Baroclinic Rossby Waves With Phase Lag Cause Seasonal Upward‐Propagating Signals in the Mid‐Depth Equatorial Pacific Ocean

AbstractBased on OFES outputs verified by mooring observations, the seasonal characteristics in the middepth (1,000–3,000 m) equatorial Pacific Ocean are investigated in detail. The seasonal upward‐propagating signals, consisting of one positive and one negative anomaly, are identified at the equator. The harmonic analyses indicate that the seasonal variations in the middepth equatorial Pacific Ocean originate from the downward‐propagating energy dominated by the first meridional modes of Rossby waves. The superposition of first and second baroclinic modes of Rossby waves could reproduce the seasonal variations. Furthermore, a series of superposition experiments show that the phase lag between the two modes needs to be in the range of 0 to π to cause upward phase propagation. It implies that the baroclinic modes in the seasonal variations may not be generated simultaneously so that the Rossby waves with specific phase lag can cause upward‐propagating signals in the middepth equatorial Pacific Ocean. This new finding will enhance the understanding of seasonal variations in the middepth equatorial Pacific Ocean.