predictability arises from ENSO and the global trend rather than extra-tropical processes and is thus limited to ~4 seasons. The prediction is consistent with the seasonal footprinting mechanism in which an optimal SST structure evolves into the ENSO mature phase 6–10 months later that subsequently impacts the North Pacific Ocean SST via the atmospheric bridge. Skills in predicting decadal PDO variability could arise from taking into account the impact of the externally forced and internally generated Pacific variability. Related patterns The interdecadal Pacific oscillation (IPO) is a similar but less localised phenomenon; it covers the Southern hemisphere as well (50°S to 50°N). ENSO tends to lead PDO cycling. Shifts in the IPO change the location and strength of ENSO activity. The South Pacific convergence zone moves northeast during El Niño and southwest during La Niña events. The same movement takes place during positive IPO and negative IPO phases respectively. (Folland et al., 2002) Interdecadal temperature variations in China are closely related to those of the NAO and the NPO. The amplitudes of the NAO and NPO increased in the 1960s and interannual variation patterns changed from 3–4 years to 8–15 years. Sea level rise is affected when large areas of water warm and expand, or cool and contract. See also California Current Hadley cell Ocean heat content Pacific–North American teleconnection pattern North Atlantic oscillation Atlantic multidecadal oscillation (AMO) References Further reading External links Regional climate effects Physical oceanography Pacific Ocean Climate oscillations