3.6.7 Other Indices

As noted earlier, many patterns of variability (sometimes referred to as ‘modes’) in the climate system have been identified over the years, but few stand out as robust and dynamically significant features in relation to understanding regional climate change. This section discusses two climate signals that have recently drawn the attention of scientific community: the Antarctic Circumpolar Wave and the Indian Ocean Dipole.

3.6.7.1 Antarctic Circumpolar Wave

The Antarctic Circumpolar Wave (ACW) is described as a pattern of variability with an approximately four-year period in the southern high-latitude ocean-atmosphere system, characterised by the eastward propagation of anomalies in antarctic sea ice extent, and coupled to anomalies in SST, sea surface height, MSLP and wind (Jacobs and Mitchell, 1996; White and Peterson, 1996; White and Annis, 2004). Since its initial formulation (White and Peterson, 1996), questions have arisen concerning many aspects of the ACW: the robustness of the ACW on inter-decadal time scales (Carril and Navarra, 2001; Connolley, 2003; Simmonds, 2003), its generating mechanisms (Cai and Baines, 2001; Venegas, 2003; White et al., 2004; White and Simmonds, 2006) and even its very existence (Park et al., 2004).