Trajectory patterns of the annual cycle of the heat centre of the Indo-Pacific warm pool

The modulated annual cycle (MAC) of the Indo-Pacific warm pool (IPWP) heat centre location is investigated using the empirical mode decomposition-ensemble empirical mode decomposition method. The MAC and its interannual variability mainly affect the zonal and vertical locations of the heat centre; in fall and winter of El Nino years, the heat centre moves eastward from its normal location, with very little change in its meridional position. Four patterns of the heat centre trajectory in the IPWP are identified using the self-organizing map algorithm. Patterns 1 and 3 are both similar to a saddle, but pattern 1 is more winding. The shapes of patterns 2 and 4 are similar, but tilt in different directions: pattern 2 tilts southwest whereas pattern 4 tilts west. Of all the four patterns, the persistence of pattern 2 is generally relatively high. The trajectory of the heat centre develops in the sequence of patterns: 1-2-4-3-1. Pattern 1 (pattern 4) is related to the cold (warm) phase of the El Nino-Southern Oscillation (ENSO), while pattern 2 (pattern 3) corresponds to the negative (positive) phase of Indian Ocean dipole (IOD). The sequence of patterns in the trajectory of the heat centre in the IPWP is related to the IOD-ENSO interactions on a biennial timescale.