Arnold Sullivan, Wenju Cai and Tim Cowan 4th February 2010, AMOS Is Climate Change Contributing the Skewness Towards more Frequent Consecutive Positive Indian Ocean Dipole Events? Arnold Sullivan, Wenju Cai and Tim Cowan 4th February 2010, AMOS

Indian Ocean Dipoles Climate change? Cai, et al. 2009a The Dipole Mode Index is defined as the SST anomaly difference between the eastern (eastern Africa coast) and the western tropical Indian Ocean (western Sumatra coast). The IOD in its positive (or "anomalous") mode is characterized by cooling of surface waters in the southeastern equatorial Indian Ocean and warming in the western equatorial Indian Ocean. The changes in SST during IOD events are found to be associated with changes in the surface wind field of the central equatorial Indian Ocean. In fact, the winds reverse from the usual westerly to an easterly direction during positive IOD events (Saji et al., 1999; Behera and Yamagata, 2001). Furthermore, the atmospheric convection that is normally situated over the eastern Indian Ocean warm pool shifts to the west. This configuration results in heavy rain in eastern Africa and leaves the Indonesian region with little rain, resulting in droughts and forest fires. Fundamental questions about IOD’s independence from the ENSO, its natural modes of variability and its interaction with the Asian monsoon have been raised. Cai, et al. 2009a Climate change? CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

The IOD patterns in IPCC-AR4 models: 1950-1999 Raw SON anomaly SST & apply EOF on IO domain and detrend. We use regression spatial map to show how climate models reproduce IOD. If the patterns do not show what we expect then that model has to be eliminated. We focus on austral spring, because the IOD is matured. We show 24 models compare with observed and sort by the IOD amplitude. There are five models did not pass our exam, 19 left. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

IOD Circulation Trend Trends in ensemble-average suggests an increase in pIOD due to the response of climate change on the IO. Cai, W., A. Sullivan, and T. Cowan (2009), Climate change contributes to more frequent consecutive positive Indian Ocean Dipole events, Geophys. Res. Lett., 36, L23704 Multi-model averaging largely cancels the variability-driven component. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Number of pIOD Then we calculate number of pIOD in this two data sets. Increase the number of consecutive pIOD events. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Impacts on IOD Properties Easterlies off the Sumatra-Java coast and along the equatorial IO. Well-built SST gradients across the east and west IO. Strengthened upwelling and a shallowing thermocline. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Forcing of the IO Mean Circulation Changes What drives the pIOD-like mean circulation changes? El Niño-Southern Oscillation Southern Annular Mode Asian Monsoon For any of these drivers to be the forcing, they must satisfy: The greater variability of the driver, the stronger correlation between that driver and the IOD. We use detrended data to test. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

ENSO & IOD (SON) The statistical relationship showing that models with greater variability of the driver produce a stronger correlation between that driver and the IOD. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

ENSO induced Trend Pattern This ENSO induced trend pattern suggests that if a trend toward a high El Nino phase is produced, it could contribute to a pIOD-like mean circulation trend. The trend also display easterlies over the equatorial eastern IO, conductive to a change toward a pIOD-like state, and westerly over the western Pacific indicative of a weaker Walker circulation as produced by most models. However ENSO induced trend in the east IO are smaller than the total IOD trend pattern, which means ENSO is not the only forcing. Consistent thermocline shallowing in the eastern IO and western Pacific. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

But ENSO’s influence is not enough CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

SAM & IOD (SON) SAM is not driving IOD. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Land Sea heating contrast In the mean circulation trends, the Asian monsoon is strengthening. Does models support this mechanism? Monsoon variability? Spatial correlation maps indicate that the direct IOD- monsoon interaction involves IOD-like temperature and wind anomalies in the eastern IOD region. Abram, N. J., M. K. Gagan, J. E. Cole, W. S. Hantoro, and M. Mudelsee (2008), Recent intensification of tropical climate variability in the Indian Ocean, Nat. Geosci., 1(12), 849– 853. Bakun, A. (1990), Global climate change and intensification of coastal ocean upwelling. Science 247, 198–201. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Land Sea heating contrast cont’ The climate changes are likely to be accompanied by increases in the frequency and severity of IOD events, and possibly a strengthening interdependence between IOD and Asian monsoon variability. Most models showing a faster warming rate over land than over the ocean (red area). CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

The pIOD increases by about 17%. Conclusions In a warming climate, a pIOD-like mean circulation trend is consistent with an increase in the number of pIOD events. The pIOD increases by about 17%. The circulation trends are in turn consistent with wind changes associated with a weaker Walker circulation in the Pacific and an enhanced land-sea temperature contrast in the Indian Ocean sector. Climate change provides a favourable environment for pIOD development. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Thank you Contact Us Phone: 1300 363 400 or +61 3 9239 4525 Email: arnold.sullivan@csiro.au Web: www.csiro.au Thank you CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

The Indian Ocean Dipoles. Introduction The Indian Ocean Dipoles. How do the 20th century IPCC-AR4 models present the IOD? What drives the pIOD-like mean Circulation changes? ENSO Southern Annular Mode Monsoon variability CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Inter-model variations again show the 5 bad models Between global ENSO SST pattern & global IOD SST pattern Coherence between IODE index and Nino34. The rarity is not due to an overly strong model ENSO-IOD coherence. Cai, et al. 2008 CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

ENSO & IOD (SON) The statistical relationship showing that models with greater variability of the driver produce a stronger correlation between that driver and the IOD. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010

Supplementary Information for Abram, N. J. , Gagan, M. K. , Cole, J. E Supplementary Information for Abram, N.J., Gagan, M.K., Cole, J.E., Hantoro, W.S. and Mudelsee, M. (2008) Recent intensification of tropical climate variability in the Indian Ocean. Nature Geoscience. CSIRO. Arnold Sullivan, Climate Change & IOD, CMAR 4 February 2010