final_program_abstracts[1]

11 IMSC Session Program
Using CMIP3 multi-models simulations to understand the
relationship between large-scale climate drivers
Monday - Parallel Session 5
Wenju Cai and Tim Cowan
CSIRO Marine and Atmospheric Research, Aspendale, Australia
Using models from the Third Coupled Model Inter-comparison Project (CMIP3)
simulations of individual global climate drivers have been examined, however the
relationship among them has not been fully assessed in a model framework. This is
carried out to address several important issues, including the possibility of the
Southern Annular Mode (SAM) forcing Indian Ocean Dipole (IOD) events, and the
likely impact of the IOD on El Niño-Southern Oscillation (ENSO) events and/or viceversa.
Several conclusions emerge from statistics based on multi-model outputs. Firstly,
ENSO signals project strongly onto the SAM, although ENSO-forced signals tend to
peak before ENSO. This feature is similar to the situation in the Indian Ocean, where
the IOD-induced signal over southern Australia peaks before the IOD itself, through
the emergence of steady equivalent barotropic wavetrains. Secondly, there is no
control by the SAM on the IOD, in contrast to what has been suggested previously.
Indeed, none of the CMIP3 models produces a SAM-IOD relationship that supports a
positive SAM driving a positive IOD event (Cai et al. 2010a). Thirdly, the IOD does
impact on ENSO, however in the majority of models this coherence is quite weak,
lower than has been observed (Cai et al. 2009). However, the ENSO’s influence is
boosted by a spurious oceanic teleconnection, whereby ENSO discharge/recharge
signals transmit to the Sumatra-Java coast, generating thermocline anomalies resulting
in changes in IOD properties. Without this spurious oceanic teleconnection, the
influence of the IOD on ENSO is comparable to the impact of ENSO on the IOD.
Also discussed is the well-known ENSO cold tongue, which leads to a complete
‘‘nonresponse to ENSO’’ in terms of rainfall along the central and eastern equatorial
Pacific in the majority of CMIP3 models. Climatological SSTs, which are far too cold
along the Pacific equator and extend too far west, have linkages to a weakness in the
teleconnection with Hawaii boreal winter rainfall and an inducement of an unrealistic
teleconnection with rainfall over west Papua New Guinea and northwest Australia in
austral summer (Cai et al. 2009, Cai et al. 2010b). Similar IOD-rainfall
teleconnections will also be discussed.
Cai, W., A. Sullivan, and T. Cowan (2009), Rainfall Teleconnections with Indo-
Pacific Variability in the WCRP CMIP3 Models. J. Climate, 22, 5046–5071.
Cai, W., A. Sullivan, and T. Cowan (2010a), Interactions of ENSO, the IOD, and the
SAM in CMIP3 models. J. Climate (submitted).
Cai, W., T. Cowan, J. Ribbe, G. Shi, and A. Sullivan (2010b), Summer rainfall over
Northwest Australia: will the observed increase continue? Geophys. Res. Lett. (under
review).
Abstracts 81