Seminars at the Faculty of Informatics

Regimes in the Southern Hemisphere Climate System

The Faculty of Informatics is pleased to announce a seminar given by Terence O'Kane

DATE: Thursday, September 26th, 2013
PLACE: USI Lugano Campus, room SI-008, Informatics building (Via G. Buffi 13)
TIME: 16.30

Using model process studies and non-stationary clustering techniques we examine changes in the metastability of the southern hemisphere climate system.

A purely data-driven approach for parametrisation is employed using a finite element bounded variation vector auto-regressive cluster methodology whereby a multi-scale approximation to non-stationary dynamical processes is achieved through optimal sequences of locally stationary fast Vector Auto-Regressive Factor (VARX) processes and some slow (or persistent) hidden process switching between them.

Our analysis of the mid-latitude atmosphere characterises quasi-stationary regimes in both reanalysed and model data sets prior to 1978 as positive and negative phases of a hemispheric mid-latitude blocking state with the Southern Annular Mode (SAM) associated with a transition state. Post 1978, SAM emerges as a true metastable state replacing the negative phase of the hemispheric blocking pattern. The hidden state frequency of occurrences exhibits strong trends. The blocking pattern dominates in the early 1980s then gradually decreases with a corresponding increase in the SAM frequency of occurrence. The major drivers of these changes are shown to be anthropogenic CO2 and stratospheric O3 depletion. Process studies using an atmospheric GCM show substantial changes to the Hadley cell and sub-tropical jet can occur through CO2 changes independent of O3 depletion.

An Ocean General Circulation Model (OGCM) forced by the observed atmospheric fields analysed above is then used to identify intrinsic modes of low frequency variability in the Southern Ocean. A comprehensive suite of experiments elucidates excitation and amplification responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. Non-stationary cluster analysis reveals fundamental changes to the meta-stability of the Southern Ocean dynamics in response to changes in atmospheric forcing.

Dr O'Kane received his MSc in theoretical physics in 1999 (University of Melbourne) and PhD in applied mathematics in 2003 (Monash University). Between 2003 and 2007 he held postdoctoral and research fellow positions at CSIRO Atmospheric Research and the Antarctic Climate and Ecosystems CRC. From 2007-2009 he was ensemble prediction scientist at the Australian Bureau of Meteorology where he developed the Australian Global & Regional Ensemble Prediction System for operational weather forecasting. Since 2009 he has worked on atmospheric and ocean dynamics and predictability at CSIRO Marine Research in Hobart.
In 2013 for his outstanding original contributions to difficult and important problems in applied mathematics he was awarded the prestigeous JH Michell Medal from ANZIAM and the Australian Mathematical Society.

HOST: Prof. Illia Horenko