Tropical western Pacific warm pool and maritime continent precipitation rates and their contrasting relationships with the Walker Circulation

The Cenozoic reorganization of islands in the Maritime Continent region of the tropical western Pacific may have increased the amount of land surface area, changed the distribution of sea surface temperature (SST), and consequently provided a necessary condition for the onset of the Walker Circulation. Precipitation rates over the Maritime Continent, measured with the Tropical Rainfall Measurement Mission (TRMM) satellite and generated from the Climate Prediction Center Merged Analysis of Precipitation (CMAP), correlate positively with a variety of measures of the Walker Circulation's strength (surface easterlies and high‐level westerlies over the western Pacific) and hence with La Niña conditions. Similarly measured precipitation rates over the western Pacific warm pool correlate positively with the strength of tropical zonal circulation shifted to the east, and thus a weakened Walker Circulation and stronger El Niño‐like conditions. Areas of high precipitation rates correlate with areas of ascent in the atmosphere and with high SST. Condensation associated with precipitation over the warm pool provides about twice the amount of latent heating as that over the Maritime Continent largely because the surface area of the warm pool is about 1.9 times larger than that of the Maritime Continent. These results support the conjecture that tectonic expansion and reorganization of the Maritime Continent may have led to a strengthening of the Walker Circulation, and may be related to a change in tropical Pacific climate from a permanent and zonally uniform (El Niño‐like) state in Pre‐Ice Age time to the present day El Niño‐Southern Oscillation (ENSO) state.