报告人：Carsten S. Frederiksen
单 位：Centre for Australian Weather and Climate Research, Bureau of Meteorology, Australia.
时 间：2014年5月16日，上午10:00
地 点：40号楼319会议室
A new methodology is proposed that allows patterns of interannual covariability, or teleconnections, between the intraseasonal and slow components of seasonal mean Australian rainfall and the corresponding components in the Southern Hemisphere atmospheric circulation to be estimated. In all seasons, the dominant rainfall — circulation teleconnections in the intraseasonal component are shown to have the characteristic features associated with well-known intraseasonal dynamical and statistical atmospheric modes and their relationship with rainfall. Thus, for example, there are patterns of interannual covariability that reflect rainfall relationships with the intraseasonal Southern Annular Mode, the Madden-Julian Oscillation and wavenumber 3 and 4 intraseasonal modes of variability.
The predictive characteristics of the atmospheric circulation - rainfall relationship are shown to reside with the slow components. In all seasons, we find rainfall-circulation teleconnections in the slow components related to the El Ni？o-Southern Oscillation. Each season also has a coupled mode, with a statistically significant trend in the time series of the atmospheric component that appears to be related to recent observed trends in rainfall. The slow Southern Annular Mode also features in association with southern Australian rainfall, especially during austral winter and spring. There is also evidence of an influence of Indian Ocean sea surface temperature variability on rainfall in southeast Australia during austral winter and spring.
An assessment of the CMIP5 models in reproducing these coupled patterns will also be presented. An ensemble of “good” models is used to isolate an externally forced coupled “trend” mode which is related to changes in radiative forcing. This is shown to be consistent with observed changes in Australian rainfall and in winter to be associated with changes in the storm tracks.