How long is the memory of tropical ocean dynamics?

Combining classic equatorial wave dynamics and midlatitude wave dynamics, a unified view is proposed to account for the memory of tropical ocean dynamics in terms of oceanic basin modes. It is shown that the dynamic memory of the ocean is bounded by the cross-basin time of planetary waves along the poleward basin boundary. For realistic ocean basins, this memory originates from the mid- and high-latitude processes and is usually at interdecadal timescales.