The Pacific Warm Pool (PWP) is characterised by a mean sea surface temperature (SST) exceeding 28 deg C (the minimum surface water temperature that supports deep convection), weak trade winds, and the resultant deep convection, with thunderstorm tops exceeding 15 km.
This body of water, which spans the western waters of the equatorial Pacific, holds the warmest seawaters in the world. Because this area of warm water pushes west into the Indian Ocean, it is also often referred to as the Indo-Pacific Warm Pool.
Scientists found that, over a period of roughly two decades, the warm pool’s average annual temperatures and dimensions (the area enclosed within the 28 deg C isotherm) increase and then decrease like a slowly pulsating beacon.
Because these waters are hot enough to drive heat and moisture high into the atmosphere (by convection), the warm pool has a large effect on the climate of surrounding lands. It has been called the “heat engine of the world” and plays a key role in climate and monsoon variability for many nations throughout Asia and Africa and also influences remote regions and large scale climate models of variability. Furthermore, the size and intensity of the warm pool fluctuates with the El Niño–Southern Oscillation (ENSO). During El Nino events, the PWP expands horizontally but shrinks in vertical depth. The opposite occurs during La Nina.
Overall in recent years, the PWP has increased in both horizontal coverage and vertical depth. This is believed due to global warming.